Studies into the Total Syntheses of Various Natural ... · various natural products and their derivatives for biological evaluation. ... using the Negishi and Suzuki cross-coupling

Studies into the Total Syntheses of Various

Natural Products and their Derivatives for

Biological Evaluation

Louisa Achini Ho

B. Sc. (Hons)

School of Chemistry and Biochemistry

This thesis is presented for the degree of Doctor of Philosophy to the University of

Western Australia, 2013.

Candidate Declaration

The work described in this thesis was carried out by the author in the School of

Chemistry and Biochemistry at the University of Western Australia under the

supervision of Associate Professor Scott G. Stewart, Professor Emilio Ghisalberti, and

Professor George C. T. Yeoh. This work has not been previously submitted for a degree

or diploma at any institution. To the best of my knowledge the work described herein is

original, and has not been previously published or written by another person except

where duly referenced.

Louisa A. Ho

2013

DECLARATION FOR THESES CONTAINING PUBLISHED WORK AND/OR

WORK PREPARED FOR PUBLICATION

The examination of the thesis is an examination of the work of the student. The work

must have been substantially conducted by the student during enrolment in the degree.

Where the thesis includes work to which others have contributed, the thesis must

include a statement that makes the student’s contribution clear to the examiners. This

may be in the form of a description of the precise contribution of the student to the work

presented for examination and/or a statement of the percentage of the work that was

done by the student.

In addition, in the case of co-authored publications included in the thesis, each author

must give their signed permission for the work to be included. If signatures from all the

authors cannot be obtained, the statement detailing the student’s contribution to the

work must be signed by the coordinating supervisor.

Please sign one of the statements below.

1. This thesis does not contain work that I have published, nor work under review for

publication.

2. This thesis contains only sole-authored work, some of which has been published

and/or prepared for publication under sole authorship. The bibliographical details of the

work and where it appears in the thesis are outlined below.

3. This thesis contains published work and/or work prepared for publication, some of

which has been co-authored. The bibliographical details of the work and where it

appears in the thesis are outlined below. The student must attach to this declaration a

statement for each publication that clarifies the contribution of the student to the work.

This may be in the form of a description of the precise contributions of the student to

the published work and/or a statement of percent contribution by the student. This

statement must be signed by all authors. If signatures from all the authors cannot be

obtained, the statement detailing the student’s contribution to the published work

must be signed by the coordinating supervisor.

1. Stewart, S. G.; Ho, L. A.; Polomska, M. E.; Percival, A. T.; Yeoh, G. C. T., Rapid Evaluation of

Antrodia camphorata Natural Products and Derivatives in Tumourigenic Liver Progenitor Cells

with a Novel Cell Proliferation Assay, ChemMedChem 2009, 4, 1657. Louisa Ho was

responsible for the experimental work described in this paper. Additionally, she wrote the

experimental section.

2. Xie, H.-d.; Ho, L.; Truelove, M.; Corry, B.; Stewart, S., Fluorescent Triphenyl Substituted

Maleimide Derivatives: Synthesis, Spectroscopy and Quantum Chemical Calculations Journal of

Fluorescence 2010, 20, 1077. Louisa Ho was responsible for the synthetic chemistry

experimental work described in this paper.

Student Signature:

Coordinating Supervisor Signature:

i

Abstract

This thesis describes three projects, all of which are linked by the central theme of

palladium-catalysed cross-coupling reactions as key steps in the total syntheses of

various natural products and their derivatives for biological evaluation.

Chapter 1 provides a brief introduction about natural products as synthetic targets, and

the role palladium-catalysed cross-coupling reactions have played in natural product

synthesis.

Chapter 2 details the total syntheses of Antrodia camphorata natural product maleimide

and maleic anhydrides (I, II, and III),1,2

in addition to a number of their aryl-

differentiated derivatives (e.g. IV and V) using the Negishi and Suzuki cross-coupling

reaction protocols as key synthetic steps. The chapter then discusses the ability of these

compounds to affect proliferation in non-tumourigenic and tumourigenic liver

progenitor cell lines as monitored by the Cellscreen system, a non-destructive rapid-

screening instrument.3 Several derivatives were found to radically slow the proliferation

of liver progenitor cells. However, of particular interest were two maleic anhydride

derivatives IV and V. These analogues demonstrated selectivity for limiting the

proliferation of tumourigenic progenitor cells in comparison with their non-

tumourigenic counterparts.

Chapter 3 describes a formal synthesis for the cyclohexenone epoxide natural product

SDEF 678,4 along with several approaches to the enantioselective total syntheses of

SDEF 678 and speciosins A-F.5 The formal synthesis for the natural product SDEF 678

is based around the use of a Sonogashira cross-coupling, a phenolic oxidation, a Diels–

Alder/retro-Diels–Alder sequence, and a diastereoselective epoxidation as key reaction

steps. The enantioselective approach to SDEF 678 describes a sequence involving a

ii

phenolic oxidation, a Sharpless epoxidation, a Corey-Fuchs reaction, a Sonogashira

cross-coupling, and a diastereoselective DIBALH-H reduction as key reaction steps.

In Chapter 4, several approaches towards the total syntheses of two new

pyrrolosesquiterpenes named glaciapyrrole B and glaciapyrrole C are described.6 The

synthetic approaches feature various intermolecular palladium-catalysed cross-coupling

processes (e.g. the Heck, Suzuki, and Sonogashira reactions, the last one indirectly) to

establish the central C-(sp2)-C(sp

2) bond between C8 and C9.

iii

Table of Contents

Abstract .............................................................................................................................. i

Acknowledgments ........................................................................................................... vii

List of Abbreviations........................................................................................................ ix

Chapter 1 General Introduction ......................................................................................... 1

1.1 Natural products as synthetic targets .................................................................. 3

1.2 Palladium-catalysed reactions in natural product synthesis ............................... 7

1.2.1 Palladium-catalysed cross-coupling reactions ............................................ 7

1.2.2 Palladium(0)-catalysts and electrophilic coupling partners ........................ 8

1.2.3 The general mechanism for the Negishi, Suzuki, and Sonogashira cross-

coupling reactions ..................................................................................................... 9

1.2.4 The Negishi reaction ................................................................................. 11

1.2.5 The Suzuki reaction................................................................................... 13

1.2.6 The Sonogashira reaction .......................................................................... 15

1.2.7 The Heck cross-coupling reaction ............................................................. 17

Chapter 2 The Total Syntheses of Antrodia camphorata Natural Products and their

Derivatives for Biological Evaluation ............................................................................. 21

2.1 Introduction ...................................................................................................... 23

2.1.1 Natural compounds as a source of pharmaceutical agents ........................ 23

2.1.2 Natural products and potential anticancer agents from Antrodia

camphorata ............................................................................................................. 24

2.1.3 Biological studies of Antrodia camphorata natural products 31-35 and

their derivatives as potential therapeutic agents for liver cancer ............................ 26

2.1.4 An introduction to the chemistry of maleimides and maleic anhydrides .. 27

2.1.5 Proposed synthesis .................................................................................... 28

2.1.6 Aims of research ....................................................................................... 32

2.2 The Syntheses of Antrodia camphorata maleic anhydride and maleimide

natural products and their derivatives ......................................................................... 33

2.2.1 The synthesis of dichloromaleimide 46 .................................................... 33

iv

2.2.2 The synthesis of isobutyl maleimide 48 .................................................... 34

2.2.3 The syntheses of boronic acid and ester Suzuki cross-coupling partners . 35

2.2.4 The syntheses of maleimide derivatives via the Suzuki reaction .............. 40

2.2.5 The syntheses of maleic anhydride derivatives......................................... 44

2.2.6 The syntheses of maleimide derivatives ................................................... 46

2.3 The Biological evaluation of Antrodia camphorata maleic anhydride and

maleimide natural products and their derivatives ....................................................... 51

2.3.1 Biological assay results for natural products 31-35 against PIL2 and PIL4

cell lines .................................................................................................................. 52

2.3.2 Biological assay results for maleic anhydride derivatives 97-105 against

PIL2 and PIL4 cell lines.......................................................................................... 54

2.3.3 Biological assay results for maleimides 109-116 against PIL2 and PIL4

cell lines ................................................................................................................. 57

2.3.4 Overview of biological assay results ........................................................ 60

2.4 Syntheses, spectroscopy, and quantum chemical calculations of fluorescent

maleimide derivatives ................................................................................................. 61

2.5 Conclusions and future work ............................................................................ 63

Chapter 3 Studies into the Total and Formal Syntheses of SDEF 678 and Speciosins

A-F .................................................................................................................................. 65

3.1 Introduction ...................................................................................................... 67

3.1.1 Cyclohexenone epoxide natural products ................................................. 67

3.1.2 Cyclohexenone epoxide natural products SDEF 678 (138) and speciosins

A-F (139-144) ......................................................................................................... 68

3.1.3 Masked para-benzoquinone ketals as key intermediates in the total

synthesis of cyclohexenone epoxides ..................................................................... 70

3.1.4 Phenolic oxidations using PIDA as a way to access masked benzoquinone

ketals ................................................................................................................... 71

3.1.5 Aims of research ....................................................................................... 74

3.1.6 Planned synthetic routes to SDEF 678 (138) and speciosins A-F (139-144)

................................................................................................................... 74

v

3.2 Efforts towards the total synthesis of SDEF 678 (138) and speciosins A-F

(138-144) ..................................................................................................................... 77

3.2.1 The synthesis of ketal 172 - pathway 1 ..................................................... 78

3.2.2 The synthesis of ketal 172 - pathway 2 ..................................................... 81

3.2.3 The attempted synthesis of ketal 172 - pathway 3 .................................... 85

3.2.4 The synthesis of epoxide 176 .................................................................... 86

3.2.5 The attempted synthesis of ketal alcohol 200 ........................................... 92

3.2.6 The attempted synthesis of bisketal 224 ................................................... 98

3.2.7 The attempted synthesis of ketal alcohol 239 ......................................... 101

3.2.8 The synthesis of aldehyde 177 ................................................................ 103

3.2.9 The synthesis of terminal alkyne 179 ..................................................... 104

3.2.10 The attempted synthesis of SDEF 678 (138) via tertiary alcohol 280 .... 116

3.2.11 The attempted synthesis of SDEF 678 (138) via alcohol 199 ................. 117

3.2.12 The synthesis of SDEF 678 (138) from terminal alkyne 179 ................. 123

3.3 The formal synthesis of SDEF 678 (138) ....................................................... 125

3.3.1 The attempted synthesis of ketal 173 ...................................................... 126

3.3.2 The attempted synthesis of epoxide 180 ................................................. 130

3.3.3 The Taylor synthesis of SDEF 678 (138) and speciosins A-F (139-144) .....

................................................................................................................. 131

3.3.4 The formal synthesis of SDEF 678 (138) ............................................... 133

3.4 Conclusions and future work .......................................................................... 135

Chapter 4 Studies into the Total Syntheses of Glaciapyrroles B and C ........................ 137

4.1 Introduction .................................................................................................... 139

4.1.1 An introduction to glaciapyrroles B and C ............................................. 139

4.1.2 Aims of research ..................................................................................... 140

4.2 The attempted synthesis of glaciapyrrole C (323) via a key Heck cross-

coupling reaction ....................................................................................................... 141

4.2.1 The Synthesis of acrylate 329 ................................................................. 142

4.2.2 The attempted synthesis of vinyl iodide 337 .......................................... 143

vi

4.2.3 The synthesis of vinyl bromide 348 ........................................................ 148

4.2.4 Attempted Heck cross-coupling between vinyl bromide 348 and acrylate

329 ................................................................................................................. 149

4.3 The attempted synthesis of glaciapyrrole B (322) via a key Heck cross-


4.3.1 The attempted synthesis of vinyl bromide 357 ....................................... 151

4.3.2 Attempted Heck reactions between vinyl bromide 357 and acrylate 329 .....

................................................................................................................. 154

4.4 The attempted synthesis of glaciapyrrole C (323) via a key Suzuki cross-


4.4.1 The synthesis of vinyl iodide 327 ........................................................... 156

4.4.2 The attempted synthesis of epoxy boronic acids and esters.................... 158

4.5 Conclusions and future work .......................................................................... 161

Chapter 5 Experimental Section ................................................................................... 163

5.1 General experimental ..................................................................................... 165

5.2 Experimental for Chapter 2 ............................................................................ 167



5.5 Biological evaluation experimental for Chapter 2 ......................................... 243

Chapter 6 Bibliography ................................................................................................. 245

Chapter 7 Appendix ...................................................................................................... 261

7.1 Crystal structures ............................................................................................ 263

7.1.1 General Information ................................................................................ 263

7.1.2 6-(Bromoethynyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-one

(275) ................................................................................................................. 263

7.1.3 (2Z)-3-iodo-1-[1-[(4-methylphenyl)sulfonyl]-1H-pyrrol-2-yl]but-2-en-1-

one (327) .............................................................................................................. 267

vii

Acknowledgments

I would like to start off by thanking my supervisor, Dr. Scott Stewart. Scott, thank you

for giving me the opportunity to be a part of your research group. I have really

appreciated the immense support, patience, encouragement, and invaluable guidance

you have provided me with throughout the years. I have enjoyed working with you, and

your constructive advice and assistance have been beneficial in the development of my

work. Also, your enthusiasm for chemistry is infectious. To my co-supervisors

Professor Emilio Ghisalberti and Professor George Yeoh, thank you for always being

available to me when I needed advice. I have learned a lot from you both. A special

thank you to Emil for his invaluable assistance in proof-reading my thesis.

I would also like to thank all the academic staff members of the School of Chemistry

and Biochemistry who I have learned a lot from throughout the years. Special mentions

go to Professor Bob Bucat who has been kind enough to let me use him as a referee for

job applications, and also to Professor Alan McKinley who has always been willing to

offer advice when needed.

To all the members of the Bayliss building staff, thank you so much for your assistance

and support. My work would not have been possible without your help. A big thank you

to Dr. Anthony Reeder for promptly running my mass specs, and to Dr. Brian Skelton

for acquiring all of my x-ray crystal structures. I would especially like to thank Dr.

Lindsay Byrne for taking the time to teach me about NMR, and for being fun to chat to.

Also, a huge thank you to Adrian and Gavin for helping me to obtain EE values.

A huge thank you also goes to all the members of the chemistry department that I have

worked with and gotten to know throughout the years. It has been wonderful getting to

know you all, and I am glad to be able to call many of you friends. A special mention

goes to Dr. Marta Polomska. Marta, thank you so much for taking the time to teach me

and be my friend when I was starting out. Starting out as an honour's student in an

established lab can be intimidating, but you made it a lot of fun.

To all the past and present members of the SGS/GAK lab: it has been amazing getting

to know you all and you have certainly made this experience an enjoyable one. Special

mentions go to Nikki Man Man, Sven, Becky, Ling, Carlos, Jackson, Mattheus, Evenda,

viii

Campbell, Nigel, and James for all of the good times in the lab. I would also like to

thank Elaine, Siobhan, Mitch, and Travis for all of the fun times eating cake.

To Mary and Jim Heath, you have both been a wonderful source of good wishes and

encouragement, which I truly appreciate. Jim, thank you so much for taking the time to

proof-read my thesis, I really appreciate the effort you put in.

To my best friends Asma and Fatima, you girls are amazing! Thank you for keeping me

sane throughout this experience with all of the incredibly fun times and laughs we have

shared together! Also, thank you for your words of love, support, and encouragement

which have meant so much to me. I love you both and can't wait to spend more time

with you guys in the future! Also, to Tina and all my other dear friends, thank you for

the good times and for being immensely supportive and encouraging!

To my darling and wonderful Charles Hamilton Heath (who I affectionately call

Chuck), the highlight of my PhD has been getting to know you, and sharing this

experience with you. My PhD experience would not have been as enjoyable without

you. You are one of the most incredible, amazing, loving, and caring people I know,

and I love you dearly. I can't thank you enough for all the love, support, encouragement,

and amazing times we have shared together. They have been the happiest of times, and

there will be many many more to come! I can't wait to spend more time with you!

Lastly, but certainly not least, to my incredible and most darling family, Thank You!!

To my wonderful Mum and Dad (Amarani and Cheemun, I couldn't ask for more

amazing parents) and to my amazing brothers (Leonard and Reggie, I couldn't ask for

more wonderful siblings) thank you so much for your constant unconditional love,

support, and encouragement. I would be nowhere in life today without your input. You

are the most incredible, amazing, caring, and loving family anyone could ever ask for,

and I couldn't have done this without you. I am especially grateful to my darling

Mummy for always checking on my well-being and constantly making sure I was well

fed, to my darling Dad for always encouraging me to reach for the stars, to my lovely

Leonard for always supporting me, and to my wonderful Reggie for all of his support

and help with the contents page. I don't have enough words to express the gratitude I

feel for you all. I love you all dearly, and can't wait to spend more time with you guys in

the future! Thank you for always believing in me.

ix

List of Abbreviations

δ chemical shift (parts per million)

μM micromolar

pi

σ-bond sigma-bond

~ approximately

°C degrees Celsius

6-APA (+)-6-aminopenicillanic acid

Å angstrom

Ac acetyl

aka also known as

AM1 Austin model 1

APCI atmospheric pressure chemical ionisation

app apparent

aq aqueous

Ar aromatic (generic)

BF3·Et2O boron trifluoride diethyl etherate

BMO Bestmann–Ohira

Bn benzyl

Br2BH.SMe2 dibromoborane-dimethyl sulfide

Bz benzoyl

CDT cell doubling time

conc. concentrated

Concn concentration

Cy2NMe N,N-dicyclohexylmethylamine

d doublet

dba dibenzylideneacetone

DBP dibutyl phthalate

DBU l,8-diazabicyclo[5.4.0]undec-7-ene

dd doublet of doublets

DEPT distortionless enhancement by polarization transfer

x

DET diethyl tartrate

DIBAL-H diisobutylaluminium hydride

DIT diisopropyl tartrate

DMAP 4-(N,N-dimethylamino)pyridine

DMDO dimethyldioxirane

DME 1,2-dimethoxyethane

DMF dimethylformamide

DMP Dess–Martin periodinane

DMSO dimethyl sulfoxide

dppf 1,1' -bis(diphenylphosphino)ferrocene

EI electron impact

eq equivalent(s)

et al. et alii (from Latin meaning "and the rest")

Et2O diethyl ether

EtOAc ethyl acetate

EtOH ethanol

FAB fast atom bombardment

h hour(s)

HB catalyst Herrmann-Beller catalyst

HBV hepatitis B virus

HCC hepatocellular carcinoma

HCV hepatitis C virus

HMPA hexamethylphosphoric triamide

HPLC high-performance liquid chromatography

HPLC-PDA high performance liquid chromatography with photodiode

array

HRMS high-resolution mass spectrometry

Hz hertz

i iso

i-BuZnBr isobutylzinc bromide

i-PrMgBr isopropylmagnesium bromide

IBX 2-iodoxybenzoic acid

IC50 the half maximal inhibitory concentration

xi

IGF-II insulin-like growth factor 2

IR infrared

J coupling constant (in NMR spectrometry)

KNaC4H4O6.4H2O potassium sodium tartrate aka Rochelle's salt

LDA lithium diisopropylamide

LiHMDS lithium bis(trimethylsilyl)amide

LPC liver progenitor cells

M molar

m multiplet

m meta

m.p. melting point

m-CPBA meta-chloroperoxybenzoic acid

MeOH methanol

min minute(s)

Na2(EDTA) ethylenediaminetetraacetic acid disodium

Na2B4O7 borax

NaHMDS sodium bis(trimethylsilyl)amide

NBS N-bromosuccinimide

n-BuLi n-butyllithium

NMR nuclear magnetic resonance

NR no reaction

o ortho

OTf trifluoromethanesulfonate

p para

p-CH3OC6H4MgBr para-methoxyphenylmagnesium bromide

Ph phenyl

Ph2O diphenyl ether

PhI(OAc)2 (diacetoxyiodo)benzene aka phenyliodonium diacetate

PIDA (diacetoxyiodo)benzene aka phenyliodonium diacetate

PIL p53 immortalised liver

PPh3=O triphenylphosphine oxide

PPh3Br2 bromotriphenylphosphonium bromide

xii

ppm part(s) per million

P(t-Bu)3HBF4 tri-tertiary-butylphosphonium tetrafluoroborate

p-TsCl para-toluenesulfonyl chloride

p-TsOH para-toluenesulfonic acid

q quartet

Rf retention factor (in chromatography)

rt room temperature

s singlet

SAR structure–activity relationship

sept septet

SN2 bimolecular nucleophilic substitution

t triplet

t or tert tertiary

TBAF tetrabutylammonium fluoride

TBDMS tertiary-butyldimethylsilyl

TBDMSCl tertiary-butyldimethylsilyl chloride

t-BHP tertiary-butyl hydroperoxide

TBS tertiary-butyldimethylsilyl

t-BuLi tertiary-butyllithium

TFA trifluoroacetic acid

TFAA trifluoroacetic anhydride

THF tetrahydrofuran

TLC thin-layer chromatography

UV ultraviolet

VO(acac)2 vanadyl acetylacetonate

w/w weight per unit weight (weight-to-weight ratio)

ZINDO Zerner parameterization of intermediate neglect of differential

overlap

xiii

1

Chapter 1

General Introduction

2

3

1.1 Natural products as synthetic targets

Natural products - compounds that are produced naturally by living organisms - have

piqued the curiosity of mankind for millennia due to their fascinating biological

activities and diverse applications.7 They have often been the sole means to treat

diseases and injuries, and their use for medicinal purposes predates recorded human

history.8-10

In fact, palaeoanthropological studies have suggested, as evidenced from

findings in archaeological cave sites at Shanidar, in Kurdistan, Iraq, that Neanderthals

might have been aware of the medicinal properties of various plants more than 60,000

years ago.11

Throughout human history, nearly every civilization has accumulated

experience with and acquired knowledge of natural products.8 This has led to important

advancements in the fields of medicine, agriculture, the physical sciences, and

industry.8,12-14

Despite the fact that natural products have been used for millennia, it was not until the

synthesis of urea in 1828 by Friedrich Wöhler that it was believed that compounds

derived from living organisms could be synthesised in a lab (Scheme 1.01).15

The

synthesis of urea contradicted the widespread concept of vitalism which hypothesised

that organic compounds possessed a vital force that made their synthesis without

biological starting materials impossible.12

Scheme 1.01. In 1828 Friedrich Wöhler synthesised urea by treating silver isocyanate with ammonium

chloride, discrediting the concept of vitalism.15

In addition to the excitement and interest associated with the challenges that come from

attempting to synthesise their highly varied and often complex structures, there are also

many practical reasons for using natural products as synthetic targets.16-19

For instance,

before the advent of powerful analytical techniques, such as NMR spectroscopy and

X-ray crystallography, the purpose of total synthesis was to confirm the structure of a

natural product.20

4

A classic example of this is the structural elucidation of the historically interesting

alkaloid poison strychnine (1) (Figure 1.01).21-23

In the absence of modern

spectroscopic techniques, it took nearly 130 years of arduous chemical degradation and

derivatisation reactions to finally determine its structure.24,25

Additionally, many of the

reactions and techniques employed by researchers to elucidate the structure of

strychnine became important developments in their own right.23

This latter fact

highlights another benefit of the study and synthesis of natural products: as a principle

driving force for discovery that has led to rapid advancements and the development of

knowledge in the field of organic chemistry.16-19

Figure 1.01. Strychnine (1), a poison isolated by Pelletier and Caventou in 1818 from the beans of

Strychnos ignatii and Strychnos nux-vomica.21,22

Natural products provide the ultimate synthetic challenge because, unlike designed

molecules, they have distinct structures that need to be replicated exactly. The need for

exact replication of a natural product, despite the complexity of its structure has, in

many cases, led to advances in reaction methodology. For example, in the 1950s,

research efforts directed towards the syntheses of penicillins led to a considerable body

of knowledge regarding the construction of substituted β-lactams (Figure 1.02).26

In

addition, penicillin research also provided momentum for the development of

carbodiimide based reagents for the formation of peptide bonds.27

Figure 1.02. (+)-6-Aminopenicillanic acid (6-APA) (2), the core structure of the penicillins.26

The study of natural products has also contributed to the development of chemical

knowledge and to greater understandings of underlying physical principles. An example

5

of this is the discovery of chirality in organic compounds by Louis Pasteur in 1848 from

his study of tartaric acid.12,28

Natural products also play a key role in the pharmaceutical industry.8,9,29-37

As discussed

earlier, natural products derived from plants, animal, and fungi have been used as

medicines for millennia.8 However, many contemporary pharmaceuticals are also

natural products based.8,9,29-39

Additionally, laboratory synthesis is often the only

feasible method to obtain natural products in adequate quantities when the supply of a

natural source is limited or if the bioavailability of a natural compound is low. For

example, the highly effective chemotherapeutic drug paclitaxel can be isolated from the

pacific yew tree (Taxus brevifolia), but only in sparse quantities (Figure 1.03).40

Figure 1.03. Paclitaxel (3) aka taxol.40

It requires the paclitaxel from six 100-year-old trees to treat one patient,41

and

because the Pacific yew tree is scarce harvesting of the trees was never a feasible option

to obtain taxol for commercial use. Instead, the use of taxol was enabled by the

development of a semi-synthetic pathway beginning with a natural compound

(10-deacetylbaccatin III) isolated from an alternative commercially harvestable species,

the European yew tree (Taxus baccata).42,43

Included in Nature's diverse array of molecular structures are the following classes of

compounds: polyketides, carbohydrates, oxygen heterocycles, aromatics,

benzofuranoids, aliphatics, benzopyranoids, flavonoids, tannins, lignans, terpenoids,

steroids, amino acids, peptides, polypyrroles, and alkaloids. Some examples

highlighting the highly varied structures of natural products are shown in Figure 1.04.7

6

Figure 1.04. Natural product examples showing highly varied structures: the steroid testosterone (4);44

the terpenoid mevalonic acid (5);45

and the alkaloid morphine (6).46

Due to their ingenious molecular structures and fascinating biological activities, it is

clear that the discovery, study, and synthesis of natural products will continue to play a

fundamental role in the evolution of organic chemistry, biology, pharmacy, industry

(fine chemical), and medicine.

7

1.2 Palladium-catalysed reactions in natural product synthesis

It is through the assembly of carbon atoms that complex molecules can be created.

Thus, the ability to form carbon-carbon bonds is the most important transformation for

synthetic chemists in the synthesis of natural products. In the last half century, transition

metal compounds have been shown to activate various organic compounds and catalyse

the formation of new carbon-carbon bonds.47,48

Organopalladium compounds in

particular have been noted as useful catalysts since the discovery of the Wacker

oxidation in 1959.*†49,51

The ability to "couple" two molecules together is a powerful

synthetic tool and has had an immense impact on the synthesis of pharmaceutical drugs,

the synthesis of industrial materials, industrial chemical processes, and academic

research.50-52

The important role of palladium catalyses in contemporary organic

chemistry was even recognised in 2010 by the rewarding of Heck, Negishi, and Suzuki

with the Nobel prize for chemistry for their work on "palladium-catalysed cross-

couplings in organic synthesis".

As the work in this thesis is linked by the central theme of palladium-catalysed cross-

coupling reactions as key steps in the total syntheses of natural products and their

derivatives, this introduction will aim to give a brief overview of the area. In particular,

the introduction will discuss the key cross-coupling protocols i.e. the Negishi, Suzuki,

Sonogashira, and Heck reactions, utilised in this work.

1.2.1 Palladium-catalysed cross-coupling reactions

The phrase "palladium-catalysed cross-coupling" is a blanket term for a variety of

reactions that link two fragments together with a new carbon-carbon bond on palladium

via the formation and breakdown of metal-carbon bonds.50

There exist two general

types of cross-coupling reaction (Scheme 1.02).50

In both reaction types an organic

halide or triflate of the type R1X is the electrophilic coupling partner and both reactions

are catalysed by zerovalent palladium.50

The oxidative addition of a zerovalent

* The Wacker reaction involves oxidation of ethylene to acetaldehyde in the presence of a palladium-

catalyst, normally PdCl2.49

† The factors responsible for rendering palladium as a superior catalyst component are discussed in detail

by Negishi et al.50

8

palladium complex to the electrophilic halide or triflate is thought to be the first step in

both types of cross-coupling reaction.50

R1 = acyl, aryl, benzyl, vinyl

R2 = alkyl, alkynyl, aryl, vinyl

X = halide, triflate

Scheme 1.02. The two types of palladium-catalysed cross-coupling reactions.50

The two different types of cross-coupling reaction vary chiefly in the type of

nucleophilic coupling partner used. The first reaction type (equation 1, Scheme 1.02)

uses an organometallic compound (R2M) whereas the second type (equation 2,

Scheme 1.02) uses an olefinic species. The two different reaction types have two

distinct mechanisms. The Negishi, Suzuki, and Sonogashira reactions, which all use

organometallic nucleophilic coupling partners, follow the same type of mechanism

involving a key transmetalation step.50,53-60

Whereas, the Heck reaction, which uses an

olefin containing coupling partner, occurs via an alternate mechanism.50,61-64

1.2.2 Palladium(0)-catalysts and electrophilic coupling partners

Before the Negishi, Suzuki, Sonogashira, and Heck cross-couplings are discussed in

more detail individually, it is deemed pertinent to discuss the active catalytic species

and electrophilic coupling partners mutual to this group of reactions. For the previously

mentioned reactions, catalysis is thought to be initiated by a co-ordinately unsaturated

14-electron, zero-valent palladium species, Pd0L2. There are three main ways to form

this active species: by ligand dissociation from a coordinatively saturated zero-valent

palladium complex in the form of Pd0L4 (equation 1, Scheme 1.03);

65,66 from ligand

exchange between a stable palladium(0) complex and a reactive phosphine (equation 2,

Scheme 1.03);67,68

and from the reduction of a palladium(II) complex in situ by an

additive such as a phosphine (equation 3, Scheme 1.03).69,70

The nature of the Pd(0)

9

active species for equation 3 is yet unknown, however studies have indicated that the

active species is an anion of the type [Pd(PPh3)2(OAc)]-.71

Scheme 1.03. Examples for the formation of active palladium(0) species.65-71

Organic halides and triflates are generally used as electrophilic coupling partners in

cross-coupling reactions because they are reactive towards palladium(0) complexes. In

simple terms, the reaction between a palladium(0) complex and an electrophilic

coupling partner is thought to be a nucleophilic attack by an electron rich zero-valent

metal on an electron poor organic compound.50

The insertion of a palladium atom

between a carbon-halide bond is referred to as oxidative addition and it is thought to be

the rate-limiting step in a catalytic cycle. Oxidative addition can be facilitated by the use

of electron-withdrawing substituents on the organic halide or triflate, or by the use of

electron-rich ligands on palladium to increase its nucleophilic character.50

Reactive organic halides and triflates include acyl, benzyl, alkenyl, alkynyl and aryl

compounds. The approximate order of reactivities for organic halides and triflates is as

follows: I > OTf > Br > Cl >> F.50

The order of reactivity is opposite to that of SNAr

reactions because the reactivity of the organic electrophile has less to do with the

polarity of the C-X bond and more to do with the stability of the leaving group.50,72

Recent studies have suggested that aryl tosylates, mesylates, and imidazolylsulfonates

are also viable electrophilic coupling partners.73

1.2.3 The general mechanism for the Negishi, Suzuki, and Sonogashira cross-

coupling reactions

In the Negishi, Suzuki, and Sonogashira cross-coupling reactions organozinc,

organoboron, and cuprous acetylide organometallic compounds, respectively, are

10

coupled with organic electrophiles in the presence of zerovalent palladium.50,51,53,74

The

reactions lead to the formation of new C(sp3)-C(sp

2), C(sp

2)-C(sp

2), or C(sp

1)-C(sp

2)

bonds. The general mechanism for the palladium-catalysed cross-coupling reaction

between an organic electrophile and an organometallic nucleophile is outlined in

Scheme 1.04.50

Scheme 1.04. The general mechanism for the palladium-catalysed cross-coupling reaction between an

organic electrophile and an organometallic nucleophile.50,54

The first step in the Negishi, Suzuki, and Sonogashira cross-coupling reactions is the

oxidative addition of an organic electrophile R1X to the zerovalent palladium catalyst

[Pd0Ln]. This involves the breaking of a carbon-halogen σ-bond, the formation of a

palladium-carbon σ-bond, and the formation of a palladium-halogen σ-bond. The

oxidation state of palladium is raised by two as it effectively inserts between the carbon

and halogen. In the next step, the organic group on the organometallic nucleophile R2M

is transferred to the palladium in a transmetalation process. As a result of

transmetalation, the two organic groups R1 and R2 are assembled on the same palladium

centre via palladium-carbon bonds. In the last step, the R1 and R2 groups couple with

one another, after they are cis-oriented on palladium, to give a new carbon-carbon

11

single bond. The product R1R2 is then released from the palladium atom in a step called

reductive elimination. The nomenclature is derived from the change in oxidation state of

palladium from +2 back to 0 upon release of the product and continuation of the

catalytic cycle.50

Each reaction type is discussed in more detail individually below.

1.2.4 The Negishi reaction

A Negishi reaction, proposed by Ei-Ichi Negishi in 1977, refers to a palladium- or

nickel-catalysed cross-coupling reaction between an organozinc compound and an

electrophilic coupling partner (Scheme 1.05).53,74

Organozinc reagents exhibit high

reactivity in palladium-catalysed cross-coupling reactions, and the Negishi reaction

displays some of the widest synthetic scope of all the various cross-coupling protocols

involving organometallic reagents.50,51

R1 = acyl, aryl, benzyl, vinyl



Y = Cl, Br, I

Scheme 1.05. Simplified summary of the Negishi reaction.

The organic group on the organometallic nucleophile R2ZnY can be alkyl, alkynyl, aryl

or vinyl in nature (Scheme 1.05).51

Hence, the reaction is able to catalyse C(sp1)–

C(sp2), C(sp

2)–C(sp

2), and C(sp

2)–C(sp

3) bond forming processes. Especially significant

is the reaction's ability to enable the formation of the C(sp2)–C(sp

3) bond, an uncommon

but synthetically useful transformation in the area of cross-coupling protocols. The

major drawbacks of the Negishi cross-coupling are the lack of chemoselectivity (due to

the reactivity of many common functional groups in the presence of organozinc

coupling partners) and the sensitivity of organozinc reagents to air and water. It is for

these latter reasons, that the Negishi coupling has been relatively under-utilised in

comparison to the Suzuki and Stille reactions despite the fact that the use of organozinc

reagents predates the development and use of both organoboranes and organostannanes

in cross-couplings.51,53,56,75

12

Despite its history of being under-utilised, there has been a recent surge in the

development and use of the Negishi protocol.51

This resurgence has been fuelled by the

recognition that organozinc compounds are highly reactive, readily accessible from

cheap starting materials, and have a low toxicity.76,77

Additionally, the by-products of

the reactions are usually zinc salts that are easily separated from the product via aqueous

workup or standard purification techniques.53

Organozinc compounds are typically prepared from either the direct insertion of zinc

metal into organic halides, or from other organometallic precursors via a transmetalation

process.78-81

Additionally, because organozinc reagents have such a high reactivity,

standard substrate reactions are usually successful in THF, at room temperature, in the

presence of Pd(PPh3)4, PdCl2(PPh3)2, or PdCl2(dppf).50,51

On the other hand, more

rigorous and carefully optimised conditions with added reagents, higher temperatures,

or more reactive and expensive catalysts are required for reactions involving their

relatively less reactive organoborane and organostannane counterparts.50,51

Despite the positive aspects, the high reactivities of organozinc compounds also have

some drawbacks. Due to their high reactivities, organozinc compounds are mostly

unstable when exposed to water, alcoholic solvents, or air. This precludes their use in

palladium-catalysed reactions under aqueous or protic conditions. Additionally, they

cannot be tolerated by a wide range of functional groups such as acyl halides,

aldehydes, hydroxyls, or carboxylic acids.50

Despite this, the Negishi protocol has wide

ranging applicability and is a popular procedure due to its operational simplicity, low

toxicity, and wide synthetic scope. The synthesis of discodermolide depicted in

Scheme 1.06 displays the special ability of the Negishi protocol to enable the formation

of a C(sp2)–C(sp

3) bond.

82,83

13

Scheme 1.06. The Negishi cross-coupling reaction as a

key step in the synthesis of the natural product discodermolide.

Reagents and conditions: a) Pd(PPh3)4 (5 mol%), Et2O, 20°C, 66%.51,82,83

1.2.5 The Suzuki reaction

A cross-coupling reaction between an organoboron compound and an electrophilic

coupling partner in the presence of a base, and a palladium catalyst, is known as a

Suzuki reaction (Scheme 1.07).56,57,59,84

R1 = alkynyl, aryl, benzyl, vinyl



Scheme 1.07. Simplified summary of the Suzuki reaction.50,51

Organoboron coupling partners are highly stable, tolerate a wide range of functional

groups, are highly chemoselective, readily accessible, and cross-couple under mild

reaction conditions.84-86

Additionally, organoboron compounds are generally non-toxic

and the other product of the reaction, boric acid, is generally easy to separate from the

product via standard purification techniques.85,87

These reasons have made the Suzuki

reaction popular in the pharmaceutical industry, chemical industry, and academic

research.51,58,88

14

Like the Negishi reaction, the Suzuki reaction is used to catalyse a variety of carbon-

carbon bond forming reactions including C(sp1)–C(sp

2), C(sp

2)–C(sp

2), and C(sp

2)–

C(sp3) bonds.

50,89,90 The key difference between the reactions is that the organoboron

coupling partner in the Suzuki reaction is activated with base before

transmetalation.50,54,91

Oxy bases such as NaOH and NaOMe are best at accelerating the

coupling reaction.91

It is believed that the base facilitates transmetalation via a more

nucleophilic organoboronate complex 12 (Scheme 1.08).86,91

Scheme 1.08. Base-assisted transmetalation in the Suzuki reaction.91

Due to the fact that bases are an essential component of the Suzuki cross-coupling

reaction, the chemoselectivity of the reaction must also include that of the added base.

The reaction conditions involving PdCl2(dppf), and aqueous NaOH in THF works well

in most cases.50

However weaker bases are often used if the substrates are highly

functionalised or sensitive to strong bases.92

A major drawcard for the Suzuki reaction is the ready accessibility of organoboron

coupling partners for cross-coupling.58

Due to the prominent role of the Suzuki reaction

in organic chemistry, boronic acids and esters are readily available from commercial

sources. In addition, a lot of research has also been invested into their efficient and mild

synthesis.84,85,93

The many methods of accessing boronic acids and esters are discussed

thoroughly in an excellent review by Hall.85

The two most common methods of

accessing boronic acids and esters are by the electrophilic trapping of lithiated

intermediates following lithium-halogen exchange with a halide (equation 1, Scheme

1.09) or by the cross-coupling reaction between an aryl or vinyl halide with a diboronyl

reagent (equation 2, Scheme 1.09).85,94

15

R = alkyl, alkynyl, aryl, benzyl, vinyl


Y = OR

Scheme 1.09. Two examples for the synthesis of organoboron coupling partners.85

The Suzuki reaction holds a prominent role in total synthesis because of its reliability,

high stereo-specificity, and because it occurs under mild reaction conditions. The

particular usefulness of the Suzuki reaction in the synthesis of a highly conjugated

aromatic compound (18) is presented in Scheme 1.10. Compound 18 is a precursor to

the natural product michellamine B.95

Scheme 1.10. The Suzuki cross-coupling reaction as a

key step in the synthesis of the natural product michellamine B.

Reagents and conditions: a) Pd(PPh3)4, K3PO4, DMF, 90°C, 76%.51,95

1.2.6 The Sonogashira reaction

A cross-coupling reaction between a terminal alkyne and an organic electrophile in the

presence of a copper(I) co-catalyst, a base, and a palladium-catalyst is referred to as a

Sonogashira reaction (Scheme 1.11).60

16

R1 = aryl, benzyl, vinyl

R2 = alkyl, aryl, benzyl, vinyl


Scheme 1.11. Simplified summary of the Sonogashira reaction.50

The palladium-catalysed coupling of terminal alkynes with vinyl or aryl halides was

initially developed by the groups of Heck and Cassar.96,97

However, it was Sonogashira

and co-workers that discovered that addition of a copper(I) salt could accelerate the rate

of the reaction.60,98

The Sonogashira reaction is now the most widely used palladium-

catalysed method to access substituted alkynes in total synthesis.51,60,99,100

The Sonogashira reaction occurs via the same general mechanism described for the

Negishi and Suzuki cross-coupling reactions (Scheme 1.04). That is, oxidative addition

followed by transmetalation, and reductive elimination to give a coupled product.

However, the Sonogashira reaction differs from the other reactions in that the

organometallic nucleophile, in this case a copper(I) acetylide, is formed in situ from a

terminal alkyne with the aid of a copper(I) co-catalyst and a base.101

The additional

process is catalytic because the copper(I) halide is regenerated after transmetalation of

the copper acetylide (Scheme 1.12).101

R1 = aryl, benzyl, vinyl

R2 = alkyl, aryl, benzyl, vinyl


Scheme 1.12. Transmetalation in the Sonogashira reaction.101

17

The mild reaction conditions, which can occur at room temperature, with mild bases,

has allowed for the use of the Sonogashira cross-coupling protocol in the total synthesis

of many complex molecules.102-104

The reaction provides a valuable method for the

synthesis of acetylenic compounds which are used in a wide range of applications

including the synthesis of pharmaceuticals, natural products, and designed molecules.

Shown below is an example of the Sonogashira reaction being used as a key step in the

total synthesis of the natural product disorazole C1 (Scheme 1.13).105

Scheme 1.13. The Sonogashira cross-coupling reaction as a

key step in the synthesis of the natural product disorazole C1.

Reagents and conditions: a) PdCl2(PPh3)2, NEt3, CuI, MeCN, -20°C, 94%.51,105

1.2.7 The Heck cross-coupling reaction

The coupling of an olefin with an aryl or vinyl halide or triflate, in the presence of a

palladium catalyst and a base, to give a substituted alkene, is referred to as a Heck

reaction (Scheme 1.14).106-111

R1 = aryl, vinyl

X1 = halide, triflate

Scheme 1.14. Simplified summary of the Heck reaction.50,51

18

The Heck reaction is an extremely efficient method for C(sp2)-C(sp

2) bond formation

and total synthesis has benefited remarkably from its development.112-114

The

application of the Heck reaction in total synthesis has enabled the attachment of side

chains, polyene construction, fragment couplings, and ring-closing reactions via inter-

and intra-molecular coupling reactions.115-121

The key steps of the catalytic cycle for the Heck reaction are illustrated in Scheme 1.15.

The reaction begins when the electrophilic coupling partner reacts with the active

palladium(0) species and oxidative addition occurs to provide a palladium(II) halide

complex, LnPdR1X. In the next step, the olefin coordinates weakly to the palladium (the

olefin must contain at least one hydrogen). Electron-deficient terminal olefins with

electron-withdrawing substituents are generally the most successful coupling partners

for the Heck reaction. After coordination, the R1 group on the palladium atom migrates

to one of the carbons of the co-ordinated olefin. This step, referred to as syn-insertion,

generates the carbon-carbon bond. The product of the syn-insertion then undergoes

internal rotation to bring a β-hydrogen into a position syn to the palladium atom.

Finally, the release of the product occurs after β-hydride elimination takes place and the

product alkene dissociates from the palladium complex. The zerovalent catalyst is

regenerated after the palladium(II) complex reacts with the base to form a salt

(Scheme 1.15).61

19

Scheme 1.15. The key steps of the proposed catalytic cycle for the Heck reaction.61-64

The β-hydride elimination step is responsible for the stereochemistry of the product

alkene. The mechanism of the reaction is considered to be a concerted syn-process

which occurs through a four-membered transition state (22 or 24). For this to occur the

insertion complex 23 must be able to rotate or adopt a conformation where a β-hydrogen

is aligned syn to the palladium(II) along the C-C axis. The elimination is reversible and

generally gives the thermodynamically more stable trans-alkene (Scheme 1.16).119

20

Scheme 1.16. β-hydride elimination.119

The Heck reaction has excellent versatility and functional group tolerance, for these

reasons it has been used in many total syntheses of complex molecules and still remains

a thriving area of research. One example showing the effectiveness and selectivity

of the Heck reaction in total synthesis is the enantioselective synthesis of estrone by

Tietze et al. (Scheme 1.17).122

Tietze's synthesis of estrone incorporates two Heck

cross-coupling reactions to establish the characteristic arrangement of four rings

observed in the natural product.122

Scheme 1.17. The Heck reaction in the enantioselective total synthesis of estrone by Tietze et al.122

Reagents and conditions: a) Pd(OAc)2, PPh3, DMF/MeCN/H2O, Bu4NOAc, 70°C, 50%; b) HB catalyst,

DMF/MeCN/H2O (5:5:1), Bu4NOAc, 115°C, 99%.51,122

21

Chapter 2

The Total Syntheses of Antrodia camphorata Natural Products and

their Derivatives for Biological Evaluation

22

23

2.1 Introduction

2.1.1 Natural compounds as a source of pharmaceutical agents

Drug discovery and development has long been an area of substantial research because

of the desire to bring safe and effective treatment to patients suffering from intractable

diseases.123

In modern-day drug development, there are two main methods of drug

discovery: phenotypic-based drug discovery, also known as classical pharmacology;

and target-based drug discovery, also known as reverse pharmacology.123,124

In classical pharmacology, most drugs are discovered through identification of the

active natural compounds isolated from natural sources.31,125,126

These compounds are

then screened in vitro in cellular models, or in vivo in animal models, to identify the

substances that have a desirable therapeutic effect.127

Once an active "hit" or "lead"

compound is identified, an effort is made to elucidate the mode of action to determine

the biological target of the compound.128

Additionally, the therapeutic effects of "lead"

compounds from natural sources can be improved when complemented with SAR

studies, high-throughput screening protocols, combinatorial chemistry, or computational

chemistry.29

An advantage of classical pharmacology over reverse pharmacology is that

the therapeutic impact in a given disease state is more promptly identified.36

In the early

era of drug discovery, classical or phenotypic-based pharmacology was the preferred

method for the identification of lead compounds.129,130

In recent years, with the advance of genomic research, there has been a shift towards

target-based drug discovery.131

Target-based drug discovery is based on the idea that

high-throughput screening of compounds can identify molecules that bind to and

modify various protein/receptor targets that are involved in disease

pathogenesis.36,124,132

Afterwards, these compounds can be tested in vitro or in vivo in

cellular and animal models to see if they have the desired therapeutic effects. A

disadvantage of the target-based approach is that it takes a longer time to establish a

connection between a protein or receptor target associated with a disease state and a

therapeutic effect, if there is any at all.130

Thus, despite the advances made in target-based reverse pharmacology,36

studies have

shown that classical pharmacology and natural compounds still play a more significant

24

role in drug discovery with more than half of new drugs coming from, or being derived

from, a natural source.29,31,35,37

In the case of anticancer agents, the proportion of drugs

that are natural compounds (or derived from them) is even more pronounced (>60%).133

The huge structural diversity, underlying biological effects, and novel modes of action

of natural products often goes beyond what scientists can design.133

Hence, it is not

surprising that natural products have been such a rich source of pharmaceutical

agents.8,9,30,31,33,38,123,132,134

In particular, tribal indigenous medicines or traditional remedies, nearly all of which are

obtained from natural sources, provide an excellent platform for finding compounds

with novel biological activity and potentially new modes of action.1,135,136

One such

source of bioactive natural products that has attracted attention as a potential source of

drug candidates is the medicinal fungus Antrodia camphorata.1,137-139

2.1.2 Natural products and potential anticancer agents from Antrodia

camphorata

Antrodia camphorata is a rare parasitic fungus that grows only on the endangered

Taiwanese tree species Cinnamomun kanehirai.1 This highly sought-after fungus and its

extracts have been used in traditional Chinese and Taiwanese medicine as remedies for

inflammation, abdominal pain, food and drug intoxication, hypertension, and, most

interestingly, for liver cancer.1,137,140

A range of compounds including steroids,

diterpenes, triterpenoids, benzenoids, sesquiterpene lactones, and polysaccharides have

been isolated from Antrodia camphorata and many have exhibited biological

activity.141,142

We were particularly interested in five unique maleic anhydride and maleimide natural

products (31-35) that were isolated from the mycelium of Antrodia camphorata

(Figure 2.01).1 The first three natural products (31-33) were isolated by Nakumara et al.

and showed cytotoxic activity against Lewis Lung carcinoma (LLC) cell lines.1 The

next two structurally related compounds (34 and 35) were isolated by Wu et al. and

showed nitric oxide inhibition, which leads to anti-inflammatory activity.2

25

Figure 2.01. Maleic anhydride and maleimide natural products 31-35 isolated from the mycelium of

Antrodia camphorata.1,2

As stated earlier, the extract of Antrodia camphorata has widely been cited as a

treatment for liver cancer and has more recently been shown to decrease cell growth and

induce apoptosis in two human liver cancer cell lines.137

Despite this, no additional

biological evaluation studies have been conducted on liver cell lines. As a result, we

were particularly interested in seeing if the natural products 31-35 would show

independent biological activity when tested against tumourigenic liver cell lines. Our

interest in natural products that target liver cells stemmed from a desire to find a

bioactive natural product or derivative that might suppress tumourigenic liver cell

numbers as a potential way to treat hepatocellular carcinoma (HCC). Currently, the only

chemotherapeutic way to treat HCC is through treatment with the Bayer-produced

pharmaceutical drug sorafenib (36) (Figure 2.02).143-145

Figure 2.02. Sorafenib (36).

26

2.1.3 Biological studies of Antrodia camphorata natural products 31-35 and their

derivatives as potential therapeutic agents for liver cancer

Hepatocellular carcinoma (HCC), a type of liver cancer, is one of the most common

causes of cancer death. HCC frequently arises from damage to the liver caused by

certain pathologies such as alcoholic liver disease, hepatitis B virus (HBV) infection, or

hepatitis C virus (HCV) infection.146

A common feature of HCC is the significantly

elevated presence of inflammatory cells and liver progenitor cells in the liver.147

Therefore, as stated earlier, our research interests were aimed at finding bioactive

natural products or derivatives that might effectively suppress tumourigenic LPC

numbers as a potential way to treat hepatocellular carcinoma.148

Our study was a typical phenotypic-based investigation to identify a potential anticancer

lead from a simple dose-dependent phenotypic change assay on liver cell lines. The

liver cell lines used for our study were tumourigenic liver progenitor cells (PIL2) and

non-tumourigenic liver progenitor cells (PIL4) generated from cells originally isolated

from the p53 knockout mouse.149,150

PIL is an acronym for p53 immortalised liver. The

term p53 refers to a specific protein used to help regulate different stages of the cell

cycle and apoptosis.151-154

The absence of the p53 protein, in addition to other genetic

alterations, renders a cell immortalised because it allows a cell to cycle past the

Hayflick limit, which is the limited number of cellular divisions a cell undergoes before

it senesces.149,150,155

By using immortalised cell lines, changes to the cell can be

attributed to alterations by the added compound rather than death by natural apoptosis.

Studies have shown that PIL2 cells can be classified as tumourigenic because they are

high in the gene cIAP1, an inhibitor of apoptosis, a trait common to most cancer

cells.149

Also, the PIL2 cells posses a higher relative mitochondrial membrane potential

relative to PIL4 cells, another trait common to most cancer cells.149

The most successful

chemotherapeutic agents are the ones that will selectively target carcinomas cells over

normal cells. By using both tumourigenic and non-tumourigenic cell lines, we aimed to

establish whether any of the natural products and their derivatives showed any

specificity in activity.

27

2.1.4 An introduction to the chemistry of maleimides and maleic anhydrides

Maleimides are a sub-class of imide also referred to as cyclic monoimides.156

The term

maleimide refers to a compound that contains an imide that is part of a five membered

heterocyclic ring and that also contains an alkene subunit (Figure 2.03).157,158

In regards

to reactivity, the maleimide ring is active both at the imide functional site and the

alkene.156,157,159-163

In addition, each of these groups exerts an influence on the other

meaning that a maleimide reacts very differently to a typical cyclic monoimide or cyclic

olefin.156

Figure 2.03. The maleimide functional group (37).

Maleimides are prevalent in nature in many diverse structural forms.1,164-166

Furthermore, maleimide natural products are generally bioactive.2,164,167

Besides being

naturally available, they are also synthesised by design for pharmacological use, and as

precursors in industrial processes.163,168-170

They have found a wide range of use as

enzyme inhibitors, cross-linking reagents in polymer chemistry, and reactive

dienophiles in Diels-Alder cycloadditions.168

Also, natural product maleimides and

synthetically derived maleimides are both frequently tested for their activity as

phytotoxic agents, antitumor agents, antifungal agents, antibacterial agents, and

antimitotic agents.169

Maleimides are synthesised from maleic anhydrides via nucleophilic substitution by an

amine, followed by dehydration with concomitant ring-closure (Scheme 2.01).156,171-173

28

Scheme 2.01. The synthesis of a maleimide from a maleic anhydride.

Maleic anhydrides and maleimides are inter-convertible and one is often accessed from

the other. Maleic anhydrides are a sub-class of cyclic anhydride (Figure 2.04).156,174

Like maleimides, maleic anhydrides are reactive dienophiles in Diels-Alder

cycloadditions, show a diverse range of biological activities, and have wide ranging

industrial applications.175

It should be noted that maleic anhydrides can also be easily

hydrolysed to their maleic acid derivatives.

Figure 2.04. The maleic anhydride functional group (38).

2.1.5 Proposed synthesis

As discussed earlier, chemical synthesis is often the only feasible way to obtain large

quantities of natural products for further biological evaluation. The natural product

maleic anhydrides and maleimides 31-35, isolated from the fungus Antrodia

camphorata, were no exception. Due to the highly sought after medicinal properties of

this fungus, it has been oversampled from the wild and is now endangered.176

Combined

with the fact that cultivation attempts have failed, large amounts of the fungus are

difficult and expensive to obtain.176

Thus, chemical synthesis is the only way to obtain

larger quantities of the natural products (31-35) for further biological activity

29

screenings. As a result, we required an efficient method to obtain natural products 31-35

and their various structural derivatives for structure-activity relationship studies (SAR).

At the time of this study, there were only two literature methods for the syntheses of

Antrodia camphorata natural products 31-33.166,177

One was a seven-step linear

sequence by Argade et al.177

(Scheme 2.02) and another was a more convergent five-

step synthesis by our group, Stewart et al.166

(Scheme 2.03). As the synthesis of a

number of structural derivatives for SAR studies was a key part of our investigation, we

needed a synthesis that would allow us to efficiently and easily vary the attachments at

the C3 and C4 positions of the heterocyclic core (Figure 2.01).

30

Scheme 2.02. Argade synthesis of Antrodia camphorata natural products 31-34.177

Reagents and conditions: a) p-CH3OC6H4MgBr (1.5 eq), THF, HMPA, –20°C, 0.5 h, 73%; (b) (i) LiOH

(10 eq), THF/H2O (3:1), rt, 18 h, (ii) 1 M aq HCl, 92%; (c) Ac2O, reflux, 1.5 h, ~ 100%; (d) NBS (1.5 eq),

DBP (10 mol%), CCl4, reflux, 12 h, 80%; (e) i-PrMgBr (5 eq), CuI (0.1 eq), THF, HMPA, –5°C to 0 °C,

8 h, 45%; (f) BBr3 (5 eq), CH2Cl2, –78°C to 0 °C, 12 h, 91%; (g) 3,3-dimethylallyl bromide (1.2 eq),

K2CO3 (10 eq), acetone, reflux, 2 h, 90%; (h) urea (1.2 eq), 130 °C , 1 h, 81%; (i) NH2OH.HCl, pyridine,

reflux, 2 h, 76%.177

In the Argade synthesis (Scheme 2.02), natural products 31-34 were synthesised using a

chemo-selective SN2' Grignard coupling (step a, Scheme 2.02) and a chemo-selective

allylic substitution (step e, Scheme 2.02) as key reaction steps.177

This approach can be

used for derivatisation. However, the attachments at the C3 and C4 positions on the

heterocyclic core were each developed in three steps.177

Consequently, the Argade

31

synthesis was deemed unsuitable for our investigations. We envisioned the use of a

more efficient one step approach, developed within our group, to attach these

substituents for future derivatisation reactions (Scheme 2.03).

Scheme 2.03. Stewart synthesis of Antrodia camphorata natural products 31-33.166

Reagents and conditions: a) BnNH2, AcOH, 50°C, 16 h, 81%; (b) Pd2(dba)3.CHCl3 (10 mol %), PPh3 (20

mol %), i-BuZnBr, THF, 20°C, 18 h, 60%; (c) Pd2(dba)3 (10 mol %), P(t-Bu)3HBF4 (20 mol %),

Cy2NMe, dioxane, 20°C, 3 h, 76%; (d) KOH, THF/MeOH (1:2), 78 °C, 12 h then 2 M aq HCl, 20°C,

63%; (e) urea (1.2 eq), 130 °C , 1 h, 60%; (f) NH2OH.HCl, pyridine, reflux, 2 h, 79%.

The synthesis previously developed within our group is a convergent five-step synthesis

that uses two palladium catalysed cross-coupling protocols (the Negishi and Suzuki

reactions) as key steps (Scheme 2.03).166

This synthetic sequence appeared more suited

to our purposes because structural analogues could easily be prepared by simply altering

the Negishi and Suzuki cross-coupling partners to vary the alkyl and aryl fragments at

the C3 and C4 positions.

32

2.1.6 Aims of research

Our interest in the biological evaluation of Antrodia camphorata natural products and

their derivatives was largely inspired by the fungus's widely cited treatment for liver

cancer and the promising cytotoxic activity natural products 32 and 33 demonstrated

against Lewis lung carcinoma cell lines.1,2,137,176

Our first aim was to synthesise and evaluate the effects of the natural products 31-35 on

the proliferation of tumourigenic (PIL2) and non-tumourigenic (PIL4) liver progenitor

cells, in the hopes of finding an active lead. Our second aim was to obtain structure-

activity relationship (SAR) information through the synthesis and biological evaluation

of a number of maleic anhydride and maleimide derivatives. Ideally, a more potent lead

compound could be designed in the future, after a relationship had been established

between structure and pharmacological activity.

33

2.2 The Syntheses of Antrodia camphorata maleic anhydride and

maleimide natural products and their derivatives

As stated earlier, the chief aim of this project was to evaluate the effects of natural

products 31-35 and their structural derivatives on the proliferation of liver cells, in the

hopes of finding an anticancer lead. As a result, the main aim of our synthetic work was

to find reaction conditions that could be applied to the broadest range of substrates and

that gave us suitable quantities of compound for subsequent reactions and biological

evaluation. For this reason, many reactions with low to moderate yields were not

optimised. It was thought that the preparation of highly biologically active compounds

could be optimised individually, if required in larger quantities for future biological

investigations.

2.2.1 The synthesis of dichloromaleimide 46

3,4-Dichloromaleic anhydride 45 was the first precursor required for the total syntheses

of various maleic anhydride and maleimide natural products, and their derivatives. As

described earlier, maleic anhydrides and maleimides can be readily interconverted

(Scheme 2.01). Consequently, dichloromaleic anhydride 45 provides direct access to

both the maleic anhydride and maleimide core structures observed in the target

compounds. Additionally, the chlorine atoms on the heterocyclic backbone allow for

structural diversity to be introduced through palladium-catalysed cross-coupling

reactions at both the C3 and C4 positions.

Due to the ease with which maleic anhydrides undergo hydrolysis to the maleic acid

derivative, the first step in the synthetic pathway was to mask the maleic anhydride

functionality and convert it to the less reactive N-benzyl maleimide (Scheme 2.04).

Scheme 2.04. Reagents and conditions: a) BnNH2 (1.2 eq), AcOH, 55°C, 18 h, 81%.166,167

34

This was achieved via an acid-catalysed nucleophilic ring opening and subsequent

condensation of dichloromaleic anhydride 45 with N-benzyl amine. A standard

literature procedure for this transformation provided N-benzyl maleimide 46 as the sole

product in good yield (81%) (Scheme 2.04).72,166

2.2.2 The synthesis of isobutyl maleimide 48

After successfully completing the synthesis of dichloromaleimide 46, we proceeded to

introduce an isobutyl chain at the C4 position with a palladium-catalysed conjugate

substitution reaction via the Negishi protocol (Scheme 2.05).

Scheme 2.05. Reagents and conditions: a) Pd2(dba)3.CHCl3 (0.1 eq), PPh3 (0.2 eq), 47 (1.1 eq), THF,

20°C, 18 h, 60%.166

Palladium-catalysed conjugate substitution reactions refer to any palladium-mediated

reaction protocols such as the Negishi, Suzuki or Sonogashira reactions that occur

between an α,β-unsaturated carbonyl compound and an organic electrophile.50

The

reactivity order of halides in conjugate substitution reactions follows the same order as

for general palladium-mediated transformations that is, I > OTf > Br > Cl.50

However,

where chlorines are usually prone to slow and difficult oxidative addition, they undergo

oxidative addition with ease in β-halo-α,β-unsaturated carbonyl compounds due to the

electron deficient nature of the alkene. This was useful in this case because the

dichloromaleimide 46 is cheaper and accessible in fewer steps than its dibromo or

diiodo-maleimide counterparts.166,178

Thus, isobutyl maleimide 48 was obtained in a

reasonable yield (60%) using the optimised conditions previously developed within the

group (Scheme 2.05).166

35

2.2.3 The syntheses of boronic acid and ester Suzuki cross-coupling partners

As mentioned earlier, the Suzuki cross-coupling reaction was chosen to allow the

introduction of a variety of phenyl-substituents at the C3 position of the halogenated

isobutyl maleimide 48. We were especially interested in the effect on biological activity

of different para-substituents on the phenyl ring because natural products 33 and 35,

which differ only in their para-substituted phenyl rings, display different biological

activities. This indicated to us that the phenyl ring might be a key pharmacophore worth

investigating. As a result, we selected boronic acid and ester coupling partners based on

functional group modifications at this site. The specific modifications and reasons for

them will be discussed in more detail later on in this chapter.

In addition to purchasing many of the coupling partners selected for this medicinal

chemistry study, a number of boronic acids and esters were synthesised from a sequence

of lithium-halogen exchange reactions between the relevant aryl halides and n-BuLi,

followed by electrophilic trapping with triisopropyl borate 50 or dioxaborolane 51

(Scheme 2.06).85

Scheme 2.06. Reagents and conditions: a) i) n-BuLi (1 eq), THF, 50 (1.1 eq), -78°C, 1 h → rt, 2 h

ii) 1 M aq HCl; b) n-BuLi (1 eq), THF, 51 (1.1 eq), -78°C, 1 h → rt, 2 h.

Since the natural products contain a dimethylallyl ether at the para-position of the

aromatic ring, we were interested in derivatising this position with other lipophilic

ethers for SAR studies. Various alkyl aryl ethers were accessed via a Williamson

reaction between a number of primary alkyl bromides and para-bromophenol (52).72,179

36

Phenol 52 in acetone was treated under standard conditions with K2CO3, followed by a

suitable primary alkyl bromide. These conditions provided bromo alkyl aryl ethers 55,

57, 59, 61, and 63 in varying yields (Table 2.01).

Table 2.01. Williamson ether synthesis

Reagents and conditions: RBr (1.2 eq), K2CO3 (2 eq), acetone, reflux, 18 h.

Entry RBr Isolated Product† Isolated Yield

1

71

2

64

3

70

4

61

5

73

†The spectroscopic data for aryl ethers 55,

180-182 57,

182-184 and 63

185,186 matched that reported previously in

the literature.

The yields obtained for the ether reactions were moderate due to the poor solubility

of K2CO3 in acetone. Unfortunately, acetone could not be replaced with a solvent

such as water or an alcohol in which K2CO3 is more soluble because Williamson ether

syntheses involving phenols result in mixtures of oxygen-alkylated and carbon-

alkylated reaction products when conducted in polar-protic solvents

(Scheme 2.07).179,187

37

Scheme 2.07. Oxygen-alkylation versus carbon-alkylation, the effects of using a polar-protic solvent in

the Williamson reaction when the nucleophile is a phenoxide.187

Boronic acid synthesis:

With the required aryl bromides in hand, we proceeded to make the desired phenyl

boronic acids and esters. Lithium-bromine exchange between aryl bromides 55 and 57

(1 eq) and n-butyllithium (1 eq) in THF at -78°C, followed by electrophilic trapping

with triisopropyl borate 50, followed by an aqueous acidic workup gave the desired

boronic acids 65 and 66 in low yields of 22% and 43%, respectively (Table 2.02).188,189

The reactions were performed at -78°C to help minimise the formation of borane from

the borate by multiple nucleophilic displacements by the organolithium species.85

Table 2.02. Boronic acid synthesis

Reagents and conditions: i) n-BuLi (1 eq), THF, RBr (1.1 eq), -78°C, 1 h → rt, 2 h ii) 1 M aq HCl.

Entry RBr Isolated Product(s)† Isolated Yield(s)

1

43

2

22

† The spectroscopic data for boronic acids 65

190 and 66

191 matched that reported previously in the

literature.

A notable problem encountered with the described boronic acid products was their

purification. Boronic acids adhere well to polar stationary phases due to the Lewis

acidity of the boron atom, and because of the hydrogen-bond donor capabilities of the

two hydroxyl groups.85

It was found that when a crude mixture of the boronic acid was

38

subjected to column chromatography on silica gel, a significant proportion was not

recovered. Aside from adhering strongly to the silica gel, we were also concerned that

the boronic acids were undergoing acid-catalysed hydrolysis to boric acid 67

(equation1, Scheme 2.08).85,192-194

Additionally, recrystallisation was not pursued as a

purification process because of the tendency for boronic acids to dehydrate to their

anhydrides in non-polar solvents (equation 2, Scheme 2.08).85

Scheme 2.08. 1) Acid-catalysed hydrolysis of boronic acid to boric acid; 2) dehydration of boronic acid

to an anhydride.85

Boronic ester synthesis:

In order to avoid the aforementioned purification difficulties we focussed on the

synthesis of less polar cyclic boronic esters that are traditionally easier to isolate and

purify.85,195

Lithium-bromine exchange between various aryl bromides and

n-butyllithium in THF at -78°C, followed by electrophilic trapping with dioxaborolane

51, workup, and then subsequent purification by column chromatography on silica gel

gave the desired boronic esters 71-76 in varying yields (Table 2.03).

39

Table 2.03. Boronic ester synthesis

Reagents and conditions: i) n-BuLi (1.1 eq), THF, RBr (1 eq), -78°C, 1 h → rt, 2 h.

Entry R Yield Entry R Yield

1

79% 4

93%

2

66% 5

73%

3

89% 6

85%

†The spectroscopic data for the boronic esters 71,

196 72,

197,198 73,

199,200and 76

185 matched that reported

previously in the literature. Boronic esters 72, 74, and 76 were also purchased commercially.

As can be observed from Table 2.03, the yields after purification on silica gel were

much higher for the boronic ester derivatives than for the boronic acid derivatives. The

less polar boronic esters were not retained on the silica gel and eluted from the columns

quickly and easily. The only exception was the toluene derivative 72, which had a

significantly lower yield in comparison to the other boronic esters.

In general, boronic acids and esters react as mild Lewis acids because of boron’s

deficient valence.85

As would be expected, electron-withdrawing substituents on the

boron atom increase its Lewis acid strength and electron-donating groups decrease its

acid strength.201-204

For aryl groups on the boron atom, the relative order of Lewis

acidity for the different types of boronic esters is aryl > para-aryloxy.85

This is because

para-donating groups increase the electron density around the boron atom and make it

less electrophilic, and less susceptible to nucleophilic attack. As a result of this, we

suspected that the toluene derivative was more susceptible to hydrolysis than its para-

aryloxy counterparts.

With the exception of the aryl pentyl ether 75 the boronic esters 71-76 were obtained

commercially or previously synthesised in the literature. The key spectroscopic features

40

for 75 were as follows: the molecular formula C17H27BO3 was determined by HRMS

(calc. for C17H28BO3 [M + H]+ 291.2131, found 291.2132); the

1H NMR spectrum

indicated a resonance at δ = 1.35 (12H) which was assigned to the four methyl groups.

Not surprisingly, only three aromatic carbons were observed in the 13

C NMR at

δ = 113.99 (ArCH), 136.61 (ArCH), and 161.89 (ArC). This observation is consistent

for aromatic carbons of boronic esters where the quaternary carbon next to the 11

B atom

is broadened beyond detection limits. The IR spectrum showed a strong band attributed

to a B–O stretch at 1361 cm–1

.

2.2.4 The syntheses of maleimide derivatives via the Suzuki reaction

With the required boronic acids and esters in hand, it was the stage of the synthesis to

introduce a variety of phenyl substituents to the C3 position of isobutyl maleimide 48

via the Suzuki protocol. Encouraged by earlier success within the group, we applied the

catalytic conditions developed by Fu et al.90

to the reaction between chloromaleimide

48 and a number of boronic esters. After observing a number of moderate yields with

these conditions, we suspected that this catalytic system was not optimal for our range

of substrates and so a variety of conditions varying the catalyst, base, solvent, and

substrate were trialled (Table 2.04).

41

Table 2.04. Optimisation conditions for the Suzuki cross-coupling reaction

Reagents and conditions: catalyst (10 mol%), ligand (20 mol%), base (2 eq), reflux, 18 h.

Entry R Catalyst Base Solvent Yield

1

Pd2(dba)3/

P(t-Bu)3HBF4

55%

2

PdCl2(dppf) NaOH THF 91%

3

PdCl2(dppf) NEt3 THF 0%

4

Pd2(dba)3/

P(t-Bu)3HBF4

27%

5


6

Pd(PPh3)4 NaOH THF 0%

7

PdCl2(dppf) K2CO3 DME 0%

8


9

Pd2(dba)3.CHCl3/

P(t-Bu)3HBF4

44%

10

Pd2(dba)3.CHCl3/

PPh3 Na2CO3 THF 14%

It appeared that the reaction conditions using an amine or non-oxy base (entries 1, 3, 4,

7, 9 and 10, Table 2.04) were less successful in producing the desired product than

42

conditions using an oxy base (entries 2, 5, and 8, Table 2.04). The reaction conditions

comprising of PdCl2(dppf), with NaOH and THF (entries 2, 5, and 8, Table 2.04)

appeared to give the highest yields of product (entries 2, 5 and 8, Table 2.04). As

discussed in the introduction, these are standard Suzuki cross-coupling reaction

conditions that work for a wide range of substrates. Thus, these were the reactions

conditions employed to attach various aryl fragments to the C3 position of the

maleimide core. Subjecting the chloro maleimide 48 to Suzuki cross-coupling reactions

with various boronic acids and esters provided a number of aryl maleimides in various

yields (Table 2.05).

Table 2.05. Suzuki reaction

Reagents and conditions: PdCl2(dppf) (10 mol%), NaOH (3 eq), THF, reflux, 18 h.


1

90% 8

17%

2

91% 9

63%

3

60% 10

32%

4

16% 11

58%

5

74% 12

48%

6

12% 13

84%

7

63% 14

0%

43

The conditions described earlier afforded all the desired products except the pyridine

derivative in yields suitable to proceed with in the next few steps.

To verify the structures of the many new N-benzyl maleimides that were synthesised, a

number of key spectroscopic features were identified (these can be found in the

experimental section). In all cases the molecular formulas were assigned by HRMS, the

IR spectra showed characteristic stretches in the carbonyl group region, and the 1H

NMR, 13

C NMR and DEPT spectra showed signals that could be assigned to key

structural moieties in the molecules. The appearance of resonance signals in the NMR

spectra that corresponded to the addition of new para-substituted aromatic side chains

were the key spectroscopic features that indicated that the Suzuki reactions were

successful.

Natural products 34 and 35, also isolated from Antrodia camphorata, contain a phenol

group. Synthesis of the phenol side chain for these targets was approached in two

different ways. The first method involved a coupling reaction between isobutyl

maleimide 48 and a phenol boronic acid. This method gave phenol 85 in 60% yield. The

second method involved starting with the coupled product 78 and then cleaving the

isopropoxy group with the Lewis acid AlCl3 to give phenol 85 via the conditions

developed by Banwell et al.205

(Scheme 2.09). The latter set of conditions provided

phenol 85 in a higher yield of 80%.

Scheme 2.09. Reagents and conditions: a) i) AlCl3 (1.3 mmol), CH2Cl2, rt, 3 h; ii) 37% w/w aq NH4Cl,

80%.205

Phenol 85 provided us with an alternative key intermediate to synthesise various aryl

ether derivatives. Conducting Williamson ether reactions with phenol 85 and various

alkyl halides would be a more cost-effective and efficient way to access various alkyl

ethers because it eliminates the need to synthesise various bromo aryl ethers and their

44

corresponding boronic esters. If the reaction steps for the synthesis of phenol 85 could

be optimised, this would be a more feasible key intermediate for the synthesis of future

aryl ether maleic anhydride and maleimide derivatives.

2.2.5 The syntheses of maleic anhydride derivatives

With structurally diverse N-benzyl maleimides 78-93 in hand, we could access our

target maleic anhydride derivatives. Using the same conditions employed by

Stewart et al.166

a number of maleic anhydrides were synthesised by heating the

required N-benzyl maleimide with an excess of KOH (6 eq) in a mixture of methanol,

THF, and water (1:2:2) at reflux. It was assumed that alkaline saponification of the

maleimide forms a diacetate or maleic acid intermediate, which then undergoes

dehydration with concomitant ring-closure to give a maleic anhydride. One of the

driving forces for ring-closure appears to be the relief of non-bonded interaction strain

in the acyclic molecule, which can be effectively relieved in the cyclic anhydride

form.174

This is a result of the relief in R1-R2 steric strain interactions because of the

larger R1-C=C-R2 angle in the maleic anhydride (128.5°) as compared to the analogous

maleic acid (118°) in combination with the fact that the COOH-COOH interactions in

the maleic acid disappear upon ring closure (Scheme 2.10).174,206

Scheme 2.10. The relief of non-bonded interaction strain.

The conditions described provided maleic anhydrides 97-107 in varying yields

(Table 2.06).

45

Table 2.06. Maleic anhydride synthesis

Reagents and conditions: KOH (6 eq), THF/H2O/MeOH (2:2:1), reflux, 18 h.


1

73% 7

90%

2

48% 8

58%

3

94% 9

68%

4

79% 10

0%

5

31% 11

0%

6

63% 12

73%

A major problem encountered with many of the maleic anhydride products was their

purification. For some maleic anhydrides, it was found that when a crude mixture of the

anhydride was subjected to column chromatography on silica gel, a significant

proportion was hydrolysed to the analogous maleic acid (Scheme 2.10). In their maleic

acid forms, the compounds interacted strongly with the silica gel and could not be

eluted. Column chromatography performed with basic alumina or silica gel deactivated

with NEt3 did not make any significant differences to the isolated yields.

The position of equilibrium between a maleic acid and its maleic anhydride derivative

relies mainly on two things: 1) the relief of non-bonded interactions, as described

previously; and 2) entropic facrors. Substituent group electronics affect the reactivity of

the carbonyl group.207,208

Electron-withdrawing substituents at R1 or R2 increase the

+δ character of the acyl carbon and make it more susceptible to nucleophilic

46

attack.174,206-208

For compounds with strong electron-withdrawing groups, equilibrium

favours the acyclic compound, because these molecules are prone to nucleophilic ring-

opening reactions, and vice versa.207,208

In regards to the compounds in Table 2.06, compounds 99 (entry 3) and 103 (entry 7)

showed the highest reaction yields of 94% and 90% respectively. Understandably, these

compounds would favour the anhydride because, by virtue of conjugation, the strong

para-donating groups (NH2 and OH) on the phenyl ring increase the electron density

around the acyl carbon, and make it less prone to nucleophilic ring opening. However,

less understandable is why this trend was not observed for all the aromatic side chains

containing para-donating groups such, as compounds 98, 101, 104, and 105 (Entries 2,

5, 8 and 9). The conditions above were also repeated on an N-benzyl maleimide with an

electron-withdrawing aromatic substituent at the para-position of the phenyl ring (entry

11). Unfortunately, this product could not be isolated. We suspected that the compound

was lost in the aqueous layer or retained on the column as its maleic acid derivative.

The structures of the various maleic anhydrides were verified in much the same way as

for the N-benzyl maleimides. That is, by identifying a number of key spectroscopic

features (these can be found in the experimental section): in all cases, the molecular

formulas were assigned with the aid of HRMS; the 1H NMR,

13C NMR and DEPT

spectra showed signals that could be assigned to key structural moieties. The distinct

lack of signals in the NMR spectra that could be attributed to benzyl moieties indicated

the successful removal of the benzyl protecting groups; the IR spectra showed sharp

peaks for the imide carbonyls and no broad peaks in the OH region, which indicated

that the compounds synthesised were the maleic anhydrides and not the maleic acid

derivatives.

2.2.6 The syntheses of maleimide derivatives

Finally, with maleic anhydrides 97-107 in hand, we could access our target maleimide

derivatives using existing methodology. Using the conditions developed by

Ficken et al.209

various N-H maleimides were synthesised by heating urea with the

required maleic anhydride at 140°C for 4 hours (Table 2.07). Urea decomposes to

ammonia and other by-products at temperatures above its melting point of 133°C.210

It

was assumed that the released ammonia and the anhydride underwent a nucleophilic

47

ring-opening reaction, which was followed by ring closure via a condensation reaction

to produce the desired N-H maleimides (see Scheme 2.01 for the proposed

mechanism).157

Table 2.07. Maleimide synthesis

Reagents and conditions: Urea (5 eq), 140°C, 2 h.


1

67% 8

50%

2

43% 9

52%

3

72% 10

40%

4

60% 11

46%

As can be observed in Table 2.07, these conditions provided the desired maleimides,

but only in moderate yields. A possible explanation for this could be the occurrence of

competing side reactions. At elevated temperatures, urea can react with anhydrides to

form nitriles211

or with α,β-unsaturated carbonyl compounds to form a variety of

nitrogen heterocycles212

(Scheme 2.11). The maleimides were the major products

isolated from the reactions mixtures, but TLC analysis showed that they were not the

only products present. Unfortunately, no other products were isolated or characterised to

get a better mechanistic understanding of what types of side reactions might be

occurring.

48

Scheme 2.11. The reaction between urea and anhydrides or urea and α,β-unsaturated carbonyl compounds

can form nitriles or a variety of nitrogen heterocycles at elevated temperatures.211

212

As discussed earlier, reactions yields were not the deciding factor when determining

appropriate reaction conditions. Urea was chosen as an ammonia source because it was

more convenient to use, and easier to handle than liquid ammonia. These reasons made

the conditions described above the most desirable choice for the synthesis of a large

number of derivatives. Unfortunately, one anhydride (aniline 103) decomposed when

exposed to these conditions and the analogous N-H maleimide could not be accessed.

For the most part, however, these reaction conditions provided adequate amounts of the

desired maleimides for characterisation and biological evaluation.

The structures of the various maleimides 109-116 were verified by identifying a number

of key spectroscopic features (these can be found in the experimental section): in all

cases, the molecular formulas were assigned by HRMS; the 1H NMR,

13C NMR and

DEPT spectra showed signals that could be assigned to new and key structural moieties

such as the imide hydrogens (N-H); the IR spectra showed broad N-H peaks and sharp

peaks for the imide carbonyls. The appearance of peaks for the N-H group in the 1H

NMR and IR spectra were the key spectroscopic features that indicated the successful

synthesis of N-H maleimides 109-116 from maleic anhydrides 97-102, 104, and 105.

Maleic anhydride 34 was treated with NH2OH.HCl and pyridine at 100°C for 12 hours

to give maleimide 35 in 72% yield (Scheme 2.12). Natural product 35 had not been

previously synthesised. The spectroscopic data for maleimide 35 matched that reported

previously in the literature.2

49

Scheme 2.12. Reagents and conditions: a) NH2OH.HCl (eq), pyridine, 100°C, 12 h, 72%.

Most routes to N-H maleimides from N-protected maleimides involve two steps: the

synthesis of a maleic anhydride from a protected maleimide, followed by reintroduction

of nitrogen to synthesise a free maleimide. For our current studies, this was perfectly

satisfactory because we needed to access maleic anhydride and N-H maleimide

derivatives. However, in the future, it would also be convenient if a N-H maleimide

could be accessed directly in one step from a N-protected maleimide. A study conducted

by Watson et al.213

revealed that the 2,4-dimethoxybenzyl group (highlighted in red)

can be used to protect maleimide nitrogens and be cleaved to a N-H maleimide in one

step using TFA and anisole (Scheme 2.13). This is a protecting group strategy that we

intend to investigate further in the future.

Scheme 2.13. Reagents and conditions: a) TFA (50 eq), anisole (50 eq), 90°C.213

50

51

2.3 The Biological evaluation of Antrodia camphorata maleic

anhydride and maleimide natural products and their derivatives

As stated earlier, the natural products 31-35 were isolated from an extract of the

mycelium of Antrodia camphorata.1 This extract, containing a mixture of compounds,

has widely been cited as a treatment for liver cancer and has more recently been shown

to decrease cell growth and induce apoptosis in two human liver cancer cell lines.137

Despite this, the natural products 31-35 had not been tested directly against

tumourigenic liver cell lines to determine if they showed any promising biological

activity individually.

The purpose of our biological investigations was to evaluate the effects of natural

products 31-35 on the proliferation of tumourigenic (PIL2) and non-tumourigenic

(PIL4) liver progenitor cells and then to obtain structure-activity relationship (SAR)

information through the synthesis and biological evaluation of a number of maleic

anhydride and maleimide derivatives. The biological effects of the maleic anhydride and

maleimide natural products and their derivatives was determined experimentally by

using the Innovatis Cellscreen systemTM

to monitor and quantify cell growth over time.3

The Cellscreen system is an non-invasive automated technique that reliably detects a

decrease or increase in cell proliferation and quantifies this change by providing cell

doubling times for test cultures.3 Unlike traditional methods that involve arduous

cell counting techniques and require cells to be sacrificed at each time point to measure

cell growth, the Cellscreen system leaves cells unaltered and intact. As a result

of this, it is possible to continuously measure the growth of the same culture of cells.

The Cellscreen system consists of a microscopy unit that collects digital images

of the cells cultured in microtitre wells. Special pattern-recognition software then

determines the cell density by measuring the area that is occupied by adherent cells

(image b, Figure 2.05). The software then quantifies the cell density as a

percentage that can then be used to plot a growth curve of cell density (%) versus time

(image c, Figure 2.05). This curve can then be manipulated to calculate the doubling

time in hours for the cell culture.3

52

0

10

20

30

40

50

60

70

0 5 22 30 57 80

Ce

ll D

en

sity

(%)

Time (h)

PIL4

PIL2

(a) (b) (c)

Figure 2.05. a) Image of PIL4 adherent cells; b) measurement of cell density with the Cellscreen system,

the images in red outline cells, whereas regions marked in blue are considered to be spaces or uncovered

well areas that are subtracted; c) a typical growth curve for PIL2 tumourigenic and PIL4 non-

tumourigenic cell lines.3

For our assays, PIL4 and PIL2 cells in supplemented William's E medium (Sigma

Aldrich) were seeded in 96-well microtitre plates. Once the cells had attached and

reached 5-10% of the well area, the test compounds were added and the growth was

monitored twice daily over the next four days. Growth of the cells containing test

compounds in DMSO (6 repeats per compound) were compared with growth of the

control cells containing no test compounds and DMSO. The cell doubling time can vary

depending on the initial density of the plating; this is why doubling times vary between

control experiments. For all experiments, the cell densities going across a row are

equivalent but might vary between rows. As a result of this, growth of the cells

containing test compounds were always compared against growth of the control cells in

the same row.

2.3.1 Biological assay results for natural products 31-35 against PIL2 and PIL4

cell lines

Using the cell proliferation assay described previously, the cell doubling times for PIL2

and PIL4 cell lines exposed to natural products 31-35 at concentrations of 10 μM,

50 μM, and 100 μM are shown below in Table 2.09.

53

Table 2.09. The effect of natural products 31–35 on cell doubling time (CDT) in PIL2

(tumourigenic) and PIL4 (non-tumourigenic) cell lines

Cell Doubling Time (h)

Entry Compound Cell linea Control

b 10 μM

c 50 μM

c 100 μM

c

1 31 PIL4 25 h 25 h 27 h 50 h

2 31 PIL2 40 h 52 h 44 h 38 h

3 32 PIL4 25 h 26 h 30 h #

4 32 PIL2 20 h 21 h 33 h #

5 33 PIL4 25 h 25 h 27 h 35 h

6 33 PIL2 40 h 13 h 10 h 11 h

7 34 PIL4 28 h 29 h 32 h 31 h

8 34 PIL2 27 h 27 h 28 h 26 h

9 35 PIL4 35 h 35 h 36 h 31 h

10 35 PIL2 27 h 27 h 30 h 32 h

a) Immortalised liver cell lines: PIL4 (non-tumourigenic) and PIL2 (tumourigenic); b) for each control

experiment, the doubling time varies slightly depending on the initial density of plating, with higher

density cultures showing longer doubling times; c) cell doubling time for the compound concentration "#"

indicates that the cell line has not undergone doubling in 108 h, and that the indicated compound was

highly effective in cell proliferation arrest.

It was observed that maleic anhydride 31 failed to have an influence on cell growth in

the PIL4 non-tumourigenic model at 10 μM and 50 μM concentrations (Table 2.09,

entry 1). However, once the concentration of compound 31 was increased to 100 μM, a

significant inhibition of cell growth was observed; this can be seen from the increase of

the cell doubling time by a factor of 2 (Table 2.09, entry 1). Surprisingly, also for

maleic anhydride 31 lower concentrations of compound 31 (10 μM and 50 μM)

appeared to be more effective in inhibiting cell growth in the tumourigenic cell line than

a higher concentration of 100 μM (Table 2.09, entry 2). In the case of the natural

product maleimide 32, cell proliferation was dramatically inhibited at 100 μM

concentrations, but with no preference for either cell line (Table 2.09, entries 3 and 4).

The N-OH maleimide 33 did not appear to have any significant effect on the doubling

time of the PIL4 cell line (Table 2.09, entry 5), but appeared to hasten the doubling

time of the tumourigenic PIL2 cell line at all the concentrations tested (Table 2.09,

entry 6). The remaining natural products 34, and 35 did not appear to have any

significant influence on the doubling time of the PIL2 or PIL4 cell lines (Table 2.09,

entries 7-10).

54

The natural products 31 and 32 seemed to be the most effective at slowing cell

proliferation in both the cell lines and thus were chosen as scaffolds for further

structural modification (as described in the synthesis section of this chapter).

Interestingly, maleimide 32 was also the most potent of the five natural products

(31-35) when tested against Lewis lung carcinoma cell lines in the initial biological

assays conducted by Nakamura et al.1

2.3.2 Biological assay results for maleic anhydride derivatives 97-105 against

PIL2 and PIL4 cell lines

For our SAR study, the core heterocyclic ring was restricted to maleimides and maleic

anhydrides because of the initial promising biological activities of compounds 31 and

32. Furthermore, since the isobutyl fragment is common to natural products 31–35, and

all display varying cell-proliferation inhibitory properties, we decided that the aryl

group substitent might play a key role in biological activity and thus initially

investigated only different para-substituted aryl derivatives for structure-activity

relationship information (SAR). It was decided that selecting and introducing different

alkyl side chains for SAR information would be a future goal.

In this initial SAR study, general physical and chemical changes were made to the para-

substituent on the phenyl ring: the length and the steric properties of the alkyl side chain

were altered (97, 98, 100, 102, 105, 106, 109, 110, 112, 114, and 116); the alkyl side

chain was changed from unsaturated to saturated (101 and 103); the lipophilicity of the

side chain was increased by removing the ether oxygen (97, 100, 102, 106, 109, 112,

and 114); and hydrogen bond donor/acceptor sites were introduced (99, 103, 104, 111,

and 115). Unfortunately, derivatives containing electron-withdrawing groups on the

phenyl ring could not be synthesised for biological evaluation.

Using the cell proliferation assay described previously, the cell doubling times for PIL2

and PIL4 cell lines exposed to maleic anhydride derivatives 97-107 at concentrations of

10 μM, 50 μM, and 100 μM are shown below in Table 2.10.

55

Table 2.10. The effect of maleic anhydrides 97–105 on cell doubling time in PIL2 and

PIL4 cell lines


Entry Compound Cell line Control 10 μM 50 μM 100 μM

1

PIL4 24 h 29 h 34 h 29 h

2

PIL2 17 h 20 h 17 h 17 h

3

PIL4 23 h 23 h 27 h 26 h

4

PIL2 25 h 24 h 23 h 23 h

5

PIL4 23 h 23 h 27 h *

6

PIL2 25 h 26 h 37 h *

7

PIL4 23 h 25 h 27 h 26 h

8

PIL2 24 h 23 h 25 h 27 h

9

PIL4 25 h 29 h * *

10

PIL2 23 h 30 h * *

11

PIL4 22 h 30 h 32 h 37 h

12

PIL2 25 h 36 h 49 h 55 h

13

PIL4 23 h 22 h 24 h 27 h

56

Table 2.10. The effect of maleic anhydrides 97–105 on cell doubling time in PIL2 and

PIL4 cell lines (continued ...)


Entry Compound Cell line Control 10 μM 50 μM 100 μM

14

PIL2 26 h 27 h 27 h 36 h

15

PIL4 17 h 20 h 24 h 23 h

16

PIL2 18 h 21 h 22 h 2 h



density cultures showing longer doubling times; c) cell doubling time for the compound concentration "*"

indicates that the compound crystallised out in the cell assay leading to an ineffective reading in the

Cellscreen recognition software.

Maleic anhydride derivative 97 containing no substituents on the phenyl ring did not

appear to have any significant effect on cell proliferation for either PIL4 or PIL2 cell

lines at any concentration (Table 2.10, entries 1 and 2). This suggested that a

substituent on the phenyl ring is necessary for activity. Maleic anhydride derivative 100

which contains an isobutyl side chain at the para-position of the phenyl ring, but with

no oxygen, also failed to show any significant effect on cell proliferation for either cell

line (entries 5 and 6).

Maleic anhydride derivative 102, also lacking an oxygen at the para-position, but

containing a n-butyl group as a side chain, showed selective activity at a concentration

of 50 μM against the tumourigenic PIL2 cell line, while remaining relatively ineffective

in the PIL4 non-tumourigenic cell line (entries 9 and 10). The straight aliphatic chain

could play a role in effecting cell growth, possibly through a hydrophobic binding

pocket. Additionally, the activity of this derivative also suggests that the oxygen of the

aryl fragment is not necessary for activity. Unfortunately, it was impossible to

determine if this trend continued with an increasing concentration because the

compound crystallised out of solution at higher concentrations. This meant no

discernable or reliable result could be obtained for the higher concentrations (50 μM,

100 μM) from the Cellscreen software.

57

The isopropyl aryl ether derivative 98, with a shorter more saturated alkyl ether tether

relative to the natural product, failed to show any change to cell proliferation in either

cell line (entries 3 and 4). Compound 101 which is analogous to natural product 31,

except that the alkyl chain is saturated, appeared to increase cell growth inhibition at

10 μM (entries 7 and 8). Unfortunately at 50 μM and 100 μM concentrations the

compound crystallised out of solution, and again no discernable results could be

obtained (entries 7 and 8).

The aniline derivative 103 was especially interesting. While it inhibited cell growth in

both the PIL4 and PIL2 cell lines, it was considerably more active in the tumourigenic

PIL2 line (entries 11 and 12). In terms of the molecular mode of action, the aniline

could be a potential hydrogen bond donor and acceptor group. While the aniline

derivative 103 showed considerable activity, the dimethyl aniline 104, did not show any

dramatic effects on cell proliferation (entries 13 and 14). This suggested that perhaps

aniline 103 is interacting at a functional site through hydrogen bonding. Derivative 105

with a bulky benzyl ether side chain did not shown any significant activity at any

concentration in either the PIL4 or PIL2 cell lines (entries 15 and 16).

2.3.3 Biological assay results for maleimides 109-116 against PIL2 and PIL4 cell

lines

The corresponding maleimides were also assayed using the previously described cell

proliferation assay. The cell doubling times for PIL2 and PIL4 cell lines exposed to

maleimide derivatives 109-116 at concentrations of 10 μM, 50 μM, and 100 μM are

shown below in Table 2.11.

58

Table 2.11. The effect of maleimides 109–116 on cell doubling time in PIL2 and PIL4

cell lines



b 10 μM

c 50 μM

c 100 μM

c

1

PIL4 21 h 22 h 22 h 25 h

2

PIL2 19 h 19 h 20 h 23 h

3

PIL4 28 h 28 h # #

4

PIL2 27 h 28 h # #

5

PIL4 35 h 35 h # #

6

PIL2 27 h 28 h # #

7

PIL4 23 h * * *

8

PIL2 24 h * * *

9

PIL4 25 h 30 h 31 h 47 h

10

PIL2 23 h 28 h 27 h 30 h

11

PIL4 21 h 19 h 35 h 90 h

12

PIL2 19 h 20 h 29 h 80 h

59

Table 2.11. The effect of maleimides 109–116 on cell doubling time in PIL2 and PIL4

cell lines (continued ...)



b 10 μM

c 50 μM

c 100 μM

c

13

PIL4 16 h 22 h 20 h 34 h

14

PIL2 17 h 20 h 21 h 48 h



density cultures showing longer doubling times; c) cell doubling time for the compound concentration "*"

indicates that the compound crystallised out in the cell assay leading to an ineffective reading in the

Cellscreen recognition software, concentration "#" indicates that the cell line has not undergone doubling

in 108 h, and that the indicated compound was highly effective in cell proliferation arrest.

The derivative 109 containing no substituents on the phenyl ring did not appear to have

any significant effect on cell proliferation in the maleimide form either (entries 1 and 2,

Table 2.11). The isobutyl derivative 112 that failed to show any significant activity in

the maleic anhydride form, showed phenomenal activity in the maleimide form: the cell

population did not double during a 108 hour period for either PIL4 or PIL2 cell lines

(entries 5 and 6).

The butyl derivative 114 showed activity (entries 10 and 11). However, 114 did not

show selective activity in the tumourigenic cell lines, unlike the maleic anhydride butyl

derivative 102. Instead it appeared to significantly arrest cell growth in both the PIL2

and PIL4 cell lines, the doubling time exceeding the 108 hour period of the experiment.

Structurally speaking, the alkyl side chain could again be interacting with a hydrophobic

binding pocket.

There were no discernable results for the maleimide 110 containing the isopropyl aryl

ether substituent, because the compound crystallised out of solution (entries 3 and 4).

Isopentyl aryl ether 113 showed a slight increase in the cell doubling time as the

concentration increased for the PIL2 cell line, but showed a more significant increase in

cell doubling time for the PIL4 cell line (entries 7 and 8). The dimethyl aniline

derivative 115 showed a dramatic increase in doubling time for both cell lines when the

60

concentration was increased to 100 μM (entries 11 and 12). Derivative 116 with a bulky

benzyl ether side chain did not shown any significant activity at 10 μM or 50 μM

concentrations, but did considerably slow cell proliferation at 100 μM in both the PIL4

and PIL2 cell lines (entries 13 and 14).

2.3.4 Overview of biological assay results

A number of maleic anhydride and maleimide derivatives (102, 103, and 112-116)

appeared to hinder cell proliferation in both the PIL4 and PIL2 cell lines at a variety of

concentrations, but the majority of the compounds were unselective in doing so (112-

116). In terms of structure-activity relationships trends, it was difficult to determine

specific trends because there were great structural differences between many of the

active compounds. It is possible that the different compounds target different active

sites or have varying membrane permeablities. It appeared that the aryl butyl derivatives

102 and 114, were the most active compounds because they significantly hindered cell

growth in both PIL2 and PIL4 cell lines. This increased activity, relative to the natural

products, could indicate that these compounds interact with a hydrophobic binding site.

Judging from the results it would also appear that the oxygen atom of the aryl ether

fragment is not necessary for activity.

Most interestingly, two compounds (102 and 103) showed selective and increased

activity in the tumourigenic PIL2 cell line. In both cases these compounds were maleic

anhydrides, however the substituent on their aromatic fragments were very different.

Without knowing the mode of action of these compounds, their membrane

permeablities, or the active sites they target, it is impossible to say why these

compounds showed selectivity. However, as described earlier, maleic anhydrides in

solution exist in equilibrium with their maleic acid or acetate form. Perhaps this ability

to form a charged species in situ contributes to their selectivity in tumourigenic cell

lines. Unfortunately, the maleimide of the aniline derivative could not be prepared to

give us more of a mechanistic insight on whether it is the anhydride moiety or the aryl

substituents that are most affecting the selectivity.

Ideally in the future, further investigations will be done to elucidate the molecular

modes of action, cellular modes of action, and membrane permeablities for the active

compounds. Tailored structural modifications could then be made to the compounds

61

based on the chemical and physical nature of the active site, which would better help to

optimise their biological activity.

2.4 Syntheses, spectroscopy, and quantum chemical calculations of

fluorescent maleimide derivatives

Fluorescent molecules have found many applications in chemical and biological

research. An area of particular interest is the use of fluorescent molecules as probes,

where a thorough knowledge of the excitation and absorption properties of fluorescent

molecules means that they can be used in microscopy and spectroscopy to isolate the

location of organelles or proteins, for fluorometric detection in HPLC, to detect

electrical or chemical changes in the environment, or to determine protein

interactions.214-221

Ideally, there would be an accurate method to predict the fluorescent properties of a

molecule from its chemical structure so that molecules with the desired fluorescent

properties could be synthesised more efficiently. It had not been clear how accurately

the fluorescent properties of molecules could be predicted from theoretical calculations

such as the Hartree-Fock configuration interaction (singles) theory (HF-CIS), time

dependant density functional theory (TDDFT), or the semi-empirical AAM1/ZINDO

approach.222-237

Thus, the purpose of our studies was to synthesise a number of new

fluorescent bis-maleimides so that our collaborators in theoretical chemistry could use

these compounds, in conjunction with some previously synthesised fluorescent

compounds, to compare computational absorption and emission data against

experimental data, in order to determine the accuracy of the previously described

methods in determining fluorescent properties.

Using the Suzuki conditions employed previously, the reaction between

dichloromaleimide 46 and various boronic esters and acids in the presence of

PdCl2(dppf) and NaOH in THF gave bis-aryl maleimides 124-129 in varying yields

(Table 2.12).

62

Table 2.12. Suzuki reaction

Reagents and conditions: PdCl2(dppf) (10 mol%), NaOH (3 eq), THF, reflux, 18 h.


1

30% 4

9%

2

6% 5

45%

3

46% 6

18%

The experimental fluorescence data of these compounds and a number of other known

maleimides was compared with predicted data.238

Calculated absorption and emission

wavelengths using semi-empirical AAM1 with excited state ZINDO calculations

showed that predicted wavelengths were within an average deviation of less than 6% for

absorption maxima and less than 4% for emissions peaks. This indicates that the semi-

empirical AAM1/ZINDO approach is accurate enough to be used for future theoretical

predictions of fluorescence spectra. This discovery has many potential applications in

research and industry (as discussed earlier) because it means that fluorescent molecules

can be designed, and then synthesised, to expedite the process of obtaining molecules

with desired fluorescence properties.

63

2.5 Conclusions and future work

In conclusion, a number of maleic anhydride and maleimide natural products (31-35)

and their derivatives (97-107, and 109-116) were synthesised using the Negishi and

Suzuki cross-coupling protocols as key reaction steps. Several synthesised natural

products and their derivatives (102, 103, 112-116) were shown to be potent in slowing

cell growth when evaluated for biological activity against both tumourigenic and non-

tumourigenic p53 immortalised liver cell lines. Especially significant were compounds

102 and 103 which showed increased slowing of cell proliferation in the tumourigenic

cell lines compared to the non-tumourigenic cell lines. Unfortunately, we could not

establish any clear relationships between structure and pharmacological activity because

there were great structural differences between many of the active compounds. In the

future, for the active compounds, we hope to use the fluorescent properties of the

molecules to help identify the cellular targets responsible for the biological activities

observed. In addition, we plan to test the compounds against a host of other cancer cell

lines, including breast cancer cell lines, for biological activity.

The synthetic sequence established by our research group was also applied to access a

number of bis-substituted maleimide derivatives. These fluorescent molecules were then

tested alongside a number of other fluorescent molecules to show that theoretical

calculations using the semi-empirical AAM1/ZINDO approach can be used to predict

fluorescent wavelengths with reasonable accuracy (less than 6% for absorption maxima

and less than 4% for emissions peaks).

64

65

Chapter 3

Studies into the Total and Formal Syntheses of SDEF 678 and

Speciosins A-F

66

67

3.1 Introduction

3.1.1 Cyclohexenone epoxide natural products

The cyclohexenone epoxide* family of compounds containing the 7-oxabi

cyclo[4.1.0]hept-3-en-2-one structural moiety (highlighted in red, Figure 3.01) displays

a diverse range of complex molecular structures. These compounds are produced by

microorganisms isolated from various plants and animals which show a variety of

antibacterial, antifungal, antitumor, enzyme inhibitory, and antimitotic biological

activities.4,5,239,245,247-257

Some interesting examples of cyclohexenone epoxide natural

products are presented below to highlight the structural diversity found within this

structural class (Figure 3.01).

Figure 3.01. A variety of cyclohexenone epoxide natural products: epoformin (130);252,253

harveynone

(131);254

terreic acid (132);245

tricholomenyn A (133);248

flagranone C (134);247

enaminomycin B (135);255

(+)-UCF76 B (136);256

and (+)-ambuic acid (137).257

* In this text, the term cyclohexenone epoxide is used specifically to refer to compounds containing the 7-

oxabicyclo[4.1.0]hept-3-en-2-one structural moiety. However, in the literature, the term actually

encompasses a wider range of compounds not limited to the core structure highlighted.239-249

68

Cyclohexenone epoxides are highly functionalised, mostly with oxygen, and they often

contain a number of contiguous chiral stereogenic carbon centres on the key ring

system (Figure 3.01). The nature of the substituents on the ring can vary significantly in

their number, complexity, stereochemistry, and functionality.

Most cyclohexenone epoxides containing the 7-oxabicyclo[4.1.0]hept-3-en-2-one

structural moiety show antimicrobial activity and are generally produced as secondary

metabolites of fungi that provide protection to their host organisms against pathogenic

microbes.4,239,249,258

Despite this common trait, no clear picture for their mode of action

has emerged so far. Given the highly functionalised and complex nature of these

compounds, in addition to their intriguing biological activities, it is not surprising that

this class of compounds has stimulated the interest of biologists, pharmacologists, and

synthetic chemists for several years.

3.1.2 Cyclohexenone epoxide natural products SDEF 678 (138) and speciosins

A-F (139-144)

In 2001, the group of Ghisalberti et al. discovered a uniquely substituted cyclohexenone

epoxide containing the 7-oxabicyclo[4.1.0]hept-3-en-2-one moiety.4 Compound 138

was isolated as a secondary metabolite produced in liquid cultures of a fungus (SDEF

678) isolated from the roots of an Australian native grass, Neurachne alopecuroidea,

(Figure 3.02).4 The fungus shows inhibitory activity against phytopathogens and plant

growth promoting activity in vivo.4 SDEF 678 (138) exhibited these same activities

when assayed against the phytopathogen Gaeumannomyces graminis var. tritici (Ggt)*

and in plant growth promotion assays.4

Figure 3.02. Cyclohexenone epoxide 138 is a metabolite produced in liquid cultures of an ectotrophic

fungus (SDEF 678) isolated from the roots of an Australian native grass (Neurachne alopecuroidea).4

* The fungus Gaeumannomyces graminis var. tritici (Ggt) is the cause of a worldwide root disease in

wheat known as "Take-all".259-261

69

At the time of its discovery SDEF 678 (138) was a uniquely monosubstituted*

337-oxabicyclo[4.1.0]hept-3-en-2-one type cyclohexenone epoxide until the discovery

of speciosins A and B (139 and 140) by the group of Jiang et al. in 2009 (Figure 3.03).5

Speciosins A-F (139-144) were isolated as secondary metabolites produced from the

liquid cultures of a fungus (Hexagonia speciosa) found in the tropical and subtropical

zones of China.5

Figure 3.03. speciosins A-F (10-15), isolated as secondary metabolites produced from the liquid cultures

of Hexagonia speciosa: speciosin A (139); speciosin B (140); speciosin C (141); speciosin D (142);

speciosin E (143); speciosin F (144).5,133,263

SDEF 678 (138) and speciosins A and B (139 and 140) are all trisubstituted epoxides

that contain a key 7-oxabicyclo[4.1.0]hept-3-en-2-one moiety substituted with an alkyne

substituent at C1 and a hydroxyl group at C5. Additionally, natural products 138-140

all have the same relative configuration. Other key features of these compounds are the

presence of a bis-substituted cis-double bond and three contiguous stereogenic centres.

Speciosins C-F (141-144) have the same substitution pattern as compounds 138-140,

but contain a 7-oxabicyclo[4.1.0]hept-3-en-2-ol core structure (highlighted in

red, Figure 3.03) and four contiguous stereogenic centres. It was observed that

* A similar regioisomer of 138, known as harveynone (131, Figure 3.04), had been isolated as a

phytotoxic metabolite from the fungus Pestalotiopsis theae (the cause of Grey tea blight). The two

regioisomers 138 and 131 have the same relative configuration.262

Figure 3.04. Harveynone (131).262

70

speciosins C-F (141-144) could potentially be accessed from reduction of their

analogous precursors containing the 7-oxabicyclo[4.1.0]hept-3-en-2-one core structure.

3.1.3 Masked para-benzoquinone ketals as key intermediates in the total

synthesis of cyclohexenone epoxides

Reported in the literature are a number of highly varied methods towards the total

synthesis of cyclohexenone epoxides containing the previously described

7-oxabicyclo[4.1.0]hept-3-en-2-one structural moiety.240,243,264-267

It has been observed

that masked para-benzoquinone ketals, such as 145 and 147 (Scheme 3.01), are key

intermediates common to a number of total syntheses for these type of epoxides.268

Two

examples of natural products synthesised from such para-benzoquinone ketal precursors

are (-)-jesterone (146) and (+)-ambuic acid (137) (Scheme 3.01).269,270

Scheme 3.01. 1) Porco's synthesis of (-)-jesterone (146);269

2) Jungs's synthesis of (+)-ambuic acid

(137).270

Highlighted in red is the masked para-benzoquinone ketal moiety.

para-Benzoquinone ketals serve as important building blocks to cyclohexenone epoxide

containing natural products because they provide the correct functionality to access the

core 7-oxabicyclo[4.1.0]hept-3-en-2-one moiety observed in these structures. This is

done through directed epoxidation, reduction, and ketal deprotection reactions. In

addition, para-benzoquinone ketals can be accessed from a variety of methods through

a number of different precursors (Scheme 3.02).

71

Scheme 3.02. Precursors for the preparation of masked para-benzoquinone ketals.268

As discussed by Magdziak et al.268

methods leading to masked para-benzoquinone

ketals include: the phenolic oxidation of alkoxy phenols (149); the double oxidation of

unsubstituted phenols (151); the selective ketalisation of para-quinones (152); the

oxidation of dialkoxy benzenes (153); and the anodic oxidation of dialkoxy benzenes

(153) to bis-quinone ketals (154), followed by selective de-ketalisation. The most

popular method remains to be the oxidation of phenols in the presence of a nucleophilic

alcohol. A wide variety of metal oxidants have been used for this reaction including

compounds of Fe(III),271

Mn(IV),272

Ag(I),273

Pb(IV),274

Va(IV),275

Ti(III),276

and

Cu(II).277

In recent times, the aforementioned metal reagents are rarely used because of

the development of environmentally benign, easy-to-handle, hypervalent iodine reagents

such phenyliodonium diacetate (PIDA) for phenolic oxidations.

3.1.4 Phenolic oxidations using PIDA as a way to access masked benzoquinone

ketals

The proposed mechanism for the formation of masked para-benzoquinone ketals from

para-substituted phenols is outlined in Scheme 3.03. In the hypothetical pathway,

phenol 155 forms a phenyliodono intermediate (156) with PIDA. The phenyliodono

group* (highlighted in red, Scheme 3.03) then dissociates from the intermediate 156 to

* The phenyliodono group is a powerful nucleofage that has a leaving group ability ~8 × 10

5 times greater

than that of a triflate.278,279

72

give a phenoxenium ion (157/158). The phenoxenium ion then undergoes nucleophilic

attack with an appropriate alcohol to give a benzoquinone ketal (159).

Scheme 3.03. Proposed mechanism for the synthesis of para-benzoquinone ketals with PIDA in the

presence of methanol.271,278-283

The electronic distribution for a phenoxenium ion derived from a para-substituted

phenol is represented by a number of contributing resonance structures in Scheme 3.04.

The regiochemistry of the attack is controlled by electronic effects. Nucleophilic attack

can occur at either the ortho- or para-positions on the phenoxenium ring

(Scheme 3.04).

Scheme 3.04. Contributing resonance forms for the phenoxenium structure, generated from a para-

substituted phenol.278

For substrates with electron-donating substituents at the para-position, preferential

attack almost always occurs at the para-substituted carbon, even if it is the most

hindered site.278

This is because the para-carbon is the most stable position for the

concentration of a positive charge (Scheme 3.04). The ortho-carbon is a less stable

73

position because it is adjacent to an electro-withdrawing group (Scheme 3.04). Despite

this, experiments have shown that ortho-substitution can also occur as a by-product, if

there is an additional electron-donating group at the ortho-position on the ring.278,279

Phenols that are unsubstituted at the ortho- and para-positions on the ring undergo

double oxidation with PIDA (2 equivalents) to give both ortho- and para-benzoquinone

ketals (Scheme 3.05).278

Scheme 3.05. The synthesis of ortho- and para-masked benzoquinone ketals from unsubstituted phenols,

with PIDA.278

The electronic distribution for a phenoxenium ion, derived from an unsubstituted

phenol, is represented by a number of contributing resonance structures in Scheme 3.06.

Initial nucleophilic attack can occur at either the ortho- or para-positions on the ring.

For the reasons described earlier, nucleophilic attack at the para-position is favoured,

with a minor amount also occurring at the ortho-position.284

Upon further reaction with

a second equivalent of PIDA, the ortho-substituted phenol gives an ortho-benzoquinone

ketal (165), and the para-substituted phenol gives a para-benzoquinone ketal (167)

(Scheme 3.05).278

Scheme 3.06. Contributing resonance forms for the phenoxenium structure, generated from an

unsubstituted phenol.

74

After formation of masked benzoquinone ketals with PIDA, the only by-products of the

reaction are acetic acid and iodobenzene.


At the commencement of this project, no methods for the total syntheses of natural

products 138-144 had been developed. Our aim was to develop the first enantioselective

total synthesis of SDEF 678 (138) and then apply this methodology to the synthesis of

speciosins A-F (139-144). We intended to use the synthesised natural products for

further biological investigations. The total synthesis of compound 138 was approached

via two main pathways, these are highlighted in Scheme 3.07.

Scheme 3.07. The total synthesis of SDEF 678 (138). Pathway 1, through key intermediate ketal 172.

Pathway 2, through key intermediate Diels-Alder adduct 174.

3.1.6 Planned synthetic routes to SDEF 678 (138) and speciosins A-F (139-144)

A common approach towards the synthesis of 7-oxabicyclo[4.1.0]hept-3-en-2-one

cyclohexenones containing a trisubstituted epoxide involves inserting the side chain

attached to the epoxide carbon via a cross-coupling reaction.270

This step is followed by

regioselective epoxidation of the trisubstituted alkene, after the less hindered alkene is

blocked following a Diels-Alder reaction (e.g. an approach used in the synthesis of

ambuic acid, Scheme 3.01).270

After the epoxidation, the alkene is regenerated via a

retro-Diels-Alder reaction to re-establish the cyclohex-2-enone moiety observed in the

natural product.

75

Our initial investigations avoided this Diels-Alder/retro-Diels-Alder protecting group

strategy due to the low yields often associated with the latter reaction. Instead, we chose

ketal 172 as a key intermediate in a planned 8-step linear synthesis of cyclohexenone

epoxide 138, devoid of any protecting group manipulations. Exploitation of the allylic

alcohol functionality in ketal 172 was to give regio- and stereo-controlled Sharpless

epoxidation to the cyclohexenone epoxide moiety observed in the natural product. We

then aimed to use the same allylic alcohol functionality as a precursor to the alkyne side

chain observed in SDEF 678 (138) (Scheme 3.07).

The limitations of using the substrate 172 unprotected in our initial investigations

prompted us to also develop a second more conventional synthesis in which the alkyne

side chain was inserted via a Pd-catalysed cross-coupling reaction. Both syntheses are

discussed in more detail in the following sections.

76

77

3.2 Efforts towards the total synthesis of SDEF 678 (138) and

speciosins A-F (138-144)

In our initial investigations, we aimed to synthesise SDEF 678 (138) in 8 steps

beginning with commercially available phenol 175 (Scheme 3.08). Key steps in the

synthesis included: the oxidation of phenol 175 using phenyliodonium diacetate

(PIDA); the Sharpless asymmetric epoxidation of ketal 172, which establishes two of

the three stereogenic centres observed in the natural product; a Corey-Fuchs reaction

which inserts the alkyne functionality via aldehyde 177; and a diastereoselective

diisobutylaluminium hydride (DIBAL-H) reduction that establishes the third chiral

centre using the enantiopure epoxide as a chiral auxiliary.

Scheme 3.08. Retrosynthetic analysis of SDEF 678 (138).

As mentioned earlier, ketal 172 was considered a key intermediate. Thus, the first step

in our approach to achieve the total synthesis of 138 was to find the most efficient way

78

to synthesise ketal 172. Three pathways to obtain 172 were investigated, they are

discussed in more detail below.

3.2.1 The synthesis of ketal 172 - pathway 1

As outlined in Scheme 3.09 the synthetic strategy envisioned for pathway 1 produced

the desired benzoquinone ketal 172 in 2 steps and an overall optimised yield

of 57%. The key reaction was the phenolic oxidation of key intermediate

3-(hydroxymethyl)phenol (175) to give ketal 172. Despite phenol 175 being a

commercially available compound, we found that the most cost effective way to access

175 was from the hydride reduction of 3-hydroxybenzaldehyde (181).

Scheme 3.09. Reagents and conditions: a) i) LiAlH4 (1.1 eq), THF, 0°C, 1 h ii) 63% w/w aq

KNaC4H4O6.4H2O, 2 h, 87%; b) i) PhI(OAc)2 (2.1 eq), MeOH, 0°C to rt, 3 h ii) 9% w/w aq NaHCO3,

2 min, concentrated in vacuo, 65%.

Thus, the synthesis began with benzaldehyde 181 which was reduced to benzylic

alcohol 175 in 87% yield upon treatment with LiAlH4 (1.1 eq) in THF at 0°C, followed

by a workup with 63% w/w aq Rochelle's salt* (Scheme 3.09). Initial attempts at

reducing benzaldehyde 181 with NaBH4, followed by an acidic aqueous workup, only

gave benzylic alcohol 175 in yields below 50%.

Following its synthesis, phenol 175 was subjected to various reaction conditions with

PIDA to give the ketal 172 via phenolic oxidation. The results are summarised in

Table 3.01.

* Aqueous solutions of Rochelle's salt chelate to aluminium and break up emulsions formed from LiAlH4,

thereby making the reduced product easier to extract and isolate.285

79

Table 3.01. Optimisation reactions for the synthesis of ketal 172 from phenol 175.

Entry Conditions† 183 184 185 172

1 a 28% - - -

2 b - 3% 4% 53%

3 c 65%

† a) i) PhI(OAc)2 (2.1 eq), MeOH, 0°C to rt, 3 h ii) 9% w/w aq NaHCO3, 2 min; b) i) PhI(OAc)2 (2.1 eq),

MeOH, 0°C to rt, 3 h ii) 9% w/w aq NaHCO3, 2 min; c) i) PhI(OAc)2 (2.1 eq), MeOH, 0°C to rt, 3 h

ii) 9% w/w aq NaHCO3, 2 min, concentrated in vacuo.

Using a standard literature procedure278

phenol 175 (1 eq) was added to a solution of

PIDA (2.1 eq) and methanol at 0°C (entry 1, Table 3.01). After 3 hours, the reaction

gave rise to 3-hydroxy-2,6-dimethoxybenzaldehyde (183) in 28% yield, instead of the

desired ketal 172. It was predicted that phenol 183 was formed via the mechanism

proposed in Scheme 3.10.

Scheme 3.10. The proposed mechanism for the formation of dimethoxybenzene 183 from phenol 175.

80

In this sequence, the benzylic alcohol was added in portions to an excess of PIDA

stirring in methanol (entry 1, Table 3.01). This caused it to oxidise to benzaldehyde 181

and form the ortho-methoxyphenol 187. We would not have suspected the ortho-

position on the phenoxenium ion intermediate to be preferentially methoxylated due to

the instability of having a positive charge concentrated on a carbon atom in such close

proximity two electron-withdrawing carbonyl groups. However, it was likely that this

position on the ring was also the most electrophilic and the most susceptible to

nucleophilic attack.

After reaction of ortho-methoxy phenol 187 with PIDA to form another phenoxenium

ion intermediate, we predicted that the more stable para-position was now the favoured

site for nucleophilic attack. It was likely that the ortho-carbon lacked its previous

reactivity due to stabilisation by a methoxy substituent. Thus, it was predicted that

phenol 187 was methoxylated after reaction with PIDA, to give the labile benzoquinone

ether 182, which underwent spontaneous rearrangement to give dimethoxy phenol 183.

Ketal 172 could not be synthesised when phenol 175 was added to PIDA (entry 1,

Table 3.01). However, when the procedure was modified so that PIDA was added to a

stirring solution of phenol 175 in methanol at 0°C for 3 hours, ketal 172 was

synthesised in varying yields, depending on the choice of workup procedure (entries 2

and 3, Table 3.01). A modest yield of 53% for ketal 172 was achieved after the reaction

mixture was quenched with 9% w/w aq NaHCO3, stirred for 2 minutes, and then

extracted with EtOAc (entry 2, Table 3.01). A much higher yield of 65% for ketal 172

was achieved when the reaction mixture was quenched with 9% w/w aq NaHCO3,

stirred for 2 minutes, and then extracted with EtOAc, after the methanol was removed

from solution (entry 3, Table 3.01). The phenolic oxidation using phenol 175 and the

conditions specified in entry 3 (Table 3.01) could be scaled-up to produce 3 g of ketal

172.

Analysis of the spectroscopic data indicated the synthesis of 172. The IR spectrum

showed a characteristic OH bond absorption band at 3447 cm-1

and a carbonyl bond

absorption band at 1678 cm-1

. Detailed examination of the 1H NMR revealed a typical

pattern for a 1,2,4-trisubstitued benzoquinone ketal ring i.e. the three signals of an AMX

spin system at δ = 6.78, 6.51, and 6.42 (Jortho = 10.3, Jmeta = 2.2, Jpara = 0 Hz).

Characteristic signals of an allylic alcohol group were also present at δ = 4.41 (CH2OH)

81

and 2.29 (CH2OH). Particularly diagnostic for the synthesis of benzoquinone ketal 172

was the appearance of a resonance signal in the 1H NMR spectrum at δ = 3.27 (6H),

which was assigned to the dimethoxy ketal protons, and the appearance of a high-

intensity singlet at δ = 185.3 in the 13

C NMR spectrum, which was assigned to the

benzoquinone carbonyl carbon.

3.2.2 The synthesis of ketal 172 - pathway 2

The synthetic strategy for 172 envisioned in an alternative pathway relied on the

phenolic oxidation of 3-(hydroxymethyl)-4-methoxyphenol (190) with PIDA as the key

transformation step (Scheme 3.11). However, phenol 190 is not a commercially

available compound and the simplest way we could devise to synthesise it was from the

reduction of 5-hydroxy-2-methoxybenzaldehyde (184). Thus, our first step was to find

the most efficient route to synthesise benzaldehyde 184.

Scheme 3.11. Retrosynthetic analysis of ketal 172.

The synthesis of 5-hydroxy-2-methoxybenzaldehyde (184):

After a thorough literature search, two viable methods for the synthesis of benzaldehyde

184 were found. In the first, the Anderson synthesis, compound 184 was prepared via a

Pd-catalysed nucleophilic aromatic substitution of commercially available 5-bromo-2-

methoxybenzaldehyde (191), in 93% yield (Scheme 3.12).286

Despite the synthesis

being efficient and high yielding, with a reasonably inexpensive starting material, the

high cost of the ligand 192 deterred us from this method for our initial investigations.

82

Scheme 3.12. The Anderson synthesis of 5-hydroxy-2-methoxybenzaldehyde 184.286

Reagents and conditions: a) Pd2(dba)3 (2 mol%), 192 (8 mol%), KOH (4 eq), H2O/dioxane (1:1), 80°C,

18 h, 93%.286

The second alternative was a synthesis developed by Ulrich et al.287

The procedure

involved the selective demethylation of dimethoxybenzaldehyde 193 at the more

nucleophilic methoxy group meta to the aldehyde, after stirring in concentrated sulfuric

acid, to give benzaldehyde 184 in 42% yield (Scheme 3.13).287

The reaction did not go

to completion and a mixture of the starting material 193 (20% yield) and product 184

(68% based on recovered starting material) were isolated.*

Scheme 3.13. The Ulrich synthesis of 5-hydroxy-2-methoxybenzaldehyde 184.287

Reagents and conditions: a) conc. H2SO4, 52°C, 48 h, 42%, (68% conversion yield).

Considering the poor conversion rate for the selective demethylation of

dimethoxybenzaldehyde 193 to phenol 184,† with sulfuric acid (Scheme 3.13),

numerous attempts were made to improve the selectivity, yield, and conversion rate of

the ether cleavage by using alternative Brønsted-acids, and the addition of methyl

scavengers. The results are summarised in Table 3.02.

* The mixture of starting material 193 and product 184 were easily separated following a wash with 5%

w/w aq NaOH. † We believed the reaction mechanism involved protonation of the methoxy group, followed by an SN2

substitution with HSO4-.

83

Table 3.02. Optimisation of the selective demethylation conditions for the conversion

of dimethoxybenzaldehyde 193 to phenol 184

Entry Conditions† 193 194 184

1 a 12% - 19%

2 b - - 34%

3 c 10% 4% 12%

4 d 16% - 27%

5 e 6% 7% 17%

6 f - - 16%

7 g - - 31%

† a) conc. H2SO4, 90°C, 48 h; b) conc. H2SO4, methionine (1.3 eq), 54°C, 48 h; c) CH3SO3H (20 eq),

methionine (1.3 eq), rt, 3 days; d) conc. H2SO4, NaI (1.2 eq), 54°C, 48 h; e) HBr (48%), 54°C, 18 h;

f) HBr (48%), methionine (1.3 eq), 54°C, 48 h; g) HBr (48%), NaI (1.5 eq), 54°C, 18 h.

Despite trialling a number of alternative reaction conditions, the yield for the synthesis

of phenol 184 from dimethoxybenzene 193 could not be improved above a conversion

yield of 68%. Attempts to improve the conversion rate of substrate to product, through

an increase in reaction temperature resulted in increased decomposition of the reaction

mixture (entry 1, Table 3.02). Many alternative conditions using different Brønsted-

acids, and the addition of methyl scavengers did not show any selectivity for the desired

phenol 184 (entries 3,4, an 5, Table 3.02).

In many cases, the use of a methyl scavenger (methionine or NaI) in conjunction with a

Brønsted-acid (H2SO4, HBr) showed nearly quantitative cleavage of

dimethoxybenzaldehyde 193 to phenol 184 (entries 2, 6, and 7, Table 3.02). However,

the product 184 could not be isolated in quantitative yields. We can only assume, given

the harsh acidic conditions, and aqueous workup methods, that the product was lost due

to undesirable side reactions. It was possible that the aldehyde was being oxidised or

hydrolysed and lost to the aqueous layer as its more water-soluble carboxylic acid or

diol derivative. Alternatively, loss of yield could have been due to polymerisation

reactions occurring in the strongly acidic conditions. We decided to continue our

84

synthesis using the Ulrich conditions because they remained the highest yielding

(68% conversion yield).

The synthesis of benzylic alcohol 190:

With benzaldehyde 184 in hand, it was possible to synthesise 3-(hydroxymethyl)-4-

methoxyphenol (190). Benzylic alcohol 190 was synthesised in a high yield of 91% via

the reduction of benzaldehyde 184 with LiAlH4 in THF at 0°C, followed by a workup

with 63% w/w aq Rochelle's salt (Scheme 3.14).


KNaC4H4O6.4H2O, 20°C, 2 h, 91%.

After we had synthesised para-methoxyphenol 190, it was possible to synthesise ketal

172. Using a modified literature procedure, PIDA was added to a stirring solution of

phenol 190 in methanol at 0°C.278

After 3 hours the reaction gave rise to ketal 172 and

varying mixtures of by-products, depending on the method of workup used. The most

consistently high yields for ketal 172 were achieved when the reaction mixture was

quenched with 9% w/w aq NaHCO3 (2 mL), stirred for 2 minutes, then extracted with

EtOAc after the methanol was removed from solution. These conditions provided ketal

172 in yields of up to 73% (Scheme 3.15).

85

Scheme 3.15. Reagents and conditions: a) conc. H2SO4, 54°C, 48 h, 68% (conversion yield); b) i) LiAlH4

(1.1 eq), THF, 0°C, 1 h ii) 63% w/w aq KNaC4H4O6.4H2O, 20°C, 2 h, 91%; c) i) PhI(OAc)2 (1.1 eq),

MeOH, 0°C to rt, 3 h ii) 9% w/w aq NaHCO3, removed methanol in vacuo, 73%.

In conclusion, pathway 2 starting from dimethoxybenzaldehyde 193 produced the

desired benzoquinone ketal 172 in 3 steps and an overall yield of 45%, after

optimisation (Scheme 3.15). In addition, ketal 172 was easy to separate from

benzaldehyde 184 (the by-product of the reaction) via standard column

chromatography. The optimised phenolic oxidation using phenol 190 could be scaled-up

to produce 4 g of ketal 172.

3.2.3 The attempted synthesis of ketal 172 - pathway 3

A few cases have been observed where dimethoxy benzaldehydes have been oxidised to

masked para-benzoquinone ketals with PIDA, in one step.265,268

As outlined in

Scheme 3.16 the synthetic strategy envisioned for pathway 3 relied on the oxidation of

(2,5-dimethoxyphenyl)methanol (195) with PIDA as the key transformation to

synthesise ketal 172.

86


KNaC4H4O6.4H2O, 20°C, 2 h, 93%; b) PhI(OAc)2 (1.1 eq), MeOH, reflux, 18 h.

The synthesis began with dimethoxybenzaldehyde 193 which was reduced to benzyl

alcohol 195 in 91% yield with lithium aluminium hydride (1.1 eq) in THF at 0°C,

followed by a workup with 63% w/w aq Rochelle's salt (Scheme 3.16).

Following its synthesis, key intermediate dimethoxybenzene 195 was subjected to

various reaction conditions with PIDA in an attempt to obtain ketal 172 via oxidation

(Scheme 3.16). Unfortunately, after several attempts modifying the equivalents of

PIDA, temperature, and time dimethoxybenzyl alcohol 195 was not reactive enough to

synthesise ketal 172. Thus, the approach to ketal 172 through pathway 3 was not

investigated further. Instead ketal 172 was synthesised using pathways 1 and 2. Pathway

1 had fewer steps and produced a higher overall yield of the desired ketal, but pathway

2 was easier to scale-up and purify at the phenolic oxidation stage.

3.2.4 The synthesis of epoxide 176

The epoxidation of ketal 172 was considered a key step in our synthesis because it

would examine for the first time whether or not a benzoquinone ketal intermediate

could be regioselectively and stereoselectively epoxidised without the need for a Diels-

Alder reaction to mask one of the quinone double bonds. Allylic alcohol ketal 172 was

chosen specifically as a key intermediate so that the Sharpless asymmetric epoxidation

conditions could be used to stereo- and regio-selectively insert an epoxide at the

trisubstituted double bond (Scheme 3.17).

87

Scheme 3.17. Retrosynthetic analysis of epoxy alcohol 176.

The Sharpless epoxidation is the premier method for the synthesis of chiral epoxy

alcohols from primary and secondary allylic alcohols.288

The reactive species is a

complex that forms between titanium tetraisopropoxide (Ti-(O-iPr)4), a chiral dialkyl

tartrate (usually (±)-DET or (±)-DIT), an allylic alcohol substrate, and the oxidising

agent tert-butyl hydroperoxide (t-BHP).288

A number of putative transition states are

depicted in the literature.289

The choice of chiral isomer for the dialkyl tartrate

establishes which face the oxidant approaches the allylic alcohol and thus determines

the chirality of the corresponding enantiopure epoxide produced (Scheme 3.18).

Different allylic alcohols coordinate in the same way to the titanium.*288

Scheme 3.18. Enantioselectivity in the Sharpless epoxidation.55,288

Given that electrophilic t-BHP is used as the oxidizing agent, electron-rich alkenes are

generally more reactive than electron-poor alkenes. This was of particular concern to us

because the alkene we were attempting to epoxide was conjugated with a carbonyl

group and these types of alkenes do not generally epoxidise efficiently with

electrophilic oxidants. Despite this concern, we trialled a number of conditions using

the Sharpless protocol to try and optimise the yield of epoxide 176.

For our trial reactions, many of the parameters were kept constant. In all cases, a

mixture of Ti(O-iPr)4, the dialkyl tartrate, allylic alcohol 172 (1 eq), CH2Cl2,† and 4Å

* The Sharpless epoxidation and its mechanism are discussed thoroughly in the chemical

literature.55,288-290

† Dichloromethane is the solvent of choice for Sharpless epoxidation reactions because it does not hinder

the rate of reaction unlike alcohols, ketones and other coordinating solvents.291

88

molecular sieves were stirred together at -20°C*, for 30 minutes, to prepare the reactive

complex. After this catalyst "aging" period t-BHP (1.5 to 2 equivalents)† was added to

complete the epoxidation process and the reaction mixture was left to stir.

Also, it was discovered by Sharpless et al. that a ratio of 1:>1 of Ti(O-iPr)4 to dialkyl

tartrate is better for the enantioselectivity of the reaction than a 1:1 ratio of the two

reagents.290

Thus, the recommended ratio of Ti(O-iPr)4 to dialkyl tartrate (1:1.2) was

kept consistent throughout all the reaction conditions trialled.290,291

Additionally, all of

our trial reactions were performed at substrate concentrations of 0.4 M in CH2Cl2 which

is recommended for clean epoxidations with minimal side-reactions.290,291

Crushed,

flame dried 4 Å molecular sieves were also added to all reactions to remove any water

present, which can affect the yield and enantioselectivity of the epoxide produced.290,291

Many other substrate dependant parameters of the Sharpless epoxidation such as the

equivalents of catalyst and reagents, the reaction temperature, the reaction time, and

workup procedure were altered when trying to optimise the yield of epoxide 176. These

results are summarised in Table 3.03.

* It has been stated that the reactive complex is not stable above temperatures of 0°C prior to epoxidation,

thus the reactive complex was always prepared at temperatures around -20°C.290,291

† The recommended number of equivalents of t-BHP to attain reasonable reaction rates is between 1.5 and

2 equivalents.291

89

Table 3.03. Optimisation of the Sharpless epoxidation for the synthesis of epoxide 176:

Reagents and conditions: Ti(O-iPr)4, tartrate, t-BHP, temp, time, workup.

Entry Ti(O-iPr)4 (+)-DET (+)-DIT t-BHP Temp Time Workup 176

1 1 eq 1.2 eq - 1.5 eq -20°C 18 h A NR

2 1 eq 1.2 eq - 1.5 eq -20°C to 0°C 18 h A NR

3 1 eq 1.2 eq - 1.5 eq -20°C to 20°C 18 h A 6%

4 1 eq - 1.2 eq 1.5 eq -20°C to 20°C 18 h A 32%

5 1 eq - 1.2 eq 1.5 eq -20°C to 20°C 48 h A 28%

6 1 eq - 1.2 eq 1.5 eq -20°C to 20°C 18 h B 38%

7 1 eq - 1.2 eq 1.5 eq -20°C to 20°C 18 h C 41%

8 1 eq - 1.2 eq 2 eq -20°C to 20°C 18 h C 44%

9 0.2 eq 0.24 eq 2 eq -20°C to 20°C 18 h C NR

10 0.5 eq 0.6 eq 2 eq -20°C to 20°C 18 h C 35%

NR = no reaction

90

For our first trial epoxidation reaction (entry 1, Table 3.03) a stoichiometric

combination of Ti(O-iPr)4, (+)-DET, allylic alcohol 172, and t-BHP was left to stir at

-20°C for 18 hours. Regrettably, the substrate was not sufficiently reactive enough for

epoxidation to occur at this temperature. As a result, the reaction conditions were

repeated and the mixture was allowed to warm to 0°C and then stirred for 18 hours

(entry 2). However, at this increased reaction temperature none of the desired product

176 was produced. In a third attempt, the stoichiometric reaction conditions were

repeated, but this time the reaction mixture was allowed to warm to room temperature,

and then stirred for 18 hours (entry 3). The increased reaction temperature, in

conjunction with workup A,* produced the desired epoxy alcohol in 6% yield, with a

large amount of unreacted substrate remaining.

In the next set of conditions (entry 4) the tartrate ester was changed from (+)-DET to

(+)-DIT, while all the other reaction parameters were kept constant relative to entry 3.

(+)-DIT gave a significantly higher conversion to epoxide 176 relative to (+)-DET.

However, a large proportion of the substrate still remained unreacted. In an effort to

allow the reaction to go to completion, the reaction time was increased from 18 hours to

48 hours, while all the other reaction parameters were kept constant (entry 5).

Unfortunately, the increased reaction time decreased the yield of epoxide 176, and the

reaction was messier due to decomposition of the starting material 172 and product 176.

The highest yield of product obtained in conjunction with workup A was 32%. We

believed that the low yields observed were in part due to hydroxide mediated ring

opening (from the NaOH wash) of the epoxide at C1, facilitated by the carbonyl group.

As a result, the NaOH was removed from workup A in the next set of trial conditions

(workup B). The conditions using workup B, provided epoxide 176 at an improved

yield of 38% (entry 6).

We also trialled a workup method recommended for acid sensitive, water soluble

epoxide products using Na2SO4, as described by Sharpless (workup C).290,292

This

workup improved the yield of the epoxide to 42% (entry 7). Additionally, a slight

increase of the t-BHP from 1.5 to 2 equivalents further improved the yield of epoxide

176 to 44% (83% conversion yield) (entry 8).

* Workups A, B, and C are described in detail in the experimental section.

290

91

Considering we had optimised the reaction conditions for a stoichiometric ratio of

catalyst, we decided to trial smaller catalyst loadings. Unfortunately, reducing the

catalyst to 0.25 equivalents (entry 9) failed to produce any of the desired epoxide, and

reducing the catalyst to 0.5 equivalents reduced the yield from 44% to 35% (entry 10).

Thus, after optimisation, epoxide 176 was produced from allylic alcohol 172 in 83%

yield (based on recovered starting material). The Sharpless epoxidation using ketal 172

could be scaled-up to produce 2 g of epoxide 176. Chiral HPLC determined the

enantiomeric excess to be 72%. No further investigations were made to determine

which enantiomer was formed in excess. However, literature proposed by Sharpless et

al. (Scheme 3.18)55,288

suggests the formation of isomer 176a in excess (Figure 3.05).

Figure 3.05. Isomer 176a.

Particularly diagnostic for the synthesis of epoxide 176 was the appearance of a

resonance signal at δ = 3.48 (J = 2.0 Hz) in the 1H NMR that was assigned to the

oxymethine proton at H-1. This signal also showed coupling to a resonance signal at

δ = 6.10 (J = 2.0 Hz) which was assigned to the proton at H-3. A key resonance signal

in the 13

C NMR spectrum at δ = 53.7 was also assigned to the oxymethine carbon.

The Sharpless epoxidation provided the epoxide 176 in a fairly high conversion yield of

83%, however, we wanted a cheaper more facile method to access larger quantities of

epoxide 176 for trial reactions. Thus, we applied a number of well-established methods

for the epoxidation of allylic alcohols comprising the epoxidising agents VO(acac)2/

t-BHP (also proposed by Sharpless),293,294

m-CPBA,295

and Ti(O-iPr)4/t-BHP towards

the synthesis of racemic 176. Like the Sharpless epoxidation these are all electrophilic

epoxidation methods. The first approach utilised m-CPBA and produced none of the

expected product. Instead, no reaction occurred and the starting material was re-isolated

(Scheme 3.19).

92

Scheme 3.19. Reactions and conditions: a) m-CPBA (1 eq), NaHCO3 (1.3 eq), CH2Cl2, 0°C, 16 h, no

reaction.

The use of catalytic amounts of VO(acac)2 and Ti(O-iPr)4 in the presence of t-BHP also

failed to produce any of the desired product. These conditions did, however, produce

quinone 196 via a Lewis-acid promoted deprotection of the ketal group (Scheme 3.20).

Scheme 3.20. Reactions and conditions: a) VO(acac)2 (5 mol%), t-BHP (1.2 eq), CH2Cl2, 0°C, 1 h, 33%;

b) VO(acac)2 (5 mol%), t-BHP (1.2 eq), CH2Cl2, 0°C, 1 h, 29%.

As a result, the total synthesis was continued with the previously described optimised

Sharpless epoxidation conditions (entry 8, Table 3.03). The spectroscopic data for

quinone 196 matched that reported previously in the literature.296

3.2.5 The attempted synthesis of ketal alcohol 200

Despite the high conversion yield for the Sharpless epoxidation (83%), the reaction was

not efficient using this electrophilic epoxidation method. Unfortunately, with ketal 172

as a precursor, the type of epoxidation methods that could be trialled were limited.

Nucleophilic asymmetric epoxidation conditions297-301

were not viable options due to

the presence of two epoxidisable benzoquinone alkenes and because ketal 172

aromatises to 5-hydroxy-2-methoxybenzaldehyde (184) when exposed to base or

nucleophiles (Scheme 3.21).

93

Scheme 3.21. Proposed mechanism for the synthesis of 5-hydroxy-2-methoxybenzaldehyde 184 from

ketal 172 with base.

Additionally, we desired the regioselectively and stereoselectively provided by the

Sharpless protocol. Hence, it was decided that the carbonyl group would be masked in

an effort to improve the enantioselectivity and yield of the Sharpless epoxidation

reaction.

Our initial attempts to mask the carbonyl group of benzoquinone ketal 172 focused on

reduction of the carbonyl to form ketal alcohol 200 (Scheme 3.22). We were not

concerned about the regioselectively of the potential epoxidation reaction, despite the

presence of two allylic alcohol groups, because cis-substituted primary allylic alcohols

are more reactive towards epoxidation via the Sharpless protocol than secondary allylic

alcohols embedded in a ring system.291

Scheme 3.22. Retrosynthetic analysis of epoxide 199.

94

In the past, reduction reactions of benzoquinone ketals have only been successful on

highly sterically hindered ketals with sodium borohydride.302

Sterically hindered

benzoquinone ketals can be reduced to hydroxy ketals because they are thermally stable

at room temperature due to their reluctance to spontaneously decompose to their alkoxy

phenol derivatives. This is because formation of the planar t-Bu-C=C-OR skeleton in

the phenol (highlighted in red, Scheme 3.23) is not favoured due to steric repulsion

between the tertiary butyl groups and R group of the alkoxy ether.302

Scheme 3.23. The reduction of sterically hindered benzoquinone ketal 201

to thermally stable sterically hindered hydroxy ketal 202 via the Omura conditions.

Reagents and conditions: a) i) NaBH4 (5 eq), DME/H2O (5:2), rt, 50 min ii) 1 M aq AcOH, ~pH 3-4,

98%;302

On the other hand, reduction of simple benzoquinone ketals give labile hydroxyl ketals

(206) which spontaneously eliminate an alcohol to give para-alkoxy phenols (207)

(Scheme 3.24).

Scheme 3.24. Reagents and conditions: a) NaBH4 (5 eq), DME/H2O (5:2), rt.

Thus, our first step was to protect the primary alcohol on 172 to make a more sterically

hindered benzoquinone ketal that would potentially be more stable to hydride reduction

95

conditions (Scheme 3.25). For these reasons, TBDMS was chosen as a protecting group

and we proposed two main pathways to give the desired benzoquinone ketal 209.

Scheme 3.25. Retrosynthetic analysis of benzoquinone ketal 201 via pathway 1.

For pathway 1, the first step was to synthesise 212 from hydroxymethyl phenol 175

(Scheme 3.26). It was claimed in the literature that treating a hydroxyalkyl phenol with

TBDMSCl, NEt3, and a catalytic amount of DMAP in CH2Cl2 at 0 °C, would give

selective protection at the primary hydroxyl group.303

Unfortunately, exposing

hydroxymethyl phenol 175 to the conditions described gave a mixture of mono- and di-

protected silyl derivatives (210-212), with the desired phenol 212 produced only in 39%

yield (Scheme 3.26). This was followed by oxidation of phenol 212 with PIDA to give

the desired ketal 209 in a low yield of 43% (Scheme 3.26).

96

Scheme 3.26. Reagents and conditions: a) TBDMSCl (1.1 eq), NEt3 (1.5 eq), CH2Cl2, DMAP (5 mol%),

0°C, 3 h, 210 (17%), 212 (39%), 211 (8%); b) PhI(OAc)2 (1.1 eq), MeOH, 0°C to rt, 3 h ii) 9% w/w aq

NaHCO3, 209 (43%).

Due to the low yield for the synthesis of 209 via pathway 1, an alternative synthetic

approach was pursued. Thus, ketal 172 was treated with TBDMSCl, NEt3 and a

catalytic amount of DMAP in dichloromethane at 0 °C for 3 hours to give the desired

protected benzoquinone ketal 209 in a yield of 79% (Scheme 3.27).

Scheme 3.27. Reagents and conditions: a) TBDMSCl (1 eq), NEt3 (2.2 eq), CH2Cl2, DMAP (5 mol%),

0°C, 3 h, 79%.

It was unknown if the TBDMS protected ketal 209, would be sterically hindered enough

to prevent spontaneous elimination of methanol to give hydroxyl ketal 208. Despite our

concerns, however, ketal 209 was exposed to various reduction conditions in an attempt

97

to synthesise 208. The results are summarised in Table 3.04. The reaction conditions

trialled included: the Omura reaction conditions that were used for the reduction of

sterically hindered ketal 201 (entry 1, Table 3.04); a standard NaBH4 reduction using

conditions that have worked previously in the literature for a sterically hindered ketal

(entry 2);304

a Luche reduction (entry 3); and a standard LiAlH4 reduction (entry 4).

Table 3.04. Attempted reduction of ketal 209 to hydroxy ketal 208

Entry Conditions† 208 213 214

1 a 0%

2 b 0% 63% 0%

3 c 0% 98% 0%

4 d 0% 18% 27%

† a) i) NaBH4 (5 eq), DME/H2O (5:2), rt, 50 min ii) 1 M aq AcOH, ~pH 3-4;302

b) NaBH4 (1 eq),

CH2Cl2/MeOH (1:1), 0°C, 30 min, 87%.304

; c) NaBH4 (1 eq), CeCl3.7H2O (1.2 eq), MeOH, 0°C, 1 h;

d) LiAlH4 (1 eq), THF, 0°C, 30 min.

To our dismay, all the reduction conditions trialled gave the phenol 213. The Luche

reduction produced phenol 213 in the highest yield of 98% (entry 3, Table 3.04). Given

the proposed mechanism for the Luche reduction, we predicted that a labile hydroxyl

ketal formed (216), and then spontaneously eliminated methanol to give phenol 213

(Scheme 3.28). Exposing ketal 209 to standard LiAlH4 reduction conditions gave

phenol 213 in 18% yield, and a 1,4-reduction product that we suspected was 214 in 27%

yield (entry 4, Table 3.04).

98

Scheme 3.28. Proposed mechanism for the synthesis of phenol 213 from the Luche reduction

conditions.305,306

Given that ketal alcohol 208 could not be synthesised by reducing ketal 209, the

synthetic sequence involving hydroxyl ketal 208 was abandoned. As this reduction

would not have been diastereoselective, epoxidation of hydroxyl ketal 208 would have

led to a mixture of anti-syn diastereoisomers which would have complicated future

steps. Thus, further investigations were made to find a more efficient protecting group

strategy to mask the benzoquinone ketal carbonyl group.

3.2.6 The attempted synthesis of bisketal 224

Many of the suggested methods for masking a carbonyl functionality involve an acetal

or ketal protecting group.307

We were concerned about the suitability of a second ketal

protecting group because this would remove the selectivity from our protecting group

strategy and would provide a cyclohex-2-ene-1,4-dione moiety (222) instead of the

desired 4-hydroxycyclohex-2-enone moiety (223) (Figure 3.06).

99

Figure 3.06. The cyclohex-2-ene-1,4-dione moiety (222) and the 4-hydroxycyclohex-2-enone moiety

(223).

Upon further investigation however, a literature search revealed that a number of natural

product precursors with cyclohex-2-ene-1,4-dione moieties (222) have been

regioselectively reduced to give a natural product with a 4-hydroxycyclohex-2-enone

moiety (223).308

However, these precursors relied on the coordination of aluminium

with a methyl hydroxyl group at C4 and the adjacent carbonyl group to activate the

carbonyl carbon towards regioselective reduction (Scheme 3.30).

Scheme 3.30. Partial synthesis of epi-yanuthone A (221).308

Reagents and conditions: a) DIBAL-H (2 eq), THF, -78°C; b) 63% w/w aq KNaC4H4O6.4H2O, 20°C,

71%.308

In the absence of a methyl hydroxyl group at C4 it was unsure if this same selectivity

would occur. Despite this, we planned a new synthetic sequence in which diketal 224

was proposed as a key intermediate (Scheme 3.31). It was hoped that reduction of the

quinone derivative 227 would regioselectively occur at ketal C4 because it is less

hindered by an adjacent bulky side chain (Scheme 3.31).

100

Scheme 3.31. A proposed route to SDEF 678 138 through dimethoxybenzene 195.

The first step in the synthetic sequence was to synthesise the quinone bisketal 224. The

most common way to synthesise quinone bisketals is via single-cell anodic oxidation of

1,4-dimethoxybenzenes.309

Regrettably, the equipment required to synthesise bisketal

224 via anodic oxidation was unavailable to us, so we had to pursue alternative routes to

244. As a result, we trialled a number of typical carbonyl ketalisation procedures using

benzoquinone ketal 172 as a substrate. These results are summarised in Table 3.05.

Table 3.05. The attempted synthesis of bisketal 224.

Entry Conditions† 196 224

1 a 59% 0%

2 b Complex mixture

3 c 13% 0%

4 d Complex mixture

5 e Complex mixture

† Reagents and conditions: a) MeOH (2 eq), BF3·Et2O (1.5 eq), DME, rt, 1 h; b) BF3·Et2O (2 eq), MeOH,

0°C, 30 min; c) BF3·Et2O (2.5 mol%), MeOH, 0°C, 30 min d) conc. H2SO4, 0°C, rt, 2 h; e) p-TsOH,

ethylene glycol, 0°C, 2 h.

101

Due to the base sensitive nature of our substrate the conditions we trialled had to be

limited to Lewis- or Brønsted acid-promoted ketalisation procedures. Unfortunately,

treatment of ketal 172 with various Lewis acids including boron trifluoride diethyl

etherate and concentrated sulfuric acid (even in catalytic amounts) led to the

formation of quinone 196 (entry 1, Table 3.05) or a complex mixture (entries 2

and 3, Table 3.05). Bisketal 224, could not be synthesised so this pathway was not

investigated further.

3.2.7 The attempted synthesis of ketal alcohol 239

The carbonyl group of a benzoquinone ketal can undergo 1,2-addition reactions with a

variety of organolithium reagents, without re-aromatisation, to give tertiary alcohols.

Quite often, 1,2-additon reactions to a carbonyl group are irreversible. However, a

method was developed by Ohta et al. in which treatment of a carbonyl compound with

1-methyl-2-lithio-1H-imidazole (229) masks the carbonyl by forming a 1-methyl-2-(1'-

hydroxyalkyl)-1H-imidazole group (highlighted in red, Scheme 3.32).310

The carbonyl

is easily regenerated from the quaternisation of the imidazole with methyl iodide,

followed by basic aqueous treatment (Scheme 3.32).310

The imidazole moiety was

found to be stable under harsh reaction conditions.310

Scheme 3.32. Masking of carbonyl group by 1-methyl-1H-imidazole.310

102

Thus, we envisaged imidazole 239 as a key intermediate in an alternative protecting

group strategy for the carbonyl group, to eventually improve the electronics of the

epoxidation step (Scheme 3.33).*

Scheme 3.33. Reagents and conditions: a) i) 237 (1 eq), n-BuLi (1 eq), THF, -78°C, 1 h ii) 37% w/w aq

NH4Cl, 98%; b) TBAF (1.2 eq), THF, rt, 1 h, mixture, major product could not be isolated.

Thus, ketal 201 was exposed to standard literature conditions with n-BuLi and

imidazole 237 to give tertiary alcohol 238 in 98% yield (Scheme 3.33). Particularly

diagnostic for the synthesis of 238 were the appearance of resonance signals in the 1H

NMR spectra assigned to imidazole protons at δ = 6.90 and 6.80 ppm.

Regrettably, attempted de-protection of the TBDMS group with TBAF under

standard literature conditions311

gave an inseparable mixture of compounds

(step b, Scheme 3.33). Considering that allylic alcohol 239 could not be synthesised

or isolated, this pathway was not considered feasible and was not investigated further.

* A number of alternative protecting groups including cyanohydrins (233 and 234), substituted

hydrazones (235) and substituted oxime derivatives (236) (Figure 3.07) were not considered suitable

because they did not decrease the electrophilic nature of the allylic alcohol or make it more susceptible to

electrophilic epoxidation.

Figure 3.07. Protection for the carbonyl group via miscellaneous derivatives.307

103

3.2.8 The synthesis of aldehyde 177

Unable to optimise the Sharpless epoxidation reaction, we continued our synthesis using

epoxide 176 to synthesise carbaldehyde 177. Carbaldehyde 177 is a key intermediate in

the reaction pathway because the aldehyde group can be used to generate the required

alkyne side chain (retrosynthesis, Scheme 3.08). There are a number of methods for the

selective oxidation of a primary alcohol to an aldehyde.312

Given the highly reactive,

and hence sensitive nature of our cyclohexenone epoxide precursor, we needed a highly

chemoselective, mild and efficient oxidising agent. Thus, 2-iodoxybenzoic acid (IBX)

was our oxidising reagent of choice.313-318

Treatment of the primary alcohol 176 with 3 equivalents of IBX suspended in ethyl

acetate, at reflux, led to the sole formation of aldehyde 177 in 85% yield

(Scheme 3.34).314,316

Scheme 3.34. Reagents and conditions: a) IBX (3 eq), EtOAc, reflux, 5 h, 177 (85%).

Initially, alcohol 176 was treated with 1.1 equivalents of IBX. However, under these

conditions we found that the reaction did not go to completion and a mixture of the

aldehyde 177 and the substrate 176, resulted. After, increasing the number of

equivalents of IBX to 3, the reaction went to completion in a shorter period of time.

The spectroscopic data immediately indicated that the product was aldehyde 177.

Particularly diagnostic for the formation of 177 was the appearance of a resonance

signal observed at δ = 10.17 ppm in the 1H NMR which was assigned to the aldehyde

proton.

104

3.2.9 The synthesis of terminal alkyne 179

As mentioned earlier aldehyde 177 was a key intermediate in the proposed synthesis of

the alkynyl isopropylene side chain for the natural product SDEF 678 (138)

(Scheme 3.35). The extension of a carbonyl group by one carbon to form an alkyne is a

well-known and widely used protocol in organic chemistry.319

We planned to test out a

number of well-established one carbon homologation methods for the synthesis of

terminal alkyne 179 from aldehyde 177. The results are summarised below.

Scheme 3.35. Retrosynthetic analysis of alkyne 180.

Pathway 1 - attempted Bestmann-Ohira reaction:

The Bestmann-Ohira (BMO) reaction is essentially a modified version of the Seyferth-

Gilbert homologation.319-325

Both reactions proceed via the reactive anionic dimethyl

diazomethylphosphonate intermediate 244. However, the BMO reagent (243) provides a

more convenient method to access this intermediate under milder reaction conditions

and without the use of a strong base. The reaction is mechanistically believed to proceed

as illustrated in Scheme 3.36.

105

Scheme 3.36. The proposed mechanism for the synthesis of terminal alkynes from aldehydes via the

Bestmann-Ohira reaction protocol.319

Initially, the anion 244 is generated in situ from the acyl cleavage of the BMO reagent*

by methoxide ions produced in solution. The anion 244 then adds to the aldehyde

carbonyl to form an alkoxide ion that upon further reaction gives rise to an

oxaphosphetane intermediate (248). A syn-cycloelimination from the oxaphosphetane

248 gives a dimethyl phosphate anion (249) and a diazoalkene (250). Loss of nitrogen

from the diazoalkene 250 gives rise to a vinylidene carbene (251) which forms the

terminal alkyne 253 after 1,2-migration of the R substituent.319

* The BMO reagent was synthesised in two steps using the conditions developed by Pietruszka et al.

(Scheme 3.37). The key step was the diazo transfer from tosyl azide 256 to the commercially available

oxophosphonate 257 to give the BMO reagent (243) in 73% yield (56% overall yield).322

Scheme 3.37. Pietruszka's synthesis of the BMO reagent (243). Reagents and conditions: a) NaN3 (1.3 eq), H2O/acetone (1:3), rt,

18 h, 77% (256); b) NaH (1 eq), 256 (1 eq), 257 (1 eq), toluene/THF (3:1), 0°C to rt, 73% (243).322

106

The Bestmann-Ohira reaction was trialled for the conversion of aldehyde 177 to alkyne

179 using standard literature conditions (Scheme 3.38).319,320

TLC analysis showed that

treatment of aldehyde 177 with the BMO reagent formed a mixture of products.

Compound 254, isolated in 38% yield, was the major product formed, and the only

compound isolated after standard column chromatography on silica gel.

Scheme 3.38 Attempted Bestmann-Ohira reaction of aldehyde 177

Reagents and conditions: a) K2CO3 (2 eq), MeOH, 243 (1.2 eq), rt, 4 h, 38%.

Alkyne 254 was obtained as an oil. The molecular formula for 254 was C14H20O5, as

determined by HRMS (calc. for C14H20O5Na [M + Na]+ 291.1208, found 291.1202).

The IR spectrum showed a characteristic OH bond absorption band at 3444 cm-1

, a

terminal alkyne C-H band at 3282 cm-1

, and a carbon-carbon triple bond at 2112 cm-1

.

Detailed examination of the 1H NMR revealed signals for a terminal alkyne (s, δ =

2.46), a hydroxy group (s, δ = 4.75), four methoxy groups (4 ×s, δ = 3.25, 3.26, 3.32,

and 3.47), and 3 olefinic protons (δ = 5.77, 5.91, 6.11). The structure was determined

from detailed examination of 2D NMR spectra.

It was predicted that compound 254 was a result of three individual reaction steps. It

was likely that the terminal alkyne functionality was formed from the aldehyde group

via the proposed reaction mechanism outlined in Scheme 3.36. For the propargyl

alcohol portion of the molecule, it was assumed that residual methoxide ions attacked

the epoxide through a typical SN2 process at the least hindered epoxide carbon

providing a tertiary alcohol. The mechanism illustrated in Scheme 3.39 was proposed

for the formation of the methoxy alkene component of the molecule.

The carbonyl in 177 is an additional reactive site for the

dimethyldiazomethylphosphonate anion (244). It was assumed that the ketone reacted

via the mechanism described in Scheme 3.36 to give the vinylidene carbene 228

(Scheme 3.39). However, because the R groups in 258 are part of a ring system they are

107

believed to have a very low migratory aptitude, instead of 1,2 migration of the R

substituents, to the more strained 7-membered ring, it is assumed that the carbene

inserted into the excess methanol in solution to give the alkene 254 (Scheme 3.39).

Scheme 3.39. The proposed insertion mechanism of carbene 258 into methanol to give alkene 254.326

In an effort to prevent the epoxide from ring opening and to minimise the insertion side

reaction methanol was replaced with THF and one equivalent of n-BuLi (Scheme 3.40).

It was assumed that the n-BuLi would deacetylate the BMO reagent to produce the

reactive intermediate and be consumed before it could ring open the epoxide.

Unfortunately, the BMO reaction was still unsuccessful with these modified conditions.

All we observed was a complex mixture with no major isolable spots. It was also

doubtful that the modified conditions would have affected the selectivity of the carbonyl

addition by anion 244.

Scheme 3.40 Attempted modified Bestmann-Ohira reaction of aldehyde 177.

Reagents and conditions: a) n-BuLi (1 eq), THF, 243 (1.2 eq), rt, 4 h, 38%.

Pathway 2 - attempted Colvin rearrangement:

Chain extension of aldehyde 177 to alkyne 179 was also attempted using the Colvin

rearrangement (Scheme 3.41).327-329

The postulated mechanism for this reaction is

discussed in detail by Miwa et al.328

108

Scheme 3.41. Reagents and conditions: a) i) Diisopropyl amine (1.2 eq), n-BuLi (1.2 eq), THF,

259 (1.2 eq), 3 h ii) 1 M aq HCl, complex mixture.330

Thus, aldehyde 177 was treated with trimethylsilyldiazomethane 259 following standard

literature conditions to give a complex mixture (Scheme 3.41).327-329

It was presumed

that the lithiated silyl derivative was too reactive an intermediate for the electrophilic

substrate.

Pathway 3 - attempted homologation with phosphonium salt 260:

An alternative one-pot procedure comprising of a series of reactions beginning with a

Wittig olefination, with the ylide derived from diiodomethyltriphenylphosphonium

iodide (260), was also trialled for the conversion of aldehyde 177 to the terminal alkyne

179 (Scheme 3.42).331

The postulated mechanism for this reaction is discussed in detail

by Michel et al.331,332

Scheme 3.42. Reagents and conditions: a) 260 (1 eq), t-BuOK (2 eq), THF, -78°C, 30 min → t-BuLi

(1 eq), -78°C, 5 min → 37% w/w aq NH4Cl, -78°C to rt, 5 min, complex mixture.

Thus, aldehyde 177 was treated with the phosphonium salt 260 following standard

literature conditions (Scheme 3.42).331

Unfortunately, rather than forming the desired

alkyne 179, the reaction gave a complex mixture. It was likely the substrate was again

too sensitive to withstand the harsh conditions of the reaction.

109

Pathway 4 - homologation via the Corey-Fuchs protocol:

The Corey-Fuchs reaction refers to a two-step one carbon homologation method that

transforms an aldehyde into an alkyne.333,334

The proposed mechanism is illustrated in

Scheme 3.43. The first step in the reaction, also known as the Ramirez olefination,

refers to the conversion of an aldehyde to a dibromoalkene via a Wittig-like reaction

mechanism, bromotriphenylphosphonium bromide 262 is a by-product. The second step

involves the trans-elimination of HBr by a base, followed by lithiation and hydrolysis to

form the terminal alkyne. The lithium acetylide intermediate can also be treated with an

electrophile, prior to aqueous workup, to give a substituted alkyne.

Scheme 3.43. The proposed mechanism for the synthesis of terminal and substituted alkynes from

aldehydes via the Corey-Fuchs reaction protocol.334

Following a standard protocol for the Ramirez olefination, aldehyde 177 was added to a

mixture of PPh3 (4 eq) and CBr4 (2 eq) that had been stirring for 10 minutes in CH2Cl2

at 0°C.335

After 6 hours of stirring, TLC analysis showed that the starting material had

been consumed and that two new products had formed. After workup and purification

tetrabromide 272 and the desired dibromoalkene 178 were isolated in low yields of 30%

and 15% respectively (Scheme 3.44). Particularly diagnostic for the formation of 178

was the appearance of a resonance signal observed at δ = 6.96 ppm in the 1H NMR

110

which was assigned to the vinyl proton (-CH=CBr2). The structure of tetrabromide 272

was determined after careful analysis of 1H NMR,

13C NMR, 2D NMR, and HRMS

spectra.

Scheme 3.44. The Ramirez olefination of aldehyde 177.

Reagents and conditions: a) CBr4 (2 eq), PPh3 (4 eq), CH2Cl2, 0°C to rt, 6 h, 272 (30%), 178 (15%).

To our surprise, standard conditions for the Ramirez olefination in most Corey-Fuchs

procedures calls for the use of 2 equivalents of CBr4 with 4 equivalents of PPh3, this

seemed an excess. A literature search revealed that this is generally the case because

fewer equivalents of reagents leads to reduced yields and small amounts of unidentified

by-products.335

In our case however, the presence of excess reagents caused olefination

at both reactive carbonyl sites on substrate 177 as observed in the Bestmann-Ohira

reaction.

A literature search revealed that standard conditions for the Ramirez olefination suffers

from serious drawbacks when applied to sensitive and highly functionalised aldehyde

containing substrates.336

Substrates containing epoxides and other oxygenated

functional groups are particularly vulnerable because they are susceptible to attack by

the highly reactive electrophile PPh3Br2.336

We suspected that ketal 178 underwent de-

protection with the Lewis acidic by-product PPh3Br2 after the second olefination

reaction to give tetrabromide 272 via the mechanism proposed below (Scheme 3.45).

Scheme 3.45. The proposed mechanism for the de-protection of ketal 256 with PPh3Br2.

111

A modified procedure by Grandjean et. al. found that the addition of one equivalent of

NEt3 before the addition of the CBr4/PPh3 mixture suppresses side reactions by

quenching the electrophilic phosphonium salt.336

Given this new information, we

repeated the olefination but with Grandjean's modified procedure. Additionally, further

modifications were made to these conditions to try and further improve the yield of the

desired dibromoalkene 178. These results are summarised in Table 3.06.

Table 3.06. Ramirez olefination optimisation conditions

Entry CBr4 PPh3 NEt3 Concn Temp Time 273 178

1 2 eq 2 eq 1 eq 1.0 M -20 to -60°C 8 h - 40%

2 2 eq 2 eq 1 eq 1.0 M -20 to 20°C 18 h 23% 60%

3 2 eq 2 eq 1 eq 0.5 M -20 to -60°C 8 h 7% 25%

4 2 eq 2 eq 1 eq 0.5 M -20 to 20°C 8 h 53% 23%

5 1.2 eq 2.4 eq 1 eq 1.0 M -20 to 20°C 18 h 4% 43%

6 1.2 eq 2.4 eq 1 eq 0.5 M -20 to 20°C 18 h 31% 28%

The procedure developed by Grandjean et. al. was repeated without variation to give

solely the desired bromoalkene 178 at an improved yield of 40% (Entry 1, Table 3.06).

At this temperature, however, the reaction did not go to completion and a crude 1H

NMR showed the reaction to be a 50:50 mixture of starting material and product.

Additionally, the starting material could not be re-isolated after column chromatography

on silica gel.

In an attempt to push the reaction to completion, it was allowed to warm to room

temperature and stirred overnight (Entry 2, Table 3.06). The reaction went to

completion and the yield of the dibromoalkene 178 improved to 60%. Unfortunately, a

portion of the desired product also underwent di-olefination to give the tetrabromo

112

compound 273, in 23% yield. It appeared that the addition of NEt3 prevented de-

protection of the ketal functional group.

Considering that the reaction went selectively at -60°C to produce only the desired

compound, we thought that doubling the concentration of the reaction mixture at this

temperature might cause the reaction to go selectively and to completion (Entry 3,

Table 3.06). Unfortunately, the reaction still failed to go to completion and the

tetrabromo compound 273 and the dibromo compound 178 formed concurrently at this

increased concentration, both at lower yields of 7% and 25%, respectively. Warming the

reaction to room temperature, under the increased concentration (Entry 4, Table 3.06)

caused the reaction to go to completion. Unfortunately, a much higher yield of the

tetrabromo compound (53%) relative to the desired dibromo compound (only 23%) was

obtained.

Reducing the ratios of the CBr4 to 1.2 equivalents in an attempt to prevent the

tetrabromo product, only resulted in a mixture of both the products at lower yields

(Entries 5 and 6, Table 3.06). It appeared that olefination occurs concurrently at both

carbonyl groups without selectivity. The only exception to this rule was with the

conditions in entry 1 (Table 3.06).Unfortunately, the yield for this reaction was low and

the starting material could not be recovered making this an unviable option. Hence, the

yield of the Ramirez olefination could only be optimised to 60%.

With dibromoalkene 178 in hand we could explore various reactions to form the

terminal alkyne 179. Furthermore, we could also explore electrophilic trapping reactions

to try and extend the alkyne side chain to incorporate the isopropylene subunit observed

in the natural product.

In an attempt to synthesise the terminal alkyne 179 via a lithium-halogen exchange

reaction and trans-elimination of HBr, dibromoalkene 178 in THF at -78°C

was treated with 2.1 equivalents of n-BuLi. The resultant mixture was stirred for

30 minutes and then quenched with 37% w/w aq NH4Cl, as per standard literature

methods (reaction a, Scheme 3.46).337

A complex mixture resulted. It was assumed that

the substrate with its many reactive electrophilic sites, as discussed earlier, was too

sensitive to withstand the harsh base n-BuLi. The reaction was repeated with a shorter

reaction time of 10 minutes, but the outcome was the same (reaction b, Scheme 3.46).

113

Scheme 3.46. Reagents and conditions: a) n-BuLi (2.1 eq), THF, -78°C, 1.5 h → complex mixture;

b) t-BuLi (2.1 eq), THF, -78°C, 10 min→ inseparable mixture.

Considering t-BuLi is also a lithiating agent, but a less nucleophilic base than n-BuLi

due to its sterically hindered nature, we hoped that it would be a more effective reagent

for the lithium-halogen exchange reaction and trans-elimination of dibromoalkene 178

to alkyne 179. The conditions described above were repeated, but with 2.1 equivalents

of t-BuLi, and the reaction was stirred for 10 minutes. Unfortunately, the result was

again a complex mixture. It was clear that a milder and more selective base was

required for the elimination reaction.

A literature search revealed that for sensitive substrates, a clean trans-elimination

reaction with NaHMDS is considered to be a viable method to access bromo alkynes.336

Thus, bromoalkyne 275 was obtained in 45% yield after treating dibromoalkene 178

with 1.1 equivalents of NaHMDS in THF at -78°C (Scheme 3.47).

Scheme 3.47. Reagents and conditions: a) NaHMDS (1 eq), THF, -100°C, 10 min, 45%.

The starting material and product (178 and 275) have the same Rf (0.53 in 20:80

EtOAc/hexane) so it was not possible to carefully monitor the reaction by TLC,

fortunately the reaction went to completion after the literature specified amount of time

(10 minutes). Bromoalkyne 275 was a highly crystalline material and crystallised in

hexane to give fine, colourless crystals. A crystal structure, along with the 1H NMR,

13C

NMR, IR, and HRMS data for the isolated product, confirmed the structure to be 275

(Figure 3.08).

114

Figure 3.08. A single X-ray crystal structure ORTEP (50% probability) of bromo-alkyne 275.

The bromo-alkyne functional group is a synthetically versatile moiety. It can be

lithiated and quenched with various electrophiles for chain extension reactions or

quenched with mild acid to form simple terminal alkynes (equation 1, Scheme 3.48).

Additionally, a number of bromo-alkynes have been used in cross-coupling reactions

(equation 2, Scheme 3.48).338

Scheme 3.48. 1) The synthesis of terminal and substituted alkynes from an alkynyl bromide;

2) palladium-catalysed cross-coupling reaction of alkynyl bromide with an organoboronic acid.

Reagents and conditions: a) Pd2(dba)3, Cs2CO3, MeOH, rt.338

We were eager to see if treating our substrate with 1 instead of 2 equivalents of n- or t-

BuLi, would give us the favourable outcome of the terminal alkyne 179. Hence, bromo

alkyne 275 was dissolved in THF, cooled to -78°C and treated separately with n-BuLi

115

and t-BuLi, respectively (Scheme 3.49). After mild aqueous acidic workups with 37%

w/w aq NH4Cl, complex mixtures of several compounds were still obtained for both

reactions.

Scheme 3.49. Reagents and conditions: a) i) n-BuLi (1.1 eq), THF, -78°C, 30min ii) 37% w/w aq NH4Cl

→ complex mixture; b) i) t-BuLi (1.1 eq), THF, -78°C, 30min ii) 37% w/w aq NH4Cl → complex

mixture.

Alternatively, this two-step sequence can be performed in one pot. Thus, following

standard literature protocol, dibromoalkene 178 was dissolved in THF and cooled to

-78 C before the addition of 1.1 equivalents of NaHMDS to form the bromo alkyne in

situ. The subsequent mixture was stirred for 15 minutes at this same temperature before

the addition of 2 equivalents of t-BuLi. An extra equivalent of t-BuLi was required to

neutralise the HMDS proton which gets liberated in situ.336

After the resulting mixture

was stirred for a further 5 minutes, it was quenched with 37% w/w aq NH4Cl to give the

terminal alkyne 179 in 28% yield (Scheme 3.50). It was surprising that the one-pot

procedure worked successfully to give the terminal alkyne 179, but the reactions when

performed separately did not work.

Scheme 3.50. Reagents and conditions: a) i) NaHMDS (1 eq), t-BuLi (2 eq), THF, -100°C, 20 min

ii) 37% w/w aq NH4Cl, -100°C to rt, 5 min, 28%.

Particularly diagnostic for the formation of 179 was the appearance of a resonance

signal observed at δ = 2.56 ppm in the 1H NMR, which was assigned to the terminal

alkyne proton.

116

3.2.10 The attempted synthesis of SDEF 678 (138) via tertiary alcohol 280

Given that the terminal alkyne 179 could be synthesised from the dibromoalkene 178 in

one step, we thought it pertinent to examine if electrophilic trapping could be utilised to

extend the alkyne side chain to include the isopropylene sub-unit observed in the natural

product 138. Thus, a three-step procedure starting from the dibromo alkene 178 to

SDEF 678 (138) was devised (Scheme 3.51).

Scheme 3.51. Proposed synthesis of SDEF 678 (138) from dibromoalkene 178.

Reagents and conditions: a) i) NaHMDS (1 eq), t-BuLi (2 eq), THF, -100°C, 20 min ii) acetone (5 eq),

5 min, -100°C, 5 min, rt, 37% w/w aq NH4Cl.

We planned to synthesise the tertiary alcohol 280 by treating the lithiated acetylide

intermediate with acetone to undergo a simple 1,2 addition reaction at the carbonyl

group in order to form a tertiary alkoxy anion. An aqueous acidic workup was to give us

the tertiary alcohol 280. Then, following a diastereoselective reduction using DIBAL-

H308

we had planned to dehydrate the ketone to the alkene and de-protect the ketal to the

ketone, in the same acidic step, to give the natural product 138. Unfortunately, the first

step in this sequence did not proceed the way we intended.

Dibromoalkene 178 was dissolved in THF and cooled to -100°C before the

addition of 1.1 equivalents of NaHMDS to form the bromo alkyne 275 in situ. The

subsequent mixture was stirred for 20 minutes at this same temperature before

117

the addition of 2 equivalents of t-BuLi. The resulting mixture was then stirred for a

further 10 minutes before it was quenched with acetone and exposed to an acidic

aqueous workup. Purification via standard column chromatography gave the terminal

alkyne 179 (38%), and 4-hydroxy-4-methylpentan-2-one (179a) (Scheme 3.52).

4-Hydroxy-4-methylpentan-2-one (179a) occurs as the product of an aldol addition

between acetone and a base.

Scheme 3.52. Reagents and conditions: a) i) NaHMDS (1 eq), t-BuLi (2 eq), THF, -100°C, 20 min

ii) acetone (5 eq), 5 min, -100°C, 5 min, rt, 37% w/w aq NH4Cl, 179 (38%).

3.2.11 The attempted synthesis of SDEF 678 (138) via alcohol 199

We felt we could improve the overall yield of terminal alkyne 179. Thus, a new

synthetic strategy was devised which aimed to reduce the carbonyl group of epoxide

176 diastereoselectivity using DIBAL-H to give the diol 199. Subsequent oxidation of

the primary alcohol group in 199 was to then give aldehyde 284

(Scheme 3.53). This was to be followed by a series of reactions that would eventually

give terminal alkyne 179. We were optimistic that we could improve the overall

reaction yield of the terminal alkyne (179) once the ketone was reduced and no longer a

second reactive electrophilic site. Thus, epoxide 176 was treated with DIBAL-H, under

standard literature conditions (Scheme 3.53).270,308

Unfortunately, instead of the desired

diol 199 the reaction gave a mixture of highly polar and inseparable products.

118

Scheme 3.53. Proposed optimisation of Corey-Fuchs reaction through epoxide intermediate 199.

Reagents and conditions: a) i) DIBAL-H (2 eq), THF, -78°C, 30 min ii) 63% w/w aq KNaC4H4O6.4H2O.

Given that the carbonyl group could not be reduced before the Ramirez olefination, we

thought that it might be possible to improve the yield of the trans-elimination, lithiation,

and hydrolysis steps to give terminal alkyne 179 by reducing the carbonyl group after

the olefination reaction. Hence, dibromoalkene 178 was treated with DIBAL-H

(2 equivalents), under standard literature conditions to give a mixture of the

diastereoisomers 285 and 286 (88% yield), in a ratio of 10:1, as determined by 1H NMR

(Scheme 3.54).

Scheme 3.54. Reagents and conditions: a) i) DIBAL-H (2 eq), THF, -78°C, 1 h ii) 63% w/w aq

KNaC4H4O6.4H2O, 285 (80%), 286 (8%).

The reduction of a cyclohexenone epoxide with DIBAL-H, to establish a hydroxyl

group at C2 in a trans-position to the established epoxide, is a widely used

diastereoselective reduction method.308

It is assumed that the diastereoselectivity of the

reaction is controlled by the direct coordination of DIBAL-H to the epoxide oxygen

119

which results in intramolecular hydride delivery syn to the epoxide resulting in an anti-

configured hydroxy product as the favoured isomer (Figure 3.08).308

Figure 3.08. Proposed intermediate for the diastereoselective synthesis of alcohol 285 from

ketone 178.308

The diastereoisomers 285 and 286, as a mixture of isomers, could not be separated via

standard column chromatography as they had the same Rf (0.62 in 50:50 EtOAc/hexane)

on silica and alumina gel. Additionally, column chromatography on silica gel caused the

products to decompose. Fortunately, the reaction was very clean. The diastereoisomers

were isolated after a quick workup, and no further purification was required.

Particularly diagnostic for the formation of 285 were the appearance of resonance

signals observed at δ = 4.43-4.39 (multiplet) and 3.44 ppm in the 1H NMR, which were

assigned to the proton at H-2 and the hydroxyl group, respectively.

Following the conditions described earlier, alcohols 285 and 286 were treated with

various bases and electrophiles in an attempt to synthesise a variety of alkyne functional

groups (Scheme 3.55). An extra equivalent of base was added in all cases to counteract

the equivalent of base that would be consumed to de-protonate the alcohol.336

Unfortunately, the unprotected alcohol was too reactive an intermediate to withstand the

described conditions and in all cases (reactions 1-3, Scheme 3.55) a complex mixture

was obtained.

120

Scheme 3.55. Reagents and conditions: a) NaHMDS (2 eq), THF, -100°C, 10 min, complex mixture;

b) NaHMDS (1 eq), t-BuLi (3 eq), THF, -100°C, 20 min, complex mixture; c) i) NaHMDS (1 eq), t-BuLi

(3 eq), THF, -100°C, 20 min ii) acetone (5 eq), 5 min, -100°C, 5 min, rt, 37% w/w aq NH4Cl, complex

mixture.

It was clear that additional steps would be required to protect the free alcohol in 285 if it

was to withstand the harsh reagents required for trans-elimination and lithiation. The

TBDMS ether was chosen as a protecting group due to its mild protecting conditions,

chemoselective removal, and because it has excellent stability towards strong bases.

Thus, secondary alcohols 285 and 286 were treated with TBDMSCl in the presence of

imidazole and a catalytic amount of DMAP, under standard literature conditions, to give

the protected alcohol 289 (Scheme 3.56).339

Scheme 3.56. Reagents and conditions: a) TBDMSCl (1.2 eq), imidazole (2.5 eq), DMF, rt, 3 h, 52%.

121

The protected diastereoisomer 289 was isolated as the major product (52% yield) after

purification via standard column chromatography on silica gel. Unfortunately, what we

suspected was the other protected diastereoisomer could not be isolated purely as it

eluted with a mixture of other compounds at the beginning of the column. Particularly

diagnostic for the formation of 289 were the appearance of resonance signals observed

in the 1H NMR and

13C NNMR spectra that were assigned to signals corresponding to

the TBDMS group (δ = 0.88 SiC(CH3)3, 0.13 SiCH3, 0.11 SiCH3, 25.8 SiC(CH3)3, 18.1

SiC(CH3)3, -4.4 SiCH3, -4.6 SiCH3).

The yield of the reaction was much lower than expected for a standard TBDMS

protection. A Study by Weinreb et al.340

revealed that epoxy allylic alcohols such as 285

can react with HCl (a by-product of the reaction) to undergo acid-catalysed nucleophilic

ring opening reactions to give chloro alcohols (Scheme 3.57). No chloro alcohol was

isolated, but considering that the protected alcohol 289, was the major product isolated

from a complex mixture, it was a possibility.

Scheme 3.57. Reagents and conditions: a) TBDMSCl (1.5 eq), imidazole (2.7 eq), DMF, 0°C to rt.340

Attempts to optimise the protection of secondary alcohol 285 were unsuccessful despite

making changes to the reaction temperature, substrate concentration, mixture of

solvents, base additives, and even the protecting agent (Table 3.07). The highest yield

that could be obtained for the protected alcohol was 52%. Protection with a MEM group

was also attempted, unfortunately without success. The results for the protecting group

installation reactions are summarised in Table 3.07.

122

Table 3.07. Optimisation reactions for the protection of alcohol 283

Reagents and conditions: RCl, base, solvent, catalyst, temp, time.

Entry RCl Base Solvent Catalyst Temp Time 293

1 TBDMSCl

2 eq

Imidazole

5 eq DMF - rt 2 h 52%

2 TBDMSCl

2 eq

Imidazole

5 eq THF

DMAP

10 mol% 0°C to rt 30 min 10%

3 TBDMSCl

1.2 eq

Imidazole

5 eq THF - 0°C to rt 3 h 46%

4 TBDMSCl

1.2 eq

Hunig's

2.4 eq THF - 0°C to rt 1 h 50%

5 MEMCl

1.2 eq

Hunig's

2.4 eq CH2Cl2 0°C 30 min CM

6 MEMCl

1.2 eq

NaH

2.4 eq THF 0°C 30 min CM

CM = complex mixture.

The synthesis was continued with the TBDMS protected dibromo alkene 289, which

was exposed to trans-elimination conditions with NaHMDS to give bromo alkyne 295

in 79% yield (Scheme 3.58). As predicted, the yield for the elimination reaction with

NaHMDS was considerably higher when the carbonyl group at C2 was masked, the

yield of the elimination reaction increased from 45% (Scheme 3.47) to 79%

(Scheme 3.58).

Scheme 3.58. Reagents and conditions: a) NaHMDS (2 eq), THF, -100°C, 10 min, 79%; b) i) NaHMDS

(1 eq), t-BuLi (2 eq), THF, -100°C, 20 min ii) acetone (5 eq), 5 min, rt, 37% w/w aq NH4Cl.

123

TBDMS protected bromo-alkyne 295 was then dissolved in THF, cooled to -78°C,

treated with t-BuLi to form a lithiated acetylide, and quenched with acetone and

acidified with 37% w/w aq NH4Cl. A 1H NMR of the crude reaction mixture indicated

the synthesis of tertiary alcohol 296. Resonance signals in the crude 1H NMR were

assigned to key structural features as follows: δ = 5.76 (ddd, 1H, CH=CH-6), 5.54 (dd,

1H, CH=CH-1), 4.40 (dt, , H-5), 3.56 (s, 3H, OCH3), 3.40 (dd, 1H, H-4), 3.33 (s, 3H,

OCH3), 1.53 (s, 6H, C(CH3)2OH), 0.89 (s, 9H, C(CH3)3), 0.13 (s, 3H, SiCH3), 0.12 (s,

3H, SiCH3). Unfortunately, the tertiary alcohol could not be re-isolated after it was

subjected to purification via column chromatography on silica gel. Propargyl alcohols

are especially acid sensitive and it is possible that the product underwent acid-catalysed

hydrolysis on the column. Additionally, the reaction outcome could not be reproduced.

Reducing the carbonyl group and protecting the free alcohol did not improve the overall

yield or efficiency of the synthetic sequence. The TBDMS protected bromo alkyne 295

was synthesised in three-steps starting from dibromoalkene 178 in an overall yield of

35%. In contrast, its unprotected counterpart bromo alkyne 275 was synthesised in one-

step from dibromo alkene 178 in 45% yield (Scheme 3.47).

3.2.12 The synthesis of SDEF 678 (138) from terminal alkyne 179

At this stage in the synthesis, we had intended to proceed using the terminal alkyne 179

as a key intermediate. We had planned to expose 179 to standard Sonogashira reaction

conditions with 2-bromoprop-1-ene 297 to generate isopropylene alkyne 180; then to

reduce 180 diastereoselectively with DIBAL-H to give secondary alcohol 181; and

finally to de-protect 181 under acidic conditions to give SDEF 678 (138)

(Scheme 3.59).

124

Scheme 3.59. Reagents and conditions: a) 297 (5 eq), PdCl2(PPh3)2 (25 mol%), CuI (25 mol%), Hunig's

base (10 eq), THF, sealed tube, rt, 18 h; b) i) DIBAL-H (2 eq), THF, -78°C, 1 h ii) 63% w/w aq

KNaC4H4O6.4H2O; c) AcOH, THF/acetone/H2O (1:1:1), 0°C.

However, we did not proceed with this synthetic plan because we felt that it was

necessary to investigate a more efficient method to incorporate the alkyne side chain for

SDEF 678 and speciosins A-F. Also, the synthesis of alkyne 179 had a low overall yield

of 8% over 5 steps. We wanted to access the acetylene side chains of speciosins A-F

(139-144) via a more efficient method than a potential four-step synthesis developed

from allylic alcohol 172. Thus, at this stage we changed synthetic directions. However,

taking into consideration the enantioselectivity of the epoxidation step (72% ee), we

intended to revisit this synthetic strategy at a later date if a more efficient and

stereoselective alternative synthesis could not be developed.

125

3.3 The formal synthesis of SDEF 678 (138)

Our first synthetic approach to SDEF 678 (138) avoided the use of a Diels-Alder/retro-

Diels-Alder protecting group strategy because of the low yield associated with the

reverse Diels-Alder reaction. However, it was clear from our initial synthesis that not

protecting one of the benzoquinone ketal alkenes limits the efficiency and scope of the

epoxidation reaction, hinders the ability to mask the carbonyl group and also means that

the alkyne must be built up in several steps instead of inserted in one efficient step.

Thus, a new synthetic plan in which the less substituted benzoquinone ketal alkene was

protected as a Diels-Alder adduct was devised (Scheme 3.60).

Scheme 3.60. Retrosynthetic analysis of SDEF 678 (138) via key intermediate ketal 173.

The key steps in the reaction sequence involved a palladium-catalysed Sonogashira

reaction to insert the alkyne side chain; a Diels-Alder reaction to block of the less-

substituted alkene; a stereoselective nucleophilic epoxidation to insert the epoxide; a

reverse Diels-Alder reaction to regenerate the free alkene; a stereoselective DIBAL-H

reduction; and a ketal de-protection to give the natural product. Our first step was to

find the most efficient route to key intermediate ketal 173.

126

3.3.1 The attempted synthesis of ketal 173

Pathway 1:

As outlined in Scheme 3.61 the synthetic strategy envisioned for pathway 1 relied on

the implementation of a number of key transformations to synthesise ketal 173. A one

carbon homologation method would be used to obtain 3-ethynylphenol (299), followed

by a phenolic oxidation with PIDA to produce the key ethynyl benzoquinone ketal core

observed in 300. A Sonogashira reaction would then be employed to attach the

isopropylene side chain to construct the target ketal 173.

Scheme 3.61. Proposed synthesis of ketal 332.

Reagents and conditions: a) i) Diisopropyl amine (2 eq), n-BuLi (2 eq), THF, 259 (1 eq), 3 h ii) 1 M aq

HCl, 67%; b) PhI(OAc)2 (1.1 eq), MeOH, 0°C to rt, 3 h, decomposition.

The synthesis commenced with 3-hydroxybenzaldehyde (181) which was converted to

3-ethynylphenol (299) in 67% yield via a Colvin rearrangement.327-329

The synthesis of

ethynyl benzoquinone ketal 300 was then initiated by oxidation of the phenol 299 with

PIDA. However, the crude product decomposed when exposed to column

chromatography on silica gel. Thus, pathway 1 was not investigated further and

alternative routes to ketal 173 were examined.

127

Pathway 2:

The synthetic strategy envisioned for pathway 2 relied on a palladium-catalysed

Sonogashira reaction with bromo benzoquinone ketal 301 as the key transformation to

synthesise ketal 173 (Scheme 3.62). Our first step was to find the most efficient route to

synthesise bromo benzoquinone ketal 301.

Scheme 3.62. Retrosynthetic analysis of ketal 173 via key intermediate 3-Bromo-4,4-

dimethoxycyclohexa-2,5-dien-1-one (301).

The first test route began with 3-bromophenol which was oxidised with PIDA to give

bromo benzoquinone ketal 301 in 31% yield (Scheme 3.63). The low yield for the

desired ketal 301 in this preliminary investigation led us to explore higher yielding

alternative methods.

Scheme 3.63. Reagents and conditions: a) i) PhI(OAc)2 (2.1 eq), MeOH, 0°C to rt, 3 h ii) 9% w/w aq

NaHCO3, 5 min, 31%.

The second route to ketal 301 began with commercially available 4-methoxyphenyl

acetate (302) which was brominated using literature conditions to give acetoxy

bromobenzene 303 in 90% yield (Scheme 3.64).341

Base hydrolysis of acetoxy

compound 303 then gave the bromo phenol 304 in 98% yield.341

This was followed by

phenolic oxidation of 304 with PIDA to give bromo benzoquinone ketal 301 in 71%

yield. Thus, bromo benzoquinone ketal 301 was synthesised in 3 steps from a

commercially available precursor in 63% overall yield (Scheme 3.64). We proceeded

with this higher yielding second route for the synthesis of bromo benzoquinone ketal

301.

128

Scheme 3.64. Reagents and conditions: a) Br2 (1.2 eq), NaOAc (1.9 eq), AcOH, rt, 18 h, 90%;342

b) LiOH (1.1 eq), MeOH/H2O (8:1), rt, 30 min ii) 1 M aq HCl, 98%; c) i) PhI(OAc)2 (1.1 eq), MeOH,

0°C to rt, 3 h ii) 9% w/w aq NaHCO3, 5 min, 71%.

After the synthesis of bromo benzoquinone ketal 301, our first objective was to find

optimal conditions for its coupling with terminal acetylene 2-methylbut-1-en-3-yne

(305) via the Sonogashira protocol (Scheme 3.65). Unfortunately, the attempted

Sonogashira reactions failed to give adequate amounts of the desired product 173. The

highest yielding conditions only produced the desired ketal 173 in 4% yield

(Scheme 3.65). The major product of the reaction was instead phenol 306 (36% yield)

(Scheme 3.65). Phenol 306 and ketal 173 were stored for later use as natural product

138 derivatives, for future biological testing.

Scheme 3.65. Reagents and conditions: a) PdCl2(PPh3)2 (6 mol%), CuI (12 mol%), 305 (1 eq), NEt3

(1 eq), DMF, 60°C, 3 h, 306 (36%), 173 (4%).

Thus, a Sonogashira cross-coupling reaction between bromo benzoquinone ketal 301

and alkyne 305 was determined as an inefficient method to synthesise ketal 173 and

pathway 2 was not investigated further. Alternative routes to ketal 173 were examined.

Pathway 3:

Our third synthetic strategy towards the synthesis of ketal 173 commenced with the

conversion of bromobenzene 303 to alkyne 308 in nearly quantitative yield (94%) with

2-methylbut-3-yn-2-ol (307) under Sonogashira cross-coupling conditions using

129

catalytic PdCl2(PPh3)2 (Scheme 3.66). Coupling with 2-methylbut-3-yn-2-ol (307),

followed by dehydration to the isopropylene intermediate 306, was preferred to the

direct coupling of 303 with 2-methylbut-1-en-3-yne (305) because of the high volatility

and high cost of the enyne 305.

Scheme 3.66. Reagents and conditions: a) PdCl2(PPh3)2 (2 mol%), CuI (6 mol%), 307 (1 eq), NEt3 (1 eq),

CH3CN, reflux, 16 h, 94%; b) i) TsOH (5 mol%), toluene , 60°C, 3 h, 60% ii) LiOH (2.5 eq), MeOH/H2O

(8:1), 60°C, 30 min, 98% (overall 78%); c) PhI(OAc)2 (1.1 eq), MeOH, 0°C to rt, 43%.

With the propargyl alcohol 308 in hand, the dehydration and deprotection reactions to

the enyne phenol 306 were accomplished in two steps and 78% overall yield

(Scheme 3.67). The dehydration reaction in anhydrous toluene, in the presence of p-

toluenesulfonic acid (5 mol%), gave a mixture of the protected and de-protected

dehydration products phenyl acetate 308 and phenol 306 in 20% and 60% yields,

respectively (Scheme 3.67). The temperature, catalyst loading and reaction time were

crucial in this step. At temperatures higher than 60°C, a catalyst loading above 5 mol%,

or after more than 3 hours stirring, complex mixtures were obtained.

130

Scheme 3.67. Reagents and conditions: a) p-TsOH (5 mol%), toluene, 60°C, 3 h, 309 (20%), 306 (60%).

Alkynes 309 and 306 were easy to separate and identify but were used as a crude

mixture for base hydrolysis in future scale-up reactions. Base hydrolysis of the mixture

gave the enyne phenol 306 in 98% yield (Scheme 3.66). Finally, the requisite ketal

starting material 173 was obtained via the oxidation of phenol 306 using PIDA in

methanol. TLC analysis showed that the enyne 173 was formed from phenol 306 nearly

quantitatively. Despite this, enone 173 was only isolated in 43% yield after silica gel

chromatography (Scheme 3.66).

3.3.2 The attempted synthesis of epoxide 180

Investigations by Shi et al.343-345

had shown a highly enantioselective method for the

epoxidation of trans- and tri-substituted olefins using a fructose-derived ketone (310) as

a catalyst, and OxoneTM

as an oxidant.* In addition, the group had found the epoxidation

to be chemoselective for conjugated enynes.347

The epoxidation proceeds via an

electrophilic dioxirane intermediate method and is less effective for cis- and terminal

olefins compared to trans- and tri-substituted olefins. Thus, we were hopeful that

treating ketal 173 with the Shi epoxidation conditions would give epoxide 180

(Scheme 3.68).

Scheme 3.68. Reagents and conditions: a) Na2B4O7 (1 eq) in 0.04 M aq Na2(EDTA), Bu4NHSO4

(7 mol%), 310 (1 eq), Oxone (4 eq) in 0.04 M aq Na2(EDTA), K2CO3 (8 eq) in H2O, 0°C, 1.5 h, 94%.

* The fructose derived Shi-catalyst 310 was synthesised in two steps from inexpensive D-fructose via

ketalisation followed by oxidation (Scheme 3.69).346

Scheme 3.69. Reactions and conditions: a) H2SO4 (1 eq), acetone, rt, 2.5 h, 78%; b) DMP (2.5 eq), CH2Cl2, rt, 8 h, 87%.346

131

Thus, enyne 173 was treated with chiral ketone 310 and OxoneTM

in the presence of

K2CO3, Na2B4O7, Na2(EDTA), and Bu4NHSO4 under standard Shi epoxidation

conditions (Scheme 3.68).343,344

However, instead of producing the desired epoxide

180, epoxidation occurred at the least hindered terminal alkene to give epoxide 311 in

94% yield. Considering the oxidising agent is electrophilic and the terminal alkene was

the more electron-rich of the pair, this result was not surprising. In the future, we intend

to determine the outcome of the reaction using tertiary alcohol 314 as a substrate

(Scheme 3.70).

Scheme 3.70. Reagents and conditions: a) Na2B4O7 (1 eq) in 0.04 M aq Na2(EDTA), Bu4NHSO4

(7 mol%), 310 (1 eq), Oxone (4 eq) in 0.04 M aq Na2(EDTA), K2CO3 (8 eq) in H2O, 0°C.

3.3.3 The Taylor synthesis of SDEF 678 (138) and speciosins A-F (139-144)

At this stage, due to the unsuccessful epoxidation of ketal 173, we were prepared to

investigate the Diels-Alder reaction to block off the less hindered alkene of ketal 173.

However, during our attempted synthesis of Diels-Alder adduct 174 it came to our

attention that the group of Taylor et al.258

had published the synthesis of SDEF 678

(138) and the speciosin metabolites 139-144 via a synthetic route based around a similar

Diels-Alder/retro-Diels-Alder approach. Their synthesis of SDEF 678 (138) also used

ketal 173 as a key intermediate (Scheme 3.71).

132

Scheme 3.71. Taylor's synthesis of SDEF 678 (138).258

Reagents and conditions: a) PhI(OAc)2 (2.1 eq), MeOH, 0°C to rt, 3 h, 56%;348

b) 318 (1 eq),

trans-PdBr(N-succ)(PPh3)2 (5 mol%), THF, rt, 98%; c) 319 (20 mol%), cyclopentadiene (5 eq), CH2Cl2,

-78°C, 87%; d) AcOH, THF/acetone/H2O (1:1:1), 0°C, 83%; e) H2O2, DBU, MeCN, -20°C, 92%

(anti:syn = 64:36); f ) Ph2O, 250°C, 45%.258

In the reaction sequence by Taylor et al.258

the less substituted alkene on ketal 173 was

protected via a Diels-Alder reaction. This was achieved using Corey's chiral

oxazaborolidine/triflic acid adduct giving a racemic mixture of exclusively the endo

adduct 174 in 87% yield. The diastereoselectivity of the endo adduct was then used to

direct a stereoselective epoxidation of enone 174 and a reduction under Luche

conditions to give 320 in 98% yield. Exposure of ketal 320 to mildly acidic de-

protection conditions then gave enone 321. Nucleophilic epoxidation of enone 321

using hydrogen peroxide and DBU in acetonitrile then gave a diastereoselective mixture

of epoxides. The major isomer was the anti-epoxide in 59% yield (298), the syn-epoxide

133

was formed in 33% yield. Finally, the retro-Diels-Alder reaction of 298 in diphenyl

ether at 250°C gave SDEF 678 (138) in 80% yield, based on recovered starting material

(45% isolated yield).258

Thus, natural product 138 was synthesised as a racemic mix in 7

steps and 16% overall yield. In addition, the synthetic methodology was easily applied

to prepare the speciosins B and C (139 and 140).258

The synthetic sequence developed

by Taylor et al. is concise and applicable to the syntheses of SDEF 678 derivatives,

however it is not enantioselective.

3.3.4 The formal synthesis of SDEF 678 (138)

Considering Taylor et al. synthesised racemic SDEF 678 (138) from ketal 173,258

we

had a non-enantioselective formal synthesis of 138 commencing from 4-methoxyphenyl

acetate 302 in 9 steps and 8% overall yield (Scheme 3.72).

Scheme 3.72. Formal synthesis of SDEF 678 (138).

Reagents and conditions: a) Br2 (1.2 eq), NaOAc (1.9 eq), AcOH, rt, 18 h, 90%; b) PdCl2(PPh3)2

(2 mol%), CuI (6 mol%), 307 (1 eq), NEt3 (1 eq), CH3CN, reflux, 16 h, 94%; c) i) TsOH (5 mol%),

toluene, 60°C, 3 h, 60% ii) LiOH (2.5 eq), MeOH/H2O (8:1), 60°C, 30 min, 98% (overall 78%);

d) PhI(OAc)2 (1.1 eq), MeOH, 0°C to rt, 43%.

134

135


In summary, we have achieved a non-enantioselective formal synthesis of SDEF 678

(138), in 9 steps and 8% overall yield, starting from 4-methoxyphenyl acetate (302), and

incorporating work by Taylor et al. (Scheme 3.72).258

Compared to Taylor's synthesis,

our formal synthesis has two extra steps and an 8% lower yield. However, our synthesis

also uses cheaper starting materials and no toxic tin reagents. Additionally, we feel that

the yield of our phenolic oxidation step could be improved from 43% yield in the future

by treating the silica gel with base before purification of 173 with column

chromatography.

In addition to the formal synthesis of SDEF 678 (138), we have also developed an

enantioselective approach to the synthesis of terminal alkyne 179 in 5 steps and 8%

overall yield (Scheme 3.74).

Scheme 3.74. The enantioselective synthesis of alkyne 179.

Reagents and conditions: a) PhI(OAc)2 (2.1 eq), MeOH, 0°C to rt, 3 h ii) 9% w/w aq NaHCO3, 2 min,

concentrated in vacuo, 65%; b) Ti(O-iPr)4 (1 eq), (+)-DIT (1.2 eq), CH2Cl2, t-BHP (2 eq), -20°C to rt,

18 h, workup C, 44% (83% conversion yield); c) IBX (3 eq), EtOAc, 18 h, 85%; d) CBr4 (2 eq), PPh3

(2 eq), NEt3 (1 eq), CH2Cl2, -20°C to rt, 18 h, 60%; e) i) NaHMDS (1.1 eq), t-BuLi (2.1 eq), -78°C, 5 min

ii) 37% w/w aq NH4Cl, 28%.

Current work in our group is focused on the enantioselective total synthesis of SDEF

678 (138) and speciosins A-F (139-144) using enantiopure 179 as a key intermediate

(Scheme 3.59 and Scheme 3.75). We plan to use synthesised samples of natural

136

products 138-144 for future biological evaluation studies against Gaeumannomyces

graminis var. tritici (Ggt) and other phytopathogens.

Scheme 3.75. Reagents and conditions: a) 297a (5 eq), PdCl2(PPh3)2 (25 mol%), CuI (25 mol%), Hunig's

base (10 eq), THF, sealed tube, rt, 18 h; b) i) DIBAL-H (2 eq), THF, -78°C, 1 h ii) 63% w/w aq

KNaC4H4O6.4H2O; c) AcOH, THF/acetone/H2O (1:1:1), 0°C; d) DMDO, Me2CO, rt;258

e) NaBH4 (1 eq),

CeCl3.7H2O (1.2 eq), MeOH, 0°C.

137

Chapter 4

Studies into the Total Syntheses of Glaciapyrroles B and C

138

139

4.1 Introduction

4.1.1 An introduction to glaciapyrroles B and C

In 2004, the group of Potts et al. detailed the isolation and structural determination

of two new pyrrolosesquiterpenes named glaciapyrroles B (322) and C (323)

(Figure 4.01).6 Natural products 322 and 323 are metabolites produced by Streptomyces

sp. (NPS008187), a Nereus strain isolated from a marine sediment collected in Alaska.6

Glaciapyrroles B (322) and C (323) were identified using a chemical profiling method

referred to as analytical high performance liquid chromatography with photodiode array

(HPLC-PDA).6 This approach results in rapid analysis of crude extracts and can

improve the identification process of new chemical entities via comparison of an

extract's UV spectrum against an in-house spectroscopic library of known products.

Using this approach, compounds 322 and 323 were determined as novel and their

structures were established using a number of spectroscopic methods. The absolute and

relative stereochemistries of 322 and 323, however, are yet to be determined.

Figure 4.01. Glaciapyrroles B (322) and C (323) are pyrrolosesquiterpenes, produced from the Nereus

strain Streptomyces sp. (NPS008187). The key retrosynthetic disconnection of the C(sp2)- C(sp

2) bond

between C8 and C9 is highlighted in red.6

To date, the cytotoxicities of glaciapyrroles B and C have not been determined to see if

they have potential antitumour activity. However, a related structure, glaciapyrrole A

(Figure 4.02), was shown to have potential antitumour activity because it inhibited both

colorectal adenocarcinoma HT-29 and melanoma B16-F10 tumour cell growth with an

IC50 value of 180 μM.6

140

Figure 4.02. Glaciapyrrole A (324) a pyrrolosesquiterpene produced from the Nereus strain Streptomyces

sp. (NPS008187).6


Given that there has been no published synthetic or biological work for either

glaciapyrrole B (322) or glaciapyrrole C (323) to date, our aim was to develop concise

total syntheses for both natural products for use in future biological assays. Our efforts

towards total syntheses relied heavily on exploitation of a key disconnection at the

central C(sp2)-C(sp

2) bond between C8 and C9 (Figure 4.01). It was hypothesized that

various palladium-catalysed cross-coupling processes (e.g. the Heck, Suzuki, and

Sonogashira reactions, the last one indirectly) could be used to establish this connection.

Also, given that epoxides and diols are inter-convertible we aimed to synthesise either

glaciapyrrole B or glaciapyrrole C, and then access the other natural product through the

appropriate epoxide ring opening or ring closing reaction as required.

141

4.2 The attempted synthesis of glaciapyrrole C (323) via a key Heck

cross-coupling reaction

Our first synthetic approach to glaciapyrrole C attempted to take advantage of an

intermolecular Heck cross-coupling reaction to establish the C-(sp2)-C(sp

2) bond

between C8 and C9. There were two potential Heck cross-coupling pathways,

depending on the choice of disconnection fragments as illustrated in Scheme 4.01.

Scheme 4.01. Retrosynthetic disconnection showing a Heck cross-coupling reaction as the key step.

The first set of coupling fragments included an electron-rich alkene 326 as the olefin

coupling partner, and a vinyl iodide 327 as the electrophilic coupling partner. We

decided against the use of these fragments as precursors for several reasons. To begin

with, allylic epoxides such as 326 are reactive substrates in the Tsuji-Trost reaction.50

They interact with Pd(0) complexes to form reactive -allyl species (such as 330) that

undergo nucleophilic addition (Scheme 4.02).349-351

We were concerned that a -allyl

intermediate would form between 326 and our active Pd(0) catalytic species to give by-

products.

142

Scheme 4.02. The formation of a -allyl intermediate.349-351

Additionally, terminal alkenes with electron-donating groups, such as 326, are generally

not suitable substrates for the Heck reaction because they normally lead to a mixture of

regioisomers, double bond isomers, and mixtures of cis- and trans-isomers under

traditional Heck cross-coupling conditions (Scheme 4.03).50

Scheme 4.03. The potential products from the use of an electron-rich olefin in the Heck reaction.50

It was thought we might have more success with the second series of cross-coupling

partners 328 and 329. Olefin 328 is substituted with an electron-withdrawing group and

similar substrates are generally reactive when exposed to standard Heck cross-coupling

reaction conditions because electronic effects direct vinylation to the most electron

deficient carbon beta to the electron withdrawing group.50

However, olefins that react

smoothly in Heck reactions are generally terminal alkenes.50

It was unsure what

stereochemistry the products of a 1,2-disubstituted olefin (such as 329) would possess,

but we thought the reaction was worth attempting. Thus, we begun our investigations

with the synthesis of coupling partners 328 and 329.

4.2.1 The Synthesis of acrylate 329

The first step in the synthetic sequence was to synthesise the acrylate coupling partner

329. The preparation of compound 329 had been reported previously in the literature

starting from pyrrole 331.352

These conditions were repeated to give acrylate 329 in 2

steps and 62% overall yield (Scheme 4.04).

143

Scheme 4.04. Reagents and conditions: a) NaH (1.1 eq), THF, p-TsCl (1 eq), rt, 3.5 h, 96%;

b) 333 (4 eq), TFAA (1.5 eq), CH2Cl2, rt, 6 h, 65%.352

To begin, N-tosyl-protected pyrrole 332* was synthesised in 96% yield after

treatment of freshly distilled pyrrole (331) with sodium hydride and toluenesulfonyl

chloride (Scheme 4.04). This was followed by the treatment of 332 with crotonic

acid (333), in the presence of trifluoroacetic anhydride, to give the acrylate derivative

329 in 65% yield after a regio-specific α-acylation of the pyrrole derivative 332

(Scheme 4.04).352,354

The spectroscopic data for 329 matched that reported previously in

the literature.352

With the acrylate 329 in hand we turned our attention to the synthesis

of the vinyl halide coupling partner.

4.2.2 The attempted synthesis of vinyl iodide 337

It is commonly known that aldehydes are a common precursor to vinyl halides. Thus,

our first step was to synthesise aldehyde 336. We did this in two steps and an overall

yield of 62% beginning with the natural product geraniol (334) (Scheme 4.05).

* The tosyl group is a common protecting group for free pyrroles which are highly reactive towards

electrophilic substitution and sensitive to acid-catalysed polymerisation. The electron-withdrawing tosyl

group diminishes the aromatic character of the pyrrole and provides stability against acidic conditions.353

144

Scheme 4.05. Reagents and conditions: a) VO(acac)2 (5 mol%), t-BHP (1.2 eq),CH2Cl2, rt, 1 h, 83%;

b) IBX (3 eq), EtOAc, reflux, 3 h, 75%.

Geraniol (334) was treated with VO(acac)2 and t-BHP in dichloromethane to give epoxy

alcohol 335 in 83% yield (Scheme 4.05). Epoxy alcohol 335 was then treated with IBX

to give aldehyde 336 in 75% yield (Scheme 4.05). The spectroscopic data for 335355

and 336356

matched that reported previously in the literature.

With access to aldehyde 336 we could then focus on the synthesis of a vinyl halide

coupling-partner. Our initial investigations into the synthesis of a vinyl halide coupling

partner began with the attempted synthesis of (E)-vinyl iodide oxirane 337

(Scheme 4.05). To begin, we attempted the synthesis of vinyl iodide 337 via a Wittig

reaction. Considering that iodomethyl triphenylphosphonium iodide 260 (the

phosphonium salt required for the synthesis of the desired vinyl iodide 337) was

without any stabilising substituents, the established literature predicted that the

treatment of aldehyde 336 with 260 would give rise to a cis-substituted vinyl iodide

(Scheme 4.06).357,358

Scheme 4.06. The stereochemistry of the alkene is determined by the oxaphosphetane-forming step.359

145

The experiment provided the (Z)-vinyl iodide 337 exclusively in 66% yield, after

aldehyde 336 was treated with phosphonium salt 260 under standard literature

conditions (Scheme 4.07).

Scheme 4.07. Reaction conditions: a) 260 (1.2 eq), THF, NaHMDS (1.2 eq), -78°C, rt, 30 min, 66%.

Particularly diagnostic for the formation of cis-vinyl iodide 342 was the absence of a

resonance signal in the aldehyde region, and the appearance of resonance signals

observed at δ = 6.54 and 6.23 ppm (J = 7.8 Hz) in the 1H NMR spectrum which were

assigned to the cis-olefinic protons H-1 and H-2.

It is known that lithium salts induce the formation of the trans-oxaphosphetane

intermediate 338 resulting in increased formation of the (E)-alkene, at the expense of

the (Z)-alkene, even if the ylid is un-stabilised (Scheme 4.06).360,361

Hence, aldehyde

336 was treated with various lithium salts, phosphonium salt 260, and modified Wittig

conditions using a lithium base in an attempt to access the (E)-vinyl iodide oxirane 337

(Scheme 4.08).

Scheme 4.08. Reactions and conditions: a) 260 (1.2 eq), THF, LiHMDS (1.2 eq), -78°C, rt, 30 min;

b) 260 (1.2 eq), THF, LiHMDS (1.2 eq), LiBr (1.4 eq), -78°C, rt, 30 min.

In both cases, the reaction gave a 50:50 mixture of what appeared to be the cis-isomer

(as determined by signals in the crude 1H NMR) and an unknown by-product.

Unfortunately, the two products could not be separated via silica or alumina gel column

146

chromatography because of their low polarities. Additionally, no resonance signals that

could be assigned to the trans-isomer were evident in the 1H NMR spectrum of the

crude mixture. Thus, the structure of the by-product remained a mystery and due to time

constraints could not be investigated further. In the future, we intend to identify the

structure of the compound after separating the two compounds by using either

preparatory HPLC or via purification on reverse phase silica gel.

Given the high Rf value of the product mixture by TLC analysis (Rf = 0.89 in 20:80

EtOAc/hexane), we assumed that the epoxide group was still intact in both products. As

a result, the crude mixture was exposed to various standard epoxide ring opening

procedures in an attempt to synthesise the more polar diol derivatives for more facile

purification via column chromatography. The results are summarised in Table 4.01.

Table 4.01. Attempted diol formation

Entry Reagent Solvent Temp Time Reaction outcome

1 H2SO4

(5 mol%)

THF/H2O

(50:50)

65°C 1 h Complex mixture

2 NaOH

(10% w/w aq) THF reflux 18 h No reaction

3 HClO4

(5 mol%)

THF/H2O

(50:50) 0°C 1 h Complex mixture

Unfortunately, the results of the attempted epoxide ring opening reactions did not help

us to elucidate the structure of the by-product. Given the lack of success with the Wittig

reaction for forming the desired vinyl iodide, we decided to explore alternative options.

A second approach to the required vinyl iodide 337 was conceived through a terminal

alkyne precursor 344 using the Takai olefination protocol (Scheme 4.09).362,363

147

Scheme 4.09. Reagents and conditions: a) i) CBr4 (2 eq), PPh3 (2 eq), NEt3 (1 eq), -78°C → 20°C, 4 h

ii) n-BuLi (2 eq), THF, -78°C, 76%; b) CrCl2 (2 eq), CHI3 (3 eq), THF, 0°C → 20°C, 18 h,

decomposition; c) DIBAL-H (1.5 eq), hexane, 55°C, 6 h → I2 (1.1 eq), THF, 20°C, 12 h, no reaction.

Firstly, alkyne 344 was obtained in 76% yield after treating aldehyde 336 with CBr4,

PPH3, and NEt3 under modified Corey-Fuchs conditions developed by Grandjean et al.

(Scheme 4.09).336

Particularly diagnostic for the formation of terminal alkyne 344 was

the absence of a resonance signal in the aldehyde region, and the appearance of a

resonance signal observed at δ = 2.35 ppm in the 1H NMR which was assigned to the

acetylene proton. The terminal alkyne 344 was then exposed to CrCl2 and iodoform

under the conditions described by Takai et al. (Scheme 4.09).362-364

Unfortunately, the

Takai olefination did not provide any of the desired trans-vinyl iodide 337 leading

instead to decomposition of the starting material.

To alleviate the harsh conditions previously trialled, we moved on to a

hydroalumination-iodination method described by Zweifel et al. in which exposure of a

terminal alkyne to DIBAL-H results in a cis-addition of the aluminium-hydrogen bond

to give a trans-vinylalane 345 (Scheme 4.10). The trans-vinylalane (345) is then

thought to undergo electrophilic cleavage at the vinyl-carbon aluminium bond with

iodine to give the trans-vinyl iodide 346 (Scheme 4.10). 365,366

Scheme 4.10. Hydroalumination-iodination of a terminal alkyne to a trans-vinyl iodide.

148

Unfortunately, it did not appear that DIBAL-H was reactive enough to reduce the

alkyne to an olefin under the hydroalumination-iodination conditions specified as the

substrate was the only product isolated after 18 hours of reaction time (Scheme 4.09).

4.2.3 The synthesis of vinyl bromide 348

Given that our efforts to synthesise the trans-vinyl iodide 337 were unsuccessful, we

directed our efforts towards the synthesis of the trans-vinyl bromide 348. It had come to

our attention that Grandjean et al. had discovered a method to synthesise (E)-

bromoalkenes from 1,1-dibromoalkenes, in a highly stereoselective manner using 1

equivalent of MeLi* in THF at -100°C.

367 We applied this methodology to synthesise

(E)-bromoalkene 348 in 2 steps and an overall yield of 56% starting from aldehyde 336

(Scheme 4.11).

Scheme 4.11. Reagents and conditions: a) i) CBr4 (2 eq), PPh3 (2 eq), NEt3 (1 eq), -78°C → 20°C, 4 h,

87%; b) i) MeLi (1 eq), THF, -100°C, 5 min → MeOH, 37% w/w aq NH4Cl ii) CuI (1 eq), 31% w/w aq

NH3, EtOH, 20°C, 15 min, 57%.

Firstly, aldehyde 336 was treated with CBr4, PPh3, and NEt3 to give dibromoalkene 347

in excellent yield (87%) (Scheme 4.11).336

Particularly diagnostic for the formation of

dibromo alkene 347 was the absence of a resonance signal in the aldehyde region, and

the appearance of a resonance signal observed at δ = 6.31 ppm in the 1H NMR which

was assigned to the olefinic proton H-2.

* Grandjean et al. showed that the nature of the organolithium species greatly influences the

stereochemical outcome of the reaction. The use of n-butyl, t-butyl, and phenyl-lithium reagents, showed

a lower stereoselectivity for the (E)-isomer, relative to the use of MeLi. However, in all cases, the (E)-

isomer was still predominant.367

149

The dibromoalkene 347 was then exposed to (E)-bromoalkene selective reaction

conditions to give what 1H NMR analysis showed to be a 2:6 mixture of the alkyne 344

and the trans-vinyl bromide 348 (Scheme 4.11).367

The preference for (E)-isomers

when trisubstituted 1,1-dibromoaalkenes are treated with lithium reagents has been

proposed to be due to steric effects.367

In the case of dibromovinylepoxide precursors

stereoselectivity has been proposed to be due to a chelation effect of lithium with the

oxygen atom of the oxirane ring.367-370

Unfortunately, despite several attempts, the alkyne 344 and trans-bromoalkene 348

could not be separated via standard silica or alumina gel column chromatography due to

their low polarities. As a result, we decided to separate the products by filtering off the

alkyne as its cuprous acetylide derivative. Copper(I) acetylides can be prepared from

copper(I) iodide and acetylenes in ammonia solutions via the methodology developed

by Castro and Stephens.371

Thus, an aqueous ammonia solution of copper(I) iodide was

poured into a solution containing a mixture of the crude alkyne 344 and (E)-

bromoalkene 348 in ethanol. After the reaction mixture was allowed to stand for 15

minutes, the bright yellow precipitate that formed was filtered off, the filtrate was

concentrated in vacuo, and then the crude product was purified to give exclusively the

trans-bromo alkene 348 in 57% yield (Scheme 4.11).

Particularly diagnostic for the synthesis of 348 were the appearance of resonance signals

at δ = 6.41 and 6.12 in the 1H NMR spectrum that showed trans-coupling (J = 13.8 Hz),

and were assigned to the olefinic protons H-1 and H-2 (Scheme 4.11). Thus, vinyl

bromide 348 was synthesised in 4 steps and 31% overall yield starting from geraniol.

4.2.4 Attempted Heck cross-coupling between vinyl bromide 348 and acrylate

329

With substrates 348 and 329 in hand, we made an attempt to synthesise the precursor

325 via an inter-molecular Heck cross-coupling reaction. Thus, vinyl halide 348 and

olefin 329 were exposed to several standard Heck cross-coupling conditions.50

The

results are summarised in Table 4.02.

150

Table 4.02. Attempted Heck reactions between 348 and 329

Reagents and conditions: Catalyst (10 mol%), ligand (20 mol%), base (3 eq), solvent, rt, 18 h.

Entry Catalyst Ligand Base Solvent Outcome

1 Pd(PPh3)4 - KOAc DMF NR

2 PdCl2(PPh3)2 - NEt3 DMF NR

3 Pd2(dba)3.CHCl3 P(t-Bu)3HBF4 Cy2NMe THF NR

NR = No reaction.

It appeared that 348 was not a reactive enough vinyl bromide coupling partner to enable

successful oxidative addition under the conditions trialled. Oxidative addition, generally

thought to be the rate limiting step in most cross-coupling catalytic cycles, is assisted by

the use of electron-withdrawing substituents on the vinyl bromide coupling partner. It

was presumed that the presence of an electron-donating substituent on the vinyl

bromide 348 greatly decreased its reactivity. The addition of a bulky electron-rich

tertiary phosphine (P-tBu3) on palladium (conditions developed by Fu et al.)90

also

failed to induce oxidative addition (entry 3, Table 4.02). In all cases unreacted starting

material was recovered. Due to time constraints, and because of the low overall yield of

the trans-vinyl bromide 348, we did not trial additional Heck cross-coupling reaction

conditions. However, in the future we hope to revisit the reaction with more reactive

catalytic conditions.

151

4.3 The attempted synthesis of glaciapyrrole B (322) via a key Heck

cross-coupling reaction

Epoxides are quite reactive substrates, and generally react unfavourably if unprotected.

Thus, we also simultaneously investigated the synthesis of a vinyl halide coupling

partner with the epoxide group masked as an acetonide. As highlighted in the

retrosynthetic analysis in Scheme 4.12 we believed that the acetonide could be directly

converted into the diol functionality observed in the natural product 322.

Scheme 4.12. Retrosynthetic analysis of glaciapyrrole C (322).

4.3.1 The attempted synthesis of vinyl bromide 357

Considering our earlier attempts to synthesise vinyl bromide 348 from dibromoalkene

347 had been successful, we decided to repeat the methodology developed by

Grandjean et al. to obtain the acetonide vinyl bromide 357. In order to synthesise 357,

we needed to access the dibromo alkene 356 from aldehyde 355. Thus, our first step

was to synthesise aldehyde 355, which we did in 5 steps and an overall yield of 34%

(Scheme 4.13).

152

Scheme 4.13. Reagents and conditions: a) Ac2O (1.3 eq), NEt3 (1.4 eq), DMAP (2 mol%), CH2Cl2 20°C,

30 min, 98%; b) 70% aq HClO4 (10 mol%), THF/H2O (60:30), 100°C, 15 min, 49%;

c) 2,2-dimethoxypropane (2.3 eq), acetone (1.3 eq), p-TsOH (5 mol%), 20°C, 30 min, 96%; d) K2CO3

(3 eq), H2O/MeOH (1:2), 100°C, 3 h, 91%; e) IBX (3 eq), EtOAc, reflux, 4 h, 82%.

To begin, epoxide 334 was acetylated under standard conditions to provide acetate 351

in 98% yield (step a, Scheme 4.13). The spectroscopic data for 351 matched that

reported previously in the literature.290

This was followed by epoxide cleavage of 351

using catalytic HClO4 in THF/H2O (6:3) to give diol 352 in 49% yield

(step b, Scheme 4.13). Diol 352 was the major spot isolated from a complex mixture.

1H NMR analysis indicated that diol 352 was a single diastereoisomer. However, no

further studies were performed to determine which diastereoisomer. Particularly

diagnostic for the synthesis of diol 352 were the appearance of two broad resonance

signals at δ = 2.23 and 1.82 in the 1H NMR spectrum that were assigned to the two

hydroxyl protons.

The diol was then protected to give acetonide 353 in 96% yield (step c, Scheme 4.13).

Particularly diagnostic for the synthesis of 353 were the appearance of two resonance

signals in the 1H NMR spectrum that were assigned to the two acetonide methyl groups.

153

Base-catalysed saponification of acetate 353 gave primary alcohol 354 in 91% yield

(step d, Scheme 4.13). The formation of primary alcohol 354 was indicated by the

absence of a resonance signal in the carbonyl region of the 13

C NMR spectrum, and by

the appearance of a resonance signal at δ = 1.75 ppm in the 1H NMR spectrum that was

assigned to the hydroxyl group, This step was followed by an IBX oxidation of primary

alcohol 354 to provide aldehyde 355 in 82% yield (step e, Scheme 4.13). Particularly

diagnostic for the synthesis of 355 were the appearance of resonance signals at δ = 9.74

and 200.5 ppm in the 1H NMR and

13C NMR spectra that were assigned to the aldehyde

group, respectively.

Aldehyde 355 was then treated with CBr4, PPh3 and NEt3 under the modified Ramirez

conditions developed by Grandjean et al.336

to give dibromoalkene 356 in 75% yield

(Scheme 4.14). The synthesis of dibromoalkene 356 was indicated by the appearance of

a resonance signal observed at δ = 6.49 ppm in the 1H NMR, which was assigned to the

vinyl proton (-CH=CBr2).

Scheme 4.14. Reagents and conditions: a) i) CBr4 (2 eq), PPh3 (2 eq), NEt3 (1 eq), -78°C → 20°C, 4 h,

75%; b) i) MeLi (1 eq), THF, -100°C, 5 min → MeOH, 37% w/w aq NH4Cl ii) CuI (1 eq), 31% w/w

aq NH3, ethanol, 20°C, 15 min, 65%.

The dibromoalkene 356 was then exposed to the (E)-bromoalkene selective reaction

conditions described earlier to give a mixture of what 1H NMR analysis indicated to be

the alkyne 358, the trans-vinyl bromide 357, and the cis-vinyl bromide (Scheme 4.14).

The cis- and trans-vinyl bromides were separated from the alkyne 358, after the alkyne

154

was filtered off as its copper (I) acetylide derivative. Unfortunately, the cis- and trans-

isomers could not be separated using standard chromatography techniques.

4.3.2 Attempted Heck reactions between vinyl bromide 357 and acrylate 329

Despite being unable to separate what appeared to be the cis- and trans-vinyl bromide

isomers, we subjected the mixture to Heck cross-coupling reaction conditions on the

chance that the desired product might form and be isolable. Thus, the vinyl bromide

mixture and olefin 329 were exposed to several standard Heck cross-coupling reaction

conditions. The results are summarised in Table 4.03 below.

Table 4.03. Attempted Heck reactions between 357 and 329

Reagents and conditions: Catalyst (10 mol%), ligand (20 mol%), base (3 eq), solvent, rt, 18 h.

Entry Catalyst Ligand Base Solvent Outcome

1 Pd(PPh3)4 - KOAc DMF NR

2 PdCl2(PPh3)2 - NEt3 DMF NR

3 Pd2(dba)3.CHCl3 P(t-Bu)3HBF4 Cy2NMe THF Inseparable

The standard Heck cross-coupling conditions using Pd(PPh3)4 and PdCl2(PPh3)2 as

catalysts showed no reaction (entries 1 and 2, Table 4.03). The coupling conditions

using Pd2(dba)3 in the presence of the electron-rich phosphine P-t-Bu3 resulted in an

inseparable mixture (entry 3, Table 4.03). Due to the lack of apparent selectivity in

producing the desired trans-isomer 357 and because the Heck reactions appeared to be

unsuccessful, we discontinued the pursuit of pathways for the total syntheses of natural

products 322 and 323 using the Heck reaction as a key step.

155

4.4 The attempted synthesis of glaciapyrrole C (323) via a key

Suzuki cross-coupling reaction

Our next approach to glaciapyrrole C (323) attempted to take advantage of a Suzuki

cross-coupling reaction to establish the C-(sp2)-C(sp

2) bond between C8 and C9

(Scheme 4.15).

Scheme 4.15. Retrosynthetic analysis of glaciapyrrole C (323).

As mentioned earlier, oxidative addition is considered to be the rate limiting step in a

number of Pd(0)-catalysed cross-coupling reactions. Generally speaking, aryl or vinyl

halides with electron-withdrawing substituents lead to enhanced rates of oxidative

addition. Since the electron-rich vinyl bromide 348 used earlier was unsuccessful in

reactions using standard Heck catalytic conditions, we decided to trial vinyl iodide 327

as an electrophilic coupling partner instead. We reasoned that 327 would make a better

electrophilic coupling partner because of the electron-withdrawing group attached to the

alkene.50

Thus, our first step in the newly proposed sequence was to prepare vinyl

iodide 327 as a precursor.

156

4.4.1 The synthesis of vinyl iodide 327

The desired vinyl iodide coupling partner 327 was synthesised in 4 steps and 34%

overall yield starting from 1H-pyrrole-2-carbaldehyde 360 (Scheme 4.16).

Scheme 4.16. Reagents and conditions: a) NaH (1.2 eq), THF, p-TsCl (1.4 eq), rt, 18 h, 87%; b) 362

(1.2 eq), THF, 0°C, 1 h → 37% w/w aq NH4Cl, 94%; c) IBX (3 eq), EtOAc, reflux, 5 h, 91%;

d) LiI (3.3 eq),CH3CN, AcOH (8.9 eq), 70°C, 24 h, 39% (327) 46% (365).

To begin, N-tosyl-protected pyrrole 361 was synthesised in 87% yield after treatment of

carbaldehyde 360 with sodium hydride and toluenesulfonyl chloride (Scheme 4.16).

The spectroscopic data for 361 matched that reported previously in the literature.372

This

was followed by treatment of the N-tosyl-protected pyrrole 361 with Grignard reagent

362 to give propargyl alcohol derivative 363 in 94% yield. Particularly diagnostic for

the formation of 363 were the appearance of resonance signals at δ = 111.6 (C C),

82.1 (C C), 77.0 (COH) and 3.6 (CH3) ppm in the 13

C NMR spectrum which were

assigned to the propargyl alcohol chain.

The propargyl alcohol 363 was then oxidised to acetylenic ketone derivative 364 in 91%

yield. The formation of 364 was indicated by the appearance of a resonance signal at

δ = 164.6 (C=O) ppm in the 13

C NMR spectrum. With the acetylenic ketone derivative

364 in hand, we turned our attention to the preparation of the vinyl halide coupling-

157

partner 327. Through a series of trial reactions, the most efficient conditions were found

to be between 364 with lithium iodide in acetic acid and acetonitrile to give a mixture of

327 and 365 in 39% and 46% yields, respectively. The (E)-and (Z)-isomers showed a

large difference in Rf on silica gel and were easily separable via standard silica gel

column chromatography. Spectroscopic data indicated the formation of 327 and 365. An

X-ray crystal structure obtained for 327 allowed us to differentiate between each

structural isomer (Figure 4.03).

Figure 4.03. A single X-ray crystal structure ORTEP (50% probability) of 327.

The synthesis of vinyl iodide isomers 327 and 365 from the acetylenic ketone 364 was

believed to proceed via the mechanism proposed in Scheme 4.17.373

Nucleophilic attack

of iodide from either face of the planar carbocation intermediate 367 was believed to be

responsible for the formation of both the cis- and trans-viny iodide isomers 327 and

365.

158

Scheme 4.17. Proposed mechanism for the formation of cis- and trans-vinyl iodides from an acetylenic

ketone.373

4.4.2 The attempted synthesis of epoxy boronic acids and esters

Several common synthetic methods for accessing boronic acids and esters were

considered when attempting to synthesise an epoxy vinyl boronic acid or ester coupling

partner for use in future Suzuki reactions.85

The first method trialled focused on a

lithium-bromine exchange reaction between vinyl bromide 348 and n-BuLi, followed by

electrophilic trapping with dioxaborolane 51. Unfortunately, instead of the desired

boronic ester, the reaction gave an inseparable mixture of compounds (Scheme 4.18).

Scheme 4.18. Reactions and conditions: a) n-BuLi (1 eq), THF, 51 (1.1 eq), -78°C, 30 min, inseparable

mixture.

Our next attempts towards the synthesis of boronic acid coupling partners 359 and 367

focused on trans-selective hydroboration reactions between terminal alkynes 344 and

358 with dibromoborane-dimethyl sulfide.374

Unfortunately, exposing terminal alkynes

159

344 and 358 to standard literature conditions involving dibromoborane-dimethyl sulfide

resulted in decomposition of the starting material (Scheme 4.19).

Scheme 4.19. Reaction and conditions: a) Br2BH.SMe2 (1 eq), CH2Cl2, 0°C, 30 min, inseparable mixture;

b) n-BuLi (2 eq), THF, -78°C, 73%; b) Br2BH.SMe2 (1 eq), CH2Cl2, 0°C, 30 min, inseparable mixture;

c) PdCl2(PPh3)2.2PPh3 (3 mol%), KOPh (1.5 eq), toluene, 50°C.

Due to time constraints, we did not attempt to synthesise the boronic ester 366 from a

cross-coupling reaction between vinyl bromide 348 and bis(pinacolato)diboron 14 using

the Miyaura-borylation protocol, because our earlier efforts at using vinyl bromide 348

as an electrophilic coupling partner were unsuccessful (reaction 3, Scheme 4.19).94,375

Our initial efforts to synthesise a boronic acid or ester coupling partner to react with

vinyl iodide 327 were unsuccessful (Scheme 4.19) and due to time constraints we could

not pursue any further reactions. As a result, we could not trial any Suzuki cross-

coupling reactions to attempt the synthesis of the natural product precursors 325 or 349.

However we do feel that the synthesis of boronic acid or ester coupling partners (359,

366, and 367) are worth pursuing in the future.

160

161


In summary, we were unable to achieve a total synthesis for either glaciapyrrole B or

glaciapyrrole C. The Heck cross-coupling was ruled out as a key reaction step because

we did not believe that it could be used to achieve a stereospecific reaction outcome.

However, we do feel that the Suzuki cross-coupling has potential as a key reaction step,

if we are able to synthesise an appropriate vinyl epoxy boronic acid or ester coupling

partner (such as 359 or 367) to react with vinyl iodide 327 (Scheme 4.20).

Scheme 4.20. A potential intermolecular Suzuki cross-coupling reaction could be used to establish the

C-(sp2)-C(sp

2) bond between C8 and C9.

In the future, we also plan to attempt Sonogashira and Castro-Stephens cross-coupling

reactions to establish a C-(sp1)-C(sp

2) bond between C8 and C9 (Scheme 4.21). We then

intend to test out a number of reduction methods to establish a trans-selective

C-(sp2)-C(sp

2) bond between C8 and C9 to give us 325, a precursor to glaciapyrrole C.

162

Scheme 4.21. A potential intermolecular Sonogashira cross-coupling as a key reaction step in the

synthesis of glaciapyrrole C (323).

163

Chapter 5

Experimental Section

164

165

5.1 General experimental

All reactions were carried out under an argon gas atmosphere in flame-dried glassware

with magnetic stirring, unless otherwise stated. All reaction temperatures refer to bath

temperatures: -78°C was achieved in an acetone/dry ice bath; 0°C was achieved in a

H2O ice bath. All reactions involving heating were placed into a preheated oil bath at

the specified temperature, unless otherwise stated. Solvents were used dry, unless

otherwise stated. Solvents were dried and purified according to the methods described

by Armarego and Chai.376

All palladium-catalysed cross-coupling reactions were carried

out using de-gassed solvents. All reagents were purchased from Sigma-Aldrich, Fluka,

Merck, or Boron Molecular and used without further purification, unless otherwise

stated.

Thin layer chromatography (TLC) was performed on Merck silica gel 60 F254 pre-coated

aluminium sheets. Visualisation of developed plates was achieved through the use of a

254 nm or 365 nm UV lamp or staining with phosphomolybdic acid stain solution.

Column chromatography was performed using silica gel 60 (0.063-0.200 nm) as

supplied by Merck, unless otherwise stated.

1H and

13C NMR spectra were acquired in the specified deuterated solvent using either a

Bruker AV600 (600.13 MHz for 1H and 150.9 MHz for

13C), a Bruker AV500 (500.13

MHz for 1H and 125.8 MHz for

13C), or a Varian Gemini-400 (399.85 MHz for

1H and

100.5 MHz for 13

C) spectrometer at 25°C. Chemical shifts are reported in parts per

million downfield from tetramethylsilane using the solvent resonance as internal

standard.377

Data are reported as follows: chemical shift, multiplicity (app = apparent,

s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad, sept = septet),

coupling constant, integration, and assignment. Structural assignment was aided by use

of HSQC and HMBC spectroscopy.

Mass spectra were acquired on a VG autoSpec instrument or a Waters liquid

chromatograph premier (LCT) mass spectrometer through electron ionisation (EI), fast

atom bombardment (FAB), or atmospheric pressure chemical ionisation (APCI).

166

Infrared (IR) spectra were recorded with a PerkinElmer Spectrum One FT-IR

spectrometer. Samples were analysed as neat samples and recorded as wave numbers

(cm-1

). Melting points were determined on a Reichert hot stage melting point apparatus.

All crystallographic data for compounds 275 and 327 can be found in the appendix

(Chapter 7).

167

5.2 Experimental for Chapter 2

1-Benzyl-3,4-dichloro-1H-pyrrole-2,5-dione (46):

A mixture of benzylamine (3.1 mL, 3.04 g, 28.4 mmol), maleic anhydride 45 (3.93 g,

23.3 mmol), and glacial AcOH (10 mL) was stirred at 55°C for 18 hours, under an

atmosphere of argon gas. After this time, the reaction mixture was diluted with 22%

w/w aq Na2CO3 (50 mL) and CH2Cl2 (50 mL). The aqueous and organic layers were

separated, and the aqueous layer was extracted further with CH2Cl2 (3 × 50 mL). The

combined organic extracts were then washed with 9% w/w aq NaHCO3 (3 × 50 mL),

dried (MgSO4), filtered, and concentrated under reduced pressure to give a yellow

residue. The crude residue was subjected to flash column chromatography to give

maleimide 46 as a colourless solid (2.72 g, 81% yield, Rf = 0.30 in 5:95 EtOAc/hexane).

The spectroscopic data for compound 46 matched that reported previously in the

literature.166,167

1-Benzyl-3-chloro-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (48):

Isobutylzinc bromide (28 mL, 0.5 M in THF, 14.0 mmol) was added drop-wise to a de-

gassed (freeze-pump-thaw × 3) mixture of dichloromaleimide 46 (3.52 g, 13.7 mmol),

THF (5 mL), Pd2(dba)3.CHCl3 (1.19 g, 1.09 mmol), and PPh3 (678 mg, 2.58 mmol),

stirring under an atmosphere of argon gas. The resulting mixture was stirred at reflux

for 18 hours. After this time, the reaction mixture was cooled to room temperature,

filtered through a plug of silica gel (eluted with 50:50 EtOAc/hexane), and then

concentrated under reduced pressure to give a crude residue. The crude residue was

subjected to flash column chromatography on silica gel (2:98 EtOAc/hexane) to give

the desired isobutylmaleimide 48 (2.28 g, 60% yield, Rf = 0.35 in 5:95 EtOAc/hexane).

168


literature.166,167

General procedure for the Williamson ether synthesis:

Alkyl bromide (1.2 eq) was added to a stirring suspension of K2CO3 (2 eq) in acetone.

The resulting mixture was stirred at reflux for 16 hours. After this time, the solvent was

removed in vacuo and the reaction mixture was diluted with EtOAc and water. The

aqueous and organic layers were separated and the aqueous layer was extracted further

with EtOAc. The combined organic layers were washed with brine, dried (MgSO4), and

concentrated in vacuo to give a crude oil which was subjected to silica gel column

chromatography to give the pure aryl ether products.

1-Bromo-4-(3-methylbutoxy)benzene (59):

The general procedure for the Williamson ether synthesis was followed using phenol 52

(2.52 g, 14.5 mmol). The crude material was subjected to column chromatography (5:95

EtOAc/hexane) to give compound 59 (2.50 g, 70% yield) as a colourless oil.

(59): 1H NMR (399.85 MHz, CDCl3): δ = 7.35 (app d, 2H, 2 × ArH), 6.78 (app d,

2H, 2 × ArH), 3.95 (t, J = 6.5 Hz, 2H, OCH2), 1.83 (app sept, 1H, CH(CH3)2), 1.67 (dt,

J = 6.5 Hz, 2H, OCH2CH2), 0.97 (s, 6H, 2 × CH3); 13

C NMR (100.5 MHz, CDCl3): δ =

158.2 (ArC) 132. 1 (ArCH), 116.3 (ArCH), 112.5 (ArC), 66.6 (OCH2), 37.8

(OCH2CH2), 25.0 (CH), 22.7 (2 × CH3); HRMS (EI): calc. for C11H15BrO [M]+

242.0306, found 242.0302.

1-Bromo-4-(pentyloxy)benzene (61):

169

The general procedure for the Williamson ether synthesis was followed using

phenol 52 (2.36 g, 13.6 mmol). The crude material was subjected to column

chromatography (5:95 EtOAc/hexane) to give compound 61 (2.02 g, 61% yield) as a

colourless oil. (61): 1H NMR (399.85 MHz, CDCl3): δ = 7.38 (app d, 2H, 2 × ArH),

6.79 (app d, 2H, 2 × ArH), 3.91 (t, J = 6.4 Hz, 2H, OCH2), 1.83-1.76 (m, 2H), 1.50-1.36

(m, 4H), 0.97 (t, J = 6.4 Hz, 3H, CH3); 13

C NMR (100.5 MHz, CDCl3): δ = 158.5

(ArC), 132.4 (ArCH), 116.5 (ArC), 112.8 (ArCH), 68.4 (OCH2), 29.2 (OCH2CH2), 28.4

(OCH2CH2CH2), 22.7 (OCH2CH2CH2CH2), 14.3 (CH3); HRMS (EI): calc. for

C11H15BrO [M]+ 242.0306, found 242.0300.

General procedure for the synthesis of boronic acids:

n-BuLi (1 eq) was added in one portion to a solution of aryl ether (1 eq) and THF

stirring at -78°C, under an argon gas atmosphere. The ensuing yellow reaction mixture

was stirred for 15 minutes at this same temperature before the addition of

trimethylborate 50 (1.1 eq) in one portion. The reaction was then stirred for 5 minutes at

-78°C, before being allowed to stir at room temperature for 2 hours. After this time

period, the reaction mixture was quenched with 1 M aq HCl, stirred for 15 minutes at

room temperature and then extracted with Et2O (× 3). The combined organic extracts

were dried (MgSO4), filtered, concentrated under reduced pressure, and subjected to

silica gel flash column chromatography to give the target boronic acids.

General procedure for the synthesis of boronic esters:

n-BuLi (1 eq) was added in one portion to a solution of aryl ether (1 eq) and THF

stirring at -78°C, under an argon gas atmosphere. The ensuing yellow reaction mixture

was stirred for 15 minutes at this same temperature before the addition of dioxaborolane

51 (1.1 eq) in one portion. The reaction was then stirred for 5 minutes at

170

-78°C, before being allowed to stir at room temperature for 2 hours. After this time

period, the reaction mixture was quenched with ice water, stirred for 15 minutes at room

temperature, and then extracted with Et2O (× 3). The combined organic extracts were

dried (MgSO4), filtered, concentrated under reduced pressure, and subjected to silica gel

flash column chromatography to give the target boronic acids.

4,4,5,5-Tetramethyl-2-(4-(pentyloxy)phenyl)-1,3,2-dioxaborolane (75):

The general procedure for the synthesis of boronic esters was followed using

dioxaborolane 51 (1.49 g, 8.00 mmol) and bromo aryl ether 61 (1.77 g, 7.28 mmol). The

crude material was subjected to column chromatography (5:95 EtOAc/hexane) to give

compound 75 (1.54 g, 73% yield) as a colourless oil. (75): 1H NMR (399.85 MHz,

CDCl3): δ = 7.77 (app d, 2H, 2 × ArH), 6.90 (app d, 2H, 2 × ArH), 3.98 (t, J = 6.4 Hz,

2H, OCH2), 1.84-1.77 (m, 2H), 1.51-1.37 (m, 4H), 1.35 (s, 12H, 4 × CH3), 0.95 (t, J =

7.2 Hz, 3H, CH3); 13

C NMR (100.5 MHz, CDCl3): δ = 161.9 (ArC), 136.6 (ArCH),

114.0 (ArCH), 83.6 (C), 67.9 (OCH2), 29.0 (OCH2CH2), 28.3 (OCH2CH2CH2), 25.0

(CH3), 22.6 (OCH2CH2CH2CH2), 14.1 (CH3); HRMS (EI): calc. for C17H28BO3 [M +

H]+ 291.2131, found 291.2132. IR (neat): ν = 2957, 1605, 1361 (B-O), 1247cm

-1.

General procedure for the Suzuki reaction of vinyl maleimides:

A mixture of chloromaleimide 48 (1 mmol), PdCl2(dppf) (11 mol%), THF (2 mL),

NaOH (3 mmol in 300 µL H2O), and the desired boronic acid or ester (1.2 mmol) was

de-gassed via the freeze-pump-thaw method (× 3) and then left to stir at reflux for 18

hours, under an atmosphere of argon gas. After this time, the reaction mixture was

diluted with EtOAc (3 mL), filtered through a plug of silica gel (eluted with 50:50

EtOAc/hexane), and then concentrated under reduced pressure to give a crude residue.

171

The crude residue was subjected to flash column chromatography on silica gel

(EtOAc/hexane) to give the desired arylmaleimide.

1-Benzyl-3-isobutyl-4-(4-isopropoxyphenyl)-1H-pyrrole-2,5-dione (78):

The general procedure for the Suzuki reaction was followed using chloromaleimide 48

(166 mg, 0.60 mmol) and boronic ester 71 (189 mg, 0.72 mmol). The crude material

was subjected to column chromatography (5:95 EtOAc/hexane) to give compound 78

(125 mg, 55% yield, Rf = 0.50 in 20:80 EtOAc/hexane) as a fluorescent yellow oil. (78):

1H NMR (399.85 MHz, CDCl3): δ = 7.46 (app d, 2H, 2 × ArH), 7.35–7.20 (m, 5H, 5 ×

ArH), 6.88 (app d, 2H, 2 × ArH), 4.67 (s, 2H, CH2Ph), 4.55 (sept, J = 6.4 Hz, 1H,

OCH(CH3)2), 2.46 (d, J = 7.6 Hz, 2H, CH2CH(CH3)2), 2.01 (m, 1H, CH2CH(CH3)2),

1.31 (d, J = 6.4 Hz, 6H, 2 × CH3), 0.84 (d, J = 6.4 Hz, 6H, 2 × CH3); 13

C NMR (100.5

MHz, CDCl3): δ = 172.2 (C=O), 171.5 (C=O), 159.3 (C), 138.3 (C), 138.1 (C), 137.0

(C), 131.3 (ArCH), 128.9 (ArCH), 128.8 (ArCH), 128.0 (ArCH), 121.5 (C), 115.9

(ArCH), 70.2 (OCH(CH3)2), 42.0 (CH2Ph), 33.2 (CH2), 28.4 (CH), 23.1 (CH3), 22.3

(CH3); MS (EI) (m/z): 377 [M]+ (99), 335 (90), 292 (45), 244 (48), 215 (53), 131 (78);

HRMS (EI): calc. for C24H27NO3 [M]+ 377.1991, found 377.1989; IR (neat): ν = 2959,

1702 (C=O), 1605, 1509, 1401, 1251, 1185, 1110, 1012, 953, 699 cm-1

.

172

1-Benzyl-3-isobutyl-4-(4-(pentyloxy)phenyl)-1H-pyrrole-2,5-dione (81):





1H NMR (399.85 MHz, CDCl3): δ = 7.51 (app d, 2H, 2 × ArH), 7.40-7.25 (m, 5H, 5 ×

ArH), 6.95 (app d, 2H, 2 × ArH), 4.72 (s, 2H, CH2Ph), 4.00 (t, J = 6.4 Hz, 2H, OCH2),

2.52 (d, J = 7.6 Hz, 2H, CH2CH(CH3)2), 2.10-1.99 (m, 1H, CH), 1.86-1.74 (m, 2H,

CH2), 1.49-1.35 (m, 4H, 2 × CH2), 0.96 (d, J = 6.4 Hz, 3H, CH3), 0.89 (d, J = 6.4 Hz,

6H, CH2CH(CH3)2); 13

C NMR (100.5 MHz, CDCl3): δ = 172.1 (C=O), 171.3 (C=O),

160.5 (C), 138.4 (C), 137.0 (C), 131.3 (ArCH), 129.0 (ArCH), 128.8 (ArCH), 128.7

(ArCH), 128.0 (C), 127.5 (C), 114.9 (ArCH), 68.4 (OCH2), 42.3 (CH2Ph), 33.3 (CH2),

29.2 (CH2), 28.5 (CH2), 28.4 (CH), 23.1 (CH3), 22.8 (CH2), 14.3 (CH3); MS (EI) (m/z):

406 [M + H]+ (29), 405 [M]

+ (100), 362 (34), 335 (13), 314 (16), 292 (34), 215 (18),

205 (8), 159 (22), 131 (44); HRMS (EI): calc. for C26H31NO3 405.2304, found

405.2313; IR (neat): ν = 2957, 2932, 2870, 1704 (C=O), 1605, 1512, 1433, 1401, 1351,

1253, 1179, 699 cm-1

.

173

1-Benzyl-3-(4-(benzyloxy)phenyl)-4-isobutyl-1H-pyrrole-2,5-dione (82):





1H NMR (399.85 MHz, CDCl3): δ = 7.47 (app d, 2H, 2 × ArH), 7.39–7.16 (m, 10H, 10

× ArH), 6.99 (app d, 2H, 2 × ArH), 4.67 (s, 2H, CH2Ph), 5.04 (s, 2H, CH2Ph), 2.46 (d, J

= 7.2 Hz, 2H, CH2CH(CH3)2), 2.00 (m, 1H, CH2CH(CH3)2), 0.84 (d, J=6.4 Hz, 6H,

CH2CH(CH3)2); 13

C NMR (100.5 MHz, CDCl3): δ = 171.9 (C=O), 171.2 (C=O), 159.9

(C), 138.4 (C), 137.6 (C), 136.6 (C), 136.4 (C), 131.1 (ArCH), 128.8 (ArCH), 128.7

(ArCH), 128.6 (ArCH), 128.2 (ArCH), 127.8 (ArCH), 127.6 (ArCH), 121.9, 115.1

(ArCH), 70.2 (ArCH), 41.8 (CH2Ph), 33.0 (CH2), 28.2 (CH), 22.9 (CH3); MS (EI)

(m/z): 425 [M]+ (100), 257 (8), 131 (9); HRMS (EI): calc. for C28H27NO3 [M]

+

425.1991, found 425.1991; IR (neat): ν = 2957, 1701 (C=O), 1604, 1510, 1401, 1249,

1178, 697 cm-1

.

174

1-Benzyl-3-(4-(dimethylamino)phenyl)-4-isobutyl-1H-pyrrole-2,5-dione (83):




(202 mg, 58% yield, Rf = 0.52 in 10:90 EtOAc/hexane) as a red solid. (83): 1H NMR

(399.85 MHz, CDCl3): δ = 7.55 (app d, 2H, 2 × ArH), 7.36–7.18 (m, 5H, 5 × ArH), 6.68

(app d, 2 × ArH), 4.68 (s, 2H, CH2Ph), 2.96 (s, 6H, N(CH3)2), 2.52 (d, J = 7.0 Hz, 2H,

CH2CH(CH3)2), 2.04 (m, 1H, CH2CH(CH3)2), 0.88 (d, J = 6.4 Hz, 6H, CH2CH(CH3)2);

13C NMR (100.5 MHz, CDCl3): δ = 172.4 (C=O), 171.6 (C=O), 150.9 (C), 137.8 (C),

137.0 (C), 135.0 (C), 130.8 (ArCH), 128.6 (ArCH), 128.4 (ArCH), 127.6 (ArCH), 116.9

(C), 111.6 (ArCH), 41.6 (CH2Ph), 40.1 (N(CH3)2), 33.0 CH2), 28.1 (CH), 22.9 (CH3);

MS (EI) (m/z): 362 [M]+ (75), 320 (24), 319 (100), 245 (24), 203 (28), 186 (40), 158

(38); HRMS (EI): calc. C23H26N2O2 [M]+ 362.1994, found 362.1987; IR (neat): ν =

2956, 1760, 1698 (C=O), 1606, 1525, 1401, 1353 cm-1

.

175

1-Benzyl-3-(2-methylpropyl)-4-phenyl-1H-pyrrole-2,5-dione (84):


(289 mg, 1.04 mmol) and boronic acid 372 (152 mg, 1.25 eq). The crude material was

subjected to column chromatography (5:95 EtOAc/hexane) to give compound 84 (300

mg, 90% yield, Rf = 0.70 in 20:80 EtOAc/hexane) as a fluorescent yellow oil. (84): 1H

NMR (399.85 MHz, CDCl3): δ = 7.54-7.25 (m, 10H, ArH), 4.74 (s, 2H, CH2Ph), 2.53

(d, J = 7.2 Hz, 2H, CH2CH(CH3)2), 2.06 (m, 1H, CH2CH(CH3)2), 0.89 (d, J = 6.5 Hz,

6H, CH2CH(CH3)2); 13


140.4 (C), 138.4 (C), 136.7 (C), 129.6 (ArCH), 129.5 (ArCH), 129.2 (C), 128.8 (ArCH),

128.6 (ArCH), 128.6 (ArCH), 127.8 (ArCH), 41.9 (CH2Ph), 33.0 (CH2), 28.3 (CH),

22.8 (CH3); MS (EI) (m/z): 319 [M]+ (99), 277 (14), 228 (42), 199 (60), 115 (40);

HRMS (EI): calc. for molecular formula C21H21NO2 [M]+ 319.1572, found 319.1570;

IR (neat): ν = 2958, 2869, 1704 (C=O), 1433, 1402, 1375, 697 cm-1

.

1-Benzyl-3-(4-hydroxyphenyl)-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (85):


(317 mg, 1.14 mmol) and boronic acid 373 (189 mg, 1.37 mmol). The crude material


(230 mg, 60% yield, Rf = 0.10 in 20:80 EtOAc/hexane) as a yellow oil. (85): 1H NMR

(399.85 MHz, CDCl3): δ = 7.44–7.22 (m, 7H, 7 × ArH); 6.84 (app d, 2H, 2 × ArH), 6.36

(s, 1H, ArOH), 4.71 (s, 2H, CH2Ph), 2.48 (d, J = 7.2 Hz, 2H, CH2CH(CH3)2), 2.10 (m,

1H, CH2CH(CH3)2), 0.85 (d, J = 6.4 Hz, 6H, CH2CH(CH3)2); 13

C NMR (100.5 MHz,

176

CDCl3): δ = 172.3 (C=O), 171.6 (C=O), 157.3 (C), 138.4 (C), 138.1 (C), 136.5 (C),

131.2 (ArCH), 128.8 (ArCH), 128.5 (ArCH), 127.9 (ArCH), 121.3 (C), 115.9 (ArCH),

41.9 (CH2Ph), 33.0 (CH2), 28.3 (CH), 22.8 (CH3); MS (EI) (m/z): 335 [M]+ (99), 293

(26), 244 (35), 215 (54), 202 (12), 159 (21), 131 (68); HRMS (EI): calc. for C21H21NO3

[M]+ 335.1521, found 335.1528; IR (neat): ν = 3412 (OH), 2958, 1763, 1695 (C=O),

1608 cm-1

.

1-Benzyl-3-(4-methylphenyl)-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (86):





1H NMR (500.13 MHz, CDCl3): δ = 7.38-7.18 (m, 9H, 9 × ArH), 4.67 (s, 2H, CH2Ph),

2.45 (d, J = 6.8 Hz, 2H, CH2CH(CH3)2), 2.33 (s, 3H, ArCH3), 1.99 (sept, J = 6.8 Hz,

1H, CH2CH(CH3)2), 0.82 (d, J = 6.8 Hz, 6H, CH2CH(CH3)2); 13

C NMR (125.8 MHz,

CDCl3): δ = 171.9 (C=O), 171.0 (C=O), 139.9 (C), 139.58 (C), 138.4 (C), 136.8 (C),

129.4 (ArCH), 128.9 (C), 128.7 (ArCH), 128.6 (ArCH), 127.8 (ArCH), 126.3 (ArCH),

41.9 (CH2Ph), 33.0 (CH2CH(CH3)2), 28.3 (CH2CH(CH3)2), 22.9 (CH3), 21.6 (CH3); MS

(EI) (m/z): 334 [M + H]+ (25), 333 (100) [M]

+, 291 (19), 277 (6), 242 (40), 213 (50),

129 (44); HRMS (EI): calc. for C22H23NO2 [M]+ 333.1729, found 333.1729; IR (neat):

ν = 3452, 2956, 2869, 1703, 1433, 1401, 1350, 819, 699 cm-1

.

177

1-Benzyl-3-isobutyl-4-(4-isobutylphenyl)-1H-pyrrole-2,5-dione (87):





1H NMR (500.13 MHz, CDCl3): δ = 7.63 (app d, 2H, 2 × ArH), 7.54 (app d, 2H, 2 ×

ArH), 7.44–7.35 (m, 5H, 5 × ArH), 4.85 (s, 2H, CH2Ph), 2.67 (d, J = 7.5 Hz, 2H, CH2),

2.64 (d, J = 7.0 Hz, 2H, CH2), 2.22 (m, 1H, CH), 2.03 (m, , 1H, CH), 0.89 (d, J = 6.8

Hz, 6H, 2 ×CH3), 0.85 (d, J = 6.4 Hz, 6H, 2 × CH3); 13

C NMR (125.8 MHz, CDCl3): δ

= 171.5 (C=O), 170.8 (C=O), 143.3 (C), 139.2 (C), 138.1 (C), 136.6 (C), 129.2 (ArCH),

129.1 (ArCH), 128.5 (ArCH), 128.4 (ArCH), 127.6 (ArCH), 126.5 (C), 45.2 (CH2), 41.6

(CH2), 32.8 (CH2), 30.0 (CH), 28.1 (CH), 22.7 (CH3), 22.3 (CH3); HRMS (EI): calc. for

C25H29NO2 [M]+ 375.2198, found 375.2199; IR (KBr): ν = 3032, 2956, 2867, 1701,

1608 cm-1

.

1-Benzyl-3-(4-butoxyphenyl)-4-isobutyl-1H-pyrrole-2,5-dione (88):

178





1H NMR (399.85, 3H, SiCH3) MHz, CDCl3): δ = 7.46 (app d, 2H, 2 × ArH), 7.34–7.18

(m, 5H, 5 × ArH), 6.90 (app d, 2H, 2 × ArH), 4.67 (s, 2H, CH2Ph), 3.97 (t, J = 6.8 Hz,

2H, OCH2), 2.46 (d, J = 6.8 Hz, 2H, CH2), 2.04–1.94 (m, 1H, CH), 1.84–1.72 (m, 1H,

CH), 1.68–1.62 (m, 2H, CH2), 0.92 (t, J = 6.8 Hz, 3H, CH3), 0.84 (d, J = 6.8 Hz, 6H,

CH2CH(CH3)2); 13

C NMR (100.5 MHz, CDCl3): δ = 172.0 (C=O), 171.2 (C=O), 160.3

(C), 138.2 (C), 137.9 (C), 136.8 (C), 131.1 (ArCH), 128.7 (ArCH), 128.6 (ArCH), 127.8

(ArCH), 121.4 (C), 114.7 (ArCH), 66.5 (CH2), 41.8 (CH2Ph), 38.0 (CH2), 32.8 (CH2),

28.2 (CH), 25.1 (CH), 22.9 (CH3), 22.5 (CH3); MS (EI) (m/z): 405 [M]+ (100), 362 (31),

335 (17), 292 (35), 215 (19), 131 (41); HRMS (EI): calc. for C26H31NO3 [M]+

405.2304, found 405.2302; IR (neat): ν = 3464, 2959, 2872, 1838, 1762 (C=O), 1605,

1513, 1466, 1255, 1171 cm-1

.

1-Benzyl-3-isobutyl-4-(4-(isopentyloxy)phenyl)-1H-pyrrole-2,5-dione (89):





1H NMR (399.85 MHz, CDCl3): δ = 7.46 (app d, 2H, 2 × ArH), 7.34-7.18 (m, 5H, 5 ×

ArH), 6.90 (app d, 2H, 2 × ArH), 4.67 (s, 2H, CH2Ph), 3.97 (t, J = 6.8 Hz, 2H, OCH2),

2.46 (d, J = 6.8 Hz, 2H, CH2CH(CH3)2), 2.04-1.94 (m, 1H, CH),1.84-1.72 (m, 1H, CH),

1.68-1.62 (m, 1H, CH), 0.92 (d, J = 6.8 Hz, 6H, 2 × CH3), 0.84 (d, J = 6.8 Hz, 6H, 2 ×

179

CH3); 13

C NMR (100.5 MHz, CDCl3): δ = 172.0 (C=O), 171.2 (C=O), 160.3 (C), 138.2

(C), 137.9 (C), 136.8 (C), 131.1 (ArCH), 128.7 (ArCH), 128.6 (ArCH), 127.8 (ArCH),

121.4 (C), 114.7 (ArCH), 66.5 (OCH2), 41.8 (CH2Ph), 38.0 (CH2), 32.8 (CH2), 28.2

(CH), 25.1 (CH), 22.9 (CH3), 22.5 (CH3); MS (EI) (m/z): 406 [M + H]+ (28), 405 [M]

+

(100), 362 (31), 335 (17), 292 (35), 215 (19), 131 (41); HRMS (EI): calc. for

C26H31NO3 [M]+ 405.2304, found 405.2302; IR (neat): ν = 3464, 2959, 2872, 1838,

1762 (C=O), 1605, 1513, 1466, 1255, 1171 cm-1

.

3-(4-Aminophenyl)-1-benzyl-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (91):




(178 mg, 32% yield, Rf = 0.78 in 50:50 EtOAc/hexane) as a red oil. (91): 1H NMR

(399.85 MHz, CDCl3): δ = 7.44–7.22 (m, 7H, 7 × ArH), 6.68 (app d, 2H, 2 × ArH), 4.71

(s, 2H, CH2Ph), 3.87 (s, 2H, NH2), 2.51 (d, J = 7.3 Hz, 2H, CH2), 2.10-2.00 (m, 1H),

0.89 (d, J = 6.6 Hz, 6H, (CH3)2); 13

C NMR (100.5 MHz, CDCl3): δ = 172.3 (C=O),

171.5 (C=O), 147.8 (C), 138.0 (C), 136.9 (C), 136.6 (C), 131.1 (ArCH), 128.7 (ArCH),

128.5 (ArCH), 127.7 (ArCH), 119.3 (C), 114.8 (CH2Ph), 41.7 (CH2), 33.0 (CH2), 28.2

(CH), 22.9 (CH3); MS (EI) (m/z): 334 [M]+ (97), 292 (28), 291 (100), 158 (68), 130

(70); HRMS (EI): calc. C21H21N2O2 [M]+ 334.1681, found 334.1677; IR (neat): ν =

3379, 2957, 1696 (C=O), 1604, 1517 cm-1

.

180

3-(4-Acetylphenyl)-1-benzyl-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (92):


(276 mg, 0.99 mmol) and boronic acid 376 (263 mg, 1.20 mmol). The crude material


(302, 84% yield, Rf = 0.60 in 50:50 EtOAc/hexane) as an oil. (92): 1H NMR (500.13

MHz, CDCl3): δ = 8.05 (app d, 2H, 2 ×ArH), 7.66 (app d, 2H, 2 ×ArH), 7.43-7.27 (d,

5H, 5 ×ArH), 4.78 (s, 2H, CH2Ph), 2.64 (s, 3H, C(CH3)=O), 2.57 (d, 2H, J = 7.5 Hz,

CH2), 2.12-2.04 (m, 1H, CH), 0.90 (d, J = 6.5 Hz, 6H, (CH3)2); 13

C NMR (125.8 MHz,

CDCl3): δ = 197.2 (C=O), 170.9 (C=O), 170.1 (C=O), 141.8 (C), 137.3 (C), 137.1 (C),

136.3 (C), 133.5 (C), 129.5 (ArCH), 128.6 (ArCH), 128.4 (ArCH), 128.3 (ArCH), 127.8

(ArCH), 41.8 (CH2Ph), 32.9 (CH2), 28.2 (CH), 26.5 (CH), 22.6 (CH3),; HRMS (EI):

calc. for C23H23NO3 [M]+ 361.1678, found 361.1667; IR (neat): ν = 2958, 2869, 1767,

1704, 1687, 1605, 1402 cm-1

.

1-Benzyl-3-(4-hydroxyphenyl)-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (85):

AlCl3 (26 mg, 0.19 mmol) was added in one portion to a magnetically stirred mixture of

1-benzyl-3-isobutyl-4-(4-isopropoxyphenyl)pyrrolidine-2,5-dione 78 (48 mg, 0.13

mmol) in CH2Cl2 (0.5 mL)and stirred at room temperature under an atmosphere of

argon gas for 16 hours. After this time period, the reaction mixture was quenched with

37% w/w aq NH4Cl. The aqueous layer was then extracted with EtOAc (4 × 20 mL), the

combined organic fractions were dried (Na2SO4), filtered, and concentrated under

181

reduced pressure. The crude material was subjected to column chromatography to give

phenol 85 (1.3 g, 66% yield) as a dark yellow oil. The spectroscopic data for 85

matched that reported previously.

General procedure for the preparation of 3,4-substituted maleic anhydrides:

A mixture of the desired benzylmaleimide (1 mmol), MeOH (250 µL), THF (500 µL),

and KOH (6 mmol in 500 µL H2O) was stirred at reflux for 18 hours. After this time,

the reaction mixture was concentrated under reduced pressure to remove the MeOH and

THF. The reaction mixture was then diluted with 0.5 M aq HCl (2 mL) and EtOAc

(5 mL), and the aqueous and organic layers were separated. The aqueous layer was

extracted further with EtOAc (2 × 5 mL). Then the combined organic extracts were

dried (Na2SO4), filtered, and concentrated under reduced pressure to give a crude oil.

The crude material was subjected to column chromatography to give the desired maleic

anhydride.

3-(2-Methylpropyl)-4-phenylfuran-2,5-dione (97):

The general procedure for the preparation of 3,4-disubstituted maleic anhydrides was

followed using 84 (120 mg, 0.38 mmol). The crude material was subjected to column

chromatography (5:95 EtOAc/hexane) to give compound 97 (33 mg, 73% yield, Rf =

0.50 in 10:90 EtOAc/hexane) as a pale yellow fluorescent oil. (97): 1H NMR (399.85

MHz, CDCl3): δ = 7.60–7.56 (m, 2H, 2 × ArH), 7.53–7.49 (m, 3H, 3 × ArH), 2.60 (d, J

= 7.5 Hz, CH2), 2.12 (m, 1H, CH), 0.93 (d, J = 6.8 Hz, 6H, 2 × CH3); 13

C NMR (100.5

MHz, CDCl3): δ = 166.1 (C=O), 165.1 (C=O), 142.8 (C), 141.1 (C), 130.9 (ArCH),s

129.4 (ArCH), 129.1 (ArCH), 127.6 (C), 33.7 (CH2), 28.1 (CH), 22.7 (CH3); MS (EI)

(m/z): 231 (20), 230 [M]+ (83), 188 (12), 115 (87); HRMS (EI): calc. C14H14O3 [M]

+

230.0943, found 230.0944; IR (neat): ν = 2960, 1842, 1764 (C=O), 1705, 1233, 931,

902, 700 cm-1

.

182

3-(2-Methylpropyl)-4-[4-(propan-2-yloxy)phenyl]furan-2,5-dione (98):




0.53 in 20:80 EtOAc/hexane) as a fluorescent yellow oil. (98): 1H NMR (399.85 MHz,

CDCl3): δ = 7.61 (app d, 2H, 2 × ArH), 6.98 (app d, 2 × ArH), 4.63 (m, 1H, OCH), 2.59

(d, J = 7.6 Hz, 2H, CH2), 2.12 (m, 1H, CH), 1.37 (d, J = 6.0 Hz, 6H, 2 × CH3), 0.94 (d,

J = 6.4 Hz, 6H, 2 × CH3); 13

C NMR (100.5 MHz, CDCl3): δ = 166.6 (C=O), 165.6

(C=O), 160.3 (C), 140.4 (C), 139.8 (C), 131.3 (ArCH), 119.8 (C), 116.0 (ArCH), 70.3

(CH), 33.8 (CH2), 28.1 (CH), 22.8 (CH3), 22.1 (CH3); MS (EI) (m/z): 288 [M]+ (41),

246 (70), 218 (29), 204 (100), 176 (76), 131 (44); HRMS (EI): calc. C17H20O4 [M]+

288.1362, found 288.1363; IR (neat): ν = 2962, 1837, 1761, 1603, 1510 cm-1

.

3-(4-Hydroxyphenyl)-4-(2-methylpropyl)furan-2,5-dione (99):




0.14 in 10:90 EtOAc/hexane) as a yellow oil. (99): 1H NMR (399.85 MHz, CDCl3): δ =

7.56 (app d, 2H, 2 × ArH), 6.97 (app d, 2H, 2 × ArH), 2.58 (d, J = 7.0 Hz, 2H; CH2),

2.10 (m, 1H, CH), 0.93 (d, J = 6.5 Hz, 6H, (CH3)2); 13


166.7 (C=O), 165.8 (C=O), 158.5 (C), 140.5 (C), 140.1 (C), 131.4 (ArCH), 119.9 (C),

183

116.2 (ArCH), 33.7 (CH2), 28.0 (CH), 22.7 (CH3); MS (EI) (m/z): 246 [M]+ (74), 218

(24), 204 (84), 176 (100), 131 (62); HRMS (EI): calc. C14H14O4 [M]+ 246.0892, found

246.0890; IR (neat): ν = 3433 (OH), 2961, 1760 (C=O), 1607, 1515 cm-1

.

3-(2-Methylpropyl)-4-[4-(2-methylpropyl)phenyl]furan-2,5-dione (100):





CDCl3): δ = 7.46 (app d, 2H, 2 × ArH), 7.20 (app d, 2H, 2 × ArH), 2.52 (d, J = 7.2 Hz,

2H, CH2), 2.46 (d, J = 7.2 Hz, 2H, CH2), 2.05 (m, 1H, CH), 1.84 (m, 1H, CH), 0.87–

0.84 (m, 12H, 4 × CH3); 13

C NMR (100.5 MHz, CDCl3): δ = 166.3 (C=O), 165.3

(C=O), 145.3 (C), 141.7 (C), 140.9 (C), 129.8 (ArCH), 129.2 (ArCH), 125.1 (C), 45.4

(CH2), 33.7 (CH2), 30.2 (CH), 28.1 (CH), 22.8 (CH3), 22.5 (CH3); MS (EI) (m/z): 286

[M]+ (53), 244 (100), 201 (33), 173 (44), 128 (31); HRMS (EI): calc. C18H22O3 [M]

+

286.1569, found 286.1569; IR (neat): ν = 2959, 1765 (C=O), 1465, 1234, 928 cm-1

.

3-[4-(3-Methylbutoxy)phenyl]-4-(2-methylpropyl)furan-2,5-dione (101):




184


CDCl3): δ = 7.32 (app d, 2H, 2 × ArH); 7.00 (app d, 2H, 2 × ArH); 4.05 (t, J = 6.4 Hz,

2H, CH2); 2.59 (d, J = 7.6 Hz, 2H, CH2); 2.12 (m, 1H, CH), 1.85 (m, 1H, CH), 1.73–

1.68 (m, 2H, CH2), 0.98 (d, J = 6.8 Hz, 6H, 2 × CH3), 0.94 (d, J = 6.4 Hz, 6H, 2 × CH3);

13C NMR (100.5 MHz, CDCl3): δ = 166.5 (C=O), 165.6 (C=O), 161.4 (C), 140.4 (C),

139.9 (C), 132.7 (C), 131.3 (ArCH), 119.9 (C), 115.1 (ArCH), 66.8 (CH2), 33.7 (CH2),

28.1 (CH), 25.2 (CH), 22.8 (CH3), 22.7 (CH3); MS (EI) (m/z): 317 (19), 316 [M]+ (96),

303 (16), 274 (10), 246 (68), 204 (98), 176 (54), 131 (55); HRMS (EI): calc. C19H24O4

[M]+ 316.1675, found 316.1679; IR (neat): ν = 3447, 2957, 1702 (C=O), 1512, 1433,

1400, 1351, 1251 cm-1

.

3-(4-Butylphenyl)-4-(2-methylpropyl)furan-2,5-dione (102):



chromatography (5:95 EtOAc/hexane) to give compound 102 (43 mg, 63% yield) as a

fluorescent yellow oil. (102): 1H NMR (399.85 MHz, CDCl3): δ = 7.55 (app d, 2H, 2 ×

ArH), 7.34 (app d, 2H, 2 × ArH), 2.67 (t, J = 7.6 Hz, 2H, CH2), 2.60 (d, J = 7.4 Hz, 2H,

CH2), 2.17 (m, 1H, CH), 1.68-1.58 (m, 2H, CH2), 1.44-1.32 (m, 2H, CH2), 0.97-0.89

(m, 9H, 3 × CH3); 13


146.5 (C), 141.6 (C), 141.0 (C), 129.4 (ArCH), 129.2 (CH), 35.8 (CH2), 33.8 (CH), 33.5

(CH2), 28.2 (CH2), 22.9 (CH3), 22.6 (CH2), 14.2 (CH3); MS (EI) (m/z): 287 [M]+ (56),

244 (100), 216 (38), 173 (21), 171 (21), 128 (31); HRMS (EI): calc. C18H23O3 [M]+

286.1569, found 286.1561; IR (neat): ν = 2959, 1766, 1234, 928 cm-1

.

185

3-(4-Aminophenyl)-4-(2-methylpropyl)furan-2,5-dione (103):




0.60 in 50:50 EtOAc/hexane) as a red oil. (103): 1H NMR (399.85 MHz, CDCl3): δ =

7.55 (app d, 2H, 2 × ArH), 6.75 (app d, 2H, 2 × ArH), 4.06 (s, 2H, NH2), 2.58 (d, J =

7.2 Hz, 2H, CH2), 2.11 (m, 1H, CH), 0.95 (d, J = 6.4 Hz, 6H, 2 × CH3); 13

C NMR

(100.5 MHz, CDCl3): δ = 166.9 (C=O), 165.9 (C=O), 149.1 (C), 140.3 (C), 137.7 (C),

131.4 (ArCH), 117.7 (C), 114.9 (ArCH), 33.8 (CH2), 28.0 (CH), 22.8 (CH3); MS (EI)

(m/z): 245 [M]+ (79), 202 (54), 175 (41), 158 (27), 130 (100); HRMS (EI): calc.

C14H15NO3 [M]+ 245.1052, found 245.1047; IR (neat): ν = 3390 (NH2), 2960, 1823,

1755 (C=O), 1601, 1519 cm-1

.

3-[4-(Dimethylamino)phenyl]-4-(2-methylpropyl)furan-2,5-dione (104):




0.48 in 20:80 EtOAc/hexane) as a red solid. (104): 1H NMR (399.85 MHz, CDCl3): δ =

7.69 (app d, 2H, 2 × ArH), 6.74 (app d, 2H, 2 × ArH), 3.07 (s, 6H, N(CH3)2), 2.6 (d, J =

7.0 Hz, 2H, CH2), 2.13 (m, J, 1H, CH), 0.97 (d, J = 6.5 Hz, 2 × CH3); 13

C NMR (100.5

MHz, CDCl3): δ = 167.2 (C=O), 166.2 (C=O), 151.8 (C), 140.0 (C), 135.5 (C), 131.2

186

(ArCH), 115.3, 111.7 (ArCH), 40.1 (N(CH3)2), 33.8 (CH2), 27.9 (CH), 22.8 (CH3); MS

(EI) (m/z): 273 [M]+ (93), 230 (100), 186 (27), 158 (86); HRMS (EI): calc. C16H19NO3

[M]+ 273.1365, found 273.1362; IR (neat): ν = 2958, 2926, 1753 (C=O), 1603, 1528

cm-1

.

3-[4-(Benzyloxy)phenyl]-4-(2-methylpropyl)furan-2,5-dione (105):





CDCl3): δ = 7.63 (app d, 2 × ArH). 7.46–7.36 (m, 5H, 5 × ArH), 7.09 (app d, 2 × ArH),

5.14 (s, 2H, CH2Ph), 2.60 (d, J = 7.2 Hz, 2H, CH2), 2.13 (m, 1H, CH), 0.95 (d, J = 6.4

Hz, 6H, 2 × CH3); 13


160.9 (C), 140.3 (C), 140.2 (C), 136.3 (C), 131.3 (ArCH), 128.9 (ArCH), 128.4 (ArCH),

127.6 (ArCH), 120.4 (C), 115.5 (ArCH), 70.3 (CH2Ph), 33.7 (CH2), 28.1 (CH), 28.0

(CH3); MS (EI) (m/z): 337 (21), 336 [M]+ (100), 149 (18); HRMS (EI): calc. C21H20O4

[M]+ 336.1362, found 336.1372; IR (neat): ν = 2961, 2871, 1761 (C=O), 1604 cm

-1.

General procedure for the preparation of 3,4-disubstituted maleimides:

A mixture of the desired maleic anhydride (1 mmol) and urea (2 mmol) was stirred at

140°C for 2 hours. After this time, the reaction mixture was cooled to room

temperature, and diluted with EtOAc (10 mL) and H2O (10 mL). The aqueous and

organic layers were separated, and the aqueous layer was extracted further with EtOAc

(3 × 10 mL). The combined organic extracts were dried (Na2SO4), filtered, and

concentrated under reduced pressure to give a crude oil. The crude material was

subjected to column chromatography to give the desired maleimide.

187

3-(2-Methylpropyl)-4-phenyl-1H -pyrrole-2,5-dione (109):

The general procedure for the preparation of 3,4-disubstituted maleimides was followed

using 97 (21 mg, 0.09 mmol). The crude material was subjected to column


0.33 in 10:90 EtOAc/hexane) as a colourless oil. (109): 1H NMR (399.85 MHz,

CDCl3): δ = 8.18 (s, 1H, NH), 7.44-7.18 (m, 5H, 5 × ArH), 2.43 (d, J = 7.2 Hz, CH2),

1.97 (m, 1H, CH), 0.80 (d, J = 7.0 Hz, 3H, CH3); 13


172.1 (C=O), 171.4 (C=O), 141.3 (C), 139.4 (C), 129.7 (ArCH), 129.4 (ArCH), 128.9

(C), 128.7 (ArCH), 32.8 (CH2), 28.2 (CH), 22.8 (CH3); MS (EI) (m/z): 229 [M]+ (100),

188 (12), 187 (99), 115 (38); HRMS (EI): calc. C14H15NO2 [M]+ 229.1103, found

229.1102; IR (neat): ν = 3290 (NH), 2958, 2870, 1772 (C=O), 1718 cm-1

.

3-(2-Methylpropyl)-4-[4-(propan-2-yloxy)phenyl]-1H-pyrrole-2,5-dione (110):





CDCl3): δ = 8.10 (s, 1H, NH), 7.50 (app d, 2H, 2 × ArH), 6.95 (app d, 2H, 2 × ArH),

4.61 (m, 1H, CH), 2.50 (d, J = 7.0 Hz, 2H, CH2), 2.05 (m, 1H, CH), 1.36 (d, J = 6.0 Hz,

6H, 2 × CH3), 0.89 (d, J=6.5 Hz, 6H, 2 × CH3); 13


172.4 (C= O), 171.7 (C=O), 159.2 (C), 139.1 (C), 138.8 (C), 131.1 (ArCH), 121.0 (C),

115.8 (ArCH), 70.1 (CH), 32.9 (CH2), 28.2 (CH), 22.8 (CH3), 22.1 (CH3); MS (EI)

(m/z): 287 [M]+ (35), 245 (84), 203 (100), 159 (13), 131 (33); HRMS (EI): calc.

188

C17H21NO3 [M]+ 287.1521, found 287.1516; IR (neat): ν = 3280 (NH), 2960, 1709

(C=O), 1604, 1509 cm-1

.

3-(2-Methylpropyl)-4-[4-(2-methylpropyl)phenyl]-1H-pyrrole-2,5-dione (112):




fluorescent yellow oil. (112): 1H NMR (399.85 MHz, CDCl3): δ = 8.30 (s, 1H, NH),

7.46 (app d, 2H, 2 × ArH), 7.25 (app d, 2H, 2 × ArH), 2.53 (d, J = 7.0 Hz, 2H, CH2),

2.53 (d, J = 7.5 Hz, 2H, CH2), 2.08 (m, 1H, CH), 1.92 (m, 1H, CH), 0.93 (d, J = 7.0 Hz,

6H, 2 × CH3), 0.91 (d, J = 6.5 Hz, 6H, 2 × CH3); 13


172.3 (C=O), 171.6 (C=O), 143.7 (C), 140.4 (C), 139.3 (C), 129.4 (ArCH), 129.4

(ArCH), 126.3 (C), 45.4 (CH2), 32.8 (CH), 30.2 (CH2), 28.3 (CH), 22.8 (CH3), 22.5

(CH3); MS (EI) (m/z): 285 [M]+ (100), 243 (64), 228 (60), 201 (29), 200 (73); HRMS

(EI): calc. C18H23NO2 [M]+ 285.1729, found 285.1736; IR (neat): ν = 3292 (NH), 2957,

2870, 1771 (C=O), 1722, 1714 cm-1

.

3-[4-(3-Methylbutoxy)phenyl]-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (113):




189


CDCl3): δ = 7.73 (s, 1H, NH), 7.50 (app d, 2H, 2 × ArH), 6.97 (app d, 2H, 2 × ArH),

4.03 (t, J = 6.6 Hz, 2H, CH2), 2.50 (d, J = 7.5 Hz, 2H, CH2), 2.05 (m, J = 6.6 Hz, 1H,

CH), 1.85 (m, 1H, CH), 1.73–1.66 (m, 2H, CH2), 0.97 (d, J = 6.6 Hz, 6H, 2 × CH3),

0.90 (d, J = 6.6 Hz, 6H, 2 × CH3); 13

C NMR (100.5 MHz, CDCl3): δ = 172.1 (C=O),

171.5 (C=O), 160.4 (C), 139.1 (C), 138.9 (C), 131.1 (ArCH), 121.2 (C), 114.8 (ArCH),

66.6 (CH2), 38.0 (CH2), 32.9 (CH2), 28.2 (CH), 25.2 (CH), 22.8 (CH3), 22.7 (CH3); MS

(EI) (m/z): 316 [M]+ (21), 315 (96), 245 (79), 203 (100), 202 (45), 131 (31); HRMS

(EI): calc. C19H25NO3 [M]+ 315.1834, found 315.1835; IR (neat): ν = 3292 (NH), 2956,

2869, 1707 (C=O), 1605, 1511 cm-1

.

3-(4-Butylphenyl)-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (114):




fluorescent yellow oil. (114): 1H NMR (399.85 MHz, CDCl3): δ = 7.49 (s, 1H, NH),

7.44 (app d, 2H, 2 × ArH), 7.27 (app d, 2 × ArH), 2.65 (t, J =7.5 Hz, 2H, CH2), 2.51 (d,

J = 7.5 Hz, 2H, CH2), 2.06 (m, 1H, CH(CH3)2), 1.66–1.58 (m, 2H, CH2), 1.41–1.33 (m,

2H, CH2), 0.94 (t, J = 7.5 Hz, 2H, CH2) 0.90 (d, J =7.0 Hz, 6H, 2 × CH3); 13

C NMR

(100.5 MHz, CDCl3): δ = 172.0 (C=O), 171.2 (C=O), 145.0 (C), 140.5 (C), 139.4 (C),

129.4 (ArCH), 128.8 (ArCH), 126.2 (C), 35.7 (CH2), 33.5 (CH), 32.9 (CH2), 28.3

(CH2), 22.8 (CH3), 22.5 (CH2), 14.1 (CH3); MS (EI) (m/z): 285 [M]+ (100), 243 (76),

228 (64), 200 (46), 186 (26); HRMS (EI): calc. C18H23NO2 [M]+ 285.1729, found

285.1725; IR (neat): ν = 3271 (NH), 2958, 2928, 2870, 1708, 1608; 1414 cm-1

.

190

3-[4-(Dimethylamino)phenyl]-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (115):




0.18 in 10:90 EtOAc/hexane) as a red solid. (115): 1H NMR (399.85 MHz, CDCl3): δ =

7.61 (s, 1H, NH), 7.56 (app d, 2H, 2 × ArH), 6.75 (app d, 2 × ArH), 3.03 (s, 6H,

N(CH3)2), 2.52 (d, J = 7.5 Hz, 2H, CH2), 2.07 (m, 1H, CH), 0.92 (d, J = 7.0 Hz, 6H, 2 ×

CH3); 13

C NMR (100.5 MHz, CDCl3): δ = 172.6 (C=O), 171.9 (C=O), 151.1 (C), 138.9

(C), 136.3 (C), 131.0 (ArCH), 116.8 (C), 111.9 (ArCH), 40.2 (N(CH3)2), 33.0 (CH2),

28.1 (CH), 22.9 (CH3); MS (EI) (m/z): 272 [M]+ (71), 229 (100), 186 (55), 158 (30);

HRMS (EI): calc. C16H20N2O2 [M]+ 272.1525, found 272.1519; IR (neat): ν = 3216

(NH), 2952, 2341, 1763 (C=O), 1701 (C=O), 1608, 1528 cm-1

.

3-[4-(Benzyl oxy)phenyl]-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (116):





CDCl3): δ = 7.52 (app d, 2H, 2 × ArH), 7.46–7.25 (m, 5H, 5 × ArH), 7.29 (s, 1H; NH),

7.06 (app d, 2 × ArH), 5.12 (s, 2H, CH2Ph), 2.33 (d, 7.6 Hz, 2H, CH2), 2.12–2.00 (m,

1H, CH), 0.90 (d, J = 6.8 Hz, 6H, 2 × CH3); 13

C NMR (100.5 MHz, CDCl3): δ = 171.7

191

(C=O), 171.1 (C=O), 160.1 (C), 139.5 (C), 138.8 (C), 136.6 (C), 131.1 (CH-Ar), 128.8

(ArCH), 128.3 (ArCH), 127.6 (ArCH), 121.7 (C), 115.2 (ArCH), 70.2 (CH2Ph), 33.0

(CH2), 28.3 (CH), 22.9 (CH3); MS (EI) (m/z): 336 (30), 335 (99), 205 (44), 171 (19),

129 (30); HRMS (EI): calc. C21H21NO3 [M]+ 335.1521, found 335.1524; IR (neat): ν =

3303 (NH), 2959, 1708 (C=O), 1604, 1510, 1251, 1176, 1023 cm-1

.

1-Hydroxy-3-(4-hydroxyphenyl)-4-(2-methylpropyl)-1H-pyrrole-2,5-dione (35):

A mixture of maleic anhydride 34 (130 mg, 0.53 mmol) and hydroxylamine

hydrochloride (73 mg, 1.0 mmol) was dissolved in ethanol (3 mL) and the pH of the

mixture was adjusted to 11 with 11% w/w aq NaOH. The solution was refluxed for 3 h

and then the precipitate was removed by filtration. The solvent was evaporated to

dryness and the residue was dissolved in water and acidified to pH 5 with 2 M aq HCl.

The crude material was subjected to column chromatography (5:95 EtOAc/hexane) to

give compound 35 (99 mg, 72% yield, Rf = 0.41 in 20:80 EtOAc/hexane) as a yellow

oil. (35): 1H NMR (399.85 MHz, CDCl3): δ = 8.98 (s, 1H; NOH), 7.56 (app d, 2H,

ArH), 7.00 (app d, 2H, ArH), 2.56 (d, J = 7.2 Hz, 2H, CH2), 2.06 (m, 1H, CH), 0.91 (d,

J = 6.6 Hz, 6H, (CH3)2); 13

C NMR (100.5 MHz, CDCl3): δ = 169.0 (C=O), 168.2

(C=O), 159.7 (C), 136.5 (C), 135.9 (C), 132.1 (ArCH), 121.3 (C), 116.3 (ArCH), 33.4

(CH2), 28.6 (CH), 22.9 (CH3); HRMS (EI): calc. C14H15NO4 [M]+ 264.1001, found

261.1000; IR (neat): ν = 3367 (OH), 2926, 1714, 1607, 1514 cm-1

.

1-Benzyl-3,4-di(thiophen-2-yl)-1H-pyrrole-2,5-dione (124):

192

The general procedure for the Suzuki reaction was followed using dichloromaleimide

46 (120 mg, 0.47 mmol) and boronic ester 377 (207 mg, 0.99 mmol). The crude

material was subjected to column chromatography (5:95 EtOAc/hexane) to give

compound 124 as an orange solid (50 mg, 30% yield). (124): m.p. 130-132°C; 1H

NMR (399.85 MHz, CDCl3): δ = 7.82 (app dd, ArH), 7.57 (app dd, 2H, ArH), 7.46-7.42

(m, 2H, 2 × ArH), 7.37-7.28 (m, 3H, 3 × ArH), 7.12 (app dd, 2H, 2 × ArH), 4.79 (s, 2H,

CH2Ph); 13

C NMR (100.5 MHz, CDCl3): δ = 170.0 (C=O), 136.3, 131.5, 131.1, 129.8,

128.9, 128.8, 128.1, 127.7, 42.3 (CH2Ph); MS (EI) (m/z): 351 [M]+ (100), 323 (13), 246

(12), 191 (15), 190 (38); HRMS (EI): calc. C19H13NO2S2 [M]+ 351.0388, found

351.0386; IR (KBr): ν = 2925, 1765, 1700 (C=O), 1432, 1401, 699 cm-1

.

1-Benzyl-3,4-bis(4-(dimethylamino)phenyl)-1H-pyrrole-2,5-dione (125):




compound 125 as a dark red solid (22 mg, 6% yield, Rf = 0.24 in 30:70 EtOAc/hexane).

(125): m.p. 191-193°C; 1H NMR (399.85 MHz, CDCl3): δ = 7.45-7.38 (m, 4H, 4×

ArH), 7.38-7.36 (m, 2H, 2× ArH), 7.26-7.18 (m, 4H, 4 × ArH), 6.57 (app d, 4H, 4×

ArH), 4.69 (s, 2H, CH2Ph), 2.92 (s, 12H, 4× N(CH3)2); 13

C NMR (100.5 MHz, CDCl3):

δ = 171.8 (C=O), 137.2, 131.2, 128.8, 128.7, 127.7, 111.8, 41.7 (CH2Ph), 40.3

(N(CH3)2); HRMS (EI): calc. C27H27N3O2 [M]+ 425.2103, found 425.2107; IR (neat): ν

= 2895, 1695, 1604, 1354, 1196, 818 cm-1

.

193

1-Benzyl-3,4-diphenyl-1H-pyrrole-2,5-dione (126):




compound 126 as a dark red solid (22 mg, 9% yield). (126): 1H NMR (399.85 MHz,

CDCl3): δ = 7.47–7.44 (m, 6H, 6 × ArH), 7.36–7.30 (m, 9H, 9 × ArH), 4.80 (s, 2H,

NCH2); 13

C NMR (100.5 MHz, CDCl3): δ = 170.6 (2 ×C=O), 136.6, 136.3, 130.0,

130.0, 129.0, 128.8, 128.7, 128.7, 128.1, 42.2 (CH2); HRMS (EI): calc. C23H17NO2

[M]+ 339.1259, found 339.1252; IR (neat): ν = 3060, 1701 (C=O), 1433, 1401, 1350,

1075, 692 cm-1

.

1-Benzyl-3,4-bis(4-isopropoxyphenyl)-1H-pyrrole-2,5-dione (127):


46 (184 mg, 0.72 mmol) and boronic ester 71 (307 mg, 1.50 mmol). The crude material


as fluorescent green oil (12 mg, 9% yield). (127): 1H NMR (399.85 MHz, CDCl3): δ

=7.52–7.40 (m, 6H, 6 × ArH), 7.39–7.24 (m, 3H, 3 × ArH), 6.86 (m, 4H, 4 × ArH), 4.81

(s, 2H, NCH2), 4.60 (sept, J = 6.0 Hz, 2H, 2 × CH), 1.37 (d, J = 6.0 Hz, 12H, 4 × CH3);

13C NMR (100.5 MHz, CDCl3): δ = 171.2, 159.3, 136.8, 134.0, 131.6, 128.9, 128.8,

127.8, 121.1, 115.6, 70.0 (2 × CH), 42.0 (CH2), 22.1 (2 × CH3); HRMS (EI): calc.

194

C29H29NO4 [M+] 455.2097, found 455.2109; IR (neat): ν = 3019, 2980, 1700 (C=O),

1251, 1215,

668 cm-1

.

1-Benzyl-3,4-bis(4-acetylphenyl)-1H-pyrrole-2,5-dione (128):




compound 128 as yellow oil (12 mg, 45% yield). (128): 1H NMR (399.85 MHz,

CDCl3): δ = 7.92–7.53 (m, 4H, 4 × ArH), 7.54–7.51 (m, 4H, 4 × ArH), 7.45–7.41 (m,

2H, 2 × ArH), 7.32–7.29 (m, 3H, 3 × ArH), 4.82 (s, 2H, NCH2), 2.60 (s, 6H, 2 × CH3);

13C NMR (100.5 MHz, CDCl3): δ = 197.4, 169.6, 138.0, 136.52, 136.12, 132.8, 130.2,

129.0, 128.9, 128.58, 128.18, 42.4, 26.8; HRMS (EI): calc. C27H21NO4 [M+] 423.1471,

found 423.1465; IR (neat): ν = 3011, 1705 (C=O), 1685 (C=O), 1401, 1,66, 832, 752

cm-1

.

1-Benzyl-3,4-bis(4-hydroxyphenyl)-1H-pyrrole-2,5-dione (129):



195


compound 129 as a yellow oil (30 mg, 46% yield). (129): 1H NMR (399.85 MHz, d6-

acetone): δ = 7.46–7.20 (m, 9H, 9 × ArH), 6.90–6.82 (m, 4H, 4 × ArH), 4.80 (s, 2H,

CH2); 13

C NMR (100.5 MHz, d6-acetone): δ = 171.6, 159.6, 138.2, 134.9, 132.4, 129.3,

128.7, 128.2, 121.4, 116.2, 42.1; HRMS (EI): calc. C23H17NO4 [M+] 371.1158, found

371.0146; IR (neat): ν = 3393, 1693, 1606, 1351, 1172, 838 cm-1

.

196

197


3-(Hydroxymethyl)phenol (175):

Benzaldehyde 181 (11.4 g, 93.0 mmol) was added to a mixture of powdered LiAlH4

(3.50 g, 92.2 mmol) and THF (100 mL) stirring at 0°C, under an atmosphere of argon

gas. The resulting mixture was stirred at 0°C for 1 hour before being quenched with

63% w/w aq KNaC4H4O6.4H2O (50 mL). After two distinct layers formed the reaction

mixture was diluted with EtOAc (100 mL) and the organic and aqueous layers were

separated. The aqueous layer was extracted further with portions of EtOAc (2 × 50 mL)

and then the combined organic layers were dried (MgSO4), and concentrated under

reduced pressure to give alcohol 175 as a white solid (10.83 g, 87% yield, Rf = 0.50 in

50:50 EtOAc/hexane). The product was used without further purification. The

spectroscopic data for compound 175 matched that reported previously in the

literature.378

Phenyliodonium diacetate (182):

Method A:

A mixture of H2O2 (30%, 53.0 mL) and Ac2O (229 mL) was stirred at 40°C for 4 hours.

After this time, iodobenzene (21.0 mL, 38.4 g, 18.8 mmol) was added to this mixture

and it was left to stir at 40°C for 18 hours. After 18 hours, the reaction mixture was

evaporated to 1/4 of the volume under reduced pressure and chilled in an ice bath for 1

hour. The solid that precipitated out was collected by vacuum filtration, and washed

with 5 M aq AcOH (1 × 20 mL) and Et2O (2 × 40 mL) to give PIDA 182 (49 g, 81%

yield) as a white solid The spectroscopic data for compound 182 matched that reported


198

Method B:

Peracetic acid (40%, 93.0 mL) was added drop-wise to a well stirred flask containing

iodobenzene (33.0 mL, 60.4 g, 29.6 mmol) and the mixture was maintained at a

temperature of 30°C. After addition of the peracetic acid, the reaction mixture was

stirred for a further 20 minutes at 30°C, at which time a precipitate formed from the

yellow solution. After this time, the reaction vessel was chilled in an ice bath for 1 hour.

The yellow solid that precipitated out was collected by vacuum filtration and washed

with 5 M aq AcOH (1 × 60 mL), water (3 × 60 mL), and Et2O (2 × 60 mL) to give

iodosobenzene diacetate 182 as a white solid (81.0 g, 85% yield). The spectroscopic

data for compound 182 matched that reported previously in the literature.379

General procedure for phenolic oxidation with PIDA:

Method A:

PIDA (1.1 mmol for para-methoxyphenols or 2.1 mmol, for para-unsubstituted

phenols) was added portion-wise to a magnetically stirred solution of the phenol (1.00

mmol) and A.R. MeOH (1.7 mL) at 0°C, under an atmosphere of argon gas. The

reaction mixture was then stirred at 0°C for 1 hour, followed by stirring at room

temperature for 2 hours. After this time, the reaction mixture was quenched with 9%

w/w aq NaHCO3 (2.5 mL) until the reaction mixture stopped effervescing, then diluted

with EtOAc (4 mL), and immediately transferred to a separating funnel. The organic

and aqueous layers were separated, and the aqueous layer was extracted further with

portions of EtOAc (2 × 4 mL). The combined organic layers were dried (MgSO4),

filtered, and concentrated under reduced pressure to give the crude reaction material.

The crude material was subjected to column chromatography to give the desired

product(s).

Method B:

PIDA (1.1 mmol for para-methoxyphenols or 2.1 mmol, for para-unsubstituted

phenols) was added portion-wise to a magnetically stirred solution of the desired phenol

(1 mmol) and A.R. MeOH (1.7 mL) at 0°C, under an atmosphere of argon gas. The

reaction mixture was then stirred at 0°C for 1 hour, then at room temperature for 2

hours. After this time, the reaction mixture was concentrated under reduced pressure to

remove the MeOH (~30°C) and give a crude oil. The crude material was subjected to

column chromatography to give the desired product(s).

199

Method C:

The desired phenol (1.0 mmol) was added portion-wise to a magnetically stirred

solution of PIDA (1.1 mmol for para-methoxyphenols or 2.10 mmol, for para-

unsubstituted phenols) and A.R. MeOH (1.7 mL) at 0°C, under an atmosphere of argon

gas. The reaction mixture was then stirred at 0°C for 1 hour, followed by stirring at

room temperature for 2 hours. After this time, the reaction mixture was quenched with

22% w/w aq Na2CO3 (2 mL), diluted with EtOAc (2 mL), and stirred at room

temperature for 10 minutes. The reaction mixture was then decanted into a separating

funnel. The copious amount of white precipitate that formed was rinsed twice with

EtOAc (1 mL), and the EtOAc used for rinsing was also added to the separating funnel.

The organic and aqueous layers were separated, and the aqueous layer was extracted

further with portions of EtOAc (2 × 2 mL). The combined organic layers were dried

(MgSO4), filtered, and concentrated under reduced pressure to give the crude reaction

material. The crude material was subjected to column chromatography to give the

desired product(s).

3-Hydroxy-2,6-dimethoxybenzaldehyde (183):

The general procedure for phenolic oxidation with PIDA (method C) was followed

using 175 (2.75 g, 22.2 mmol). The crude material was subjected to column

chromatography (10:90 → 20:80 EtOAc/hexane) to give phenol 183 as a yellow solid

(1.09 g, 27% yield, Rf = 0.57 in 50:50 EtOAc/hexane). (183): m.p. 93-94°C; 1H NMR

(600.13 MHz, CDCl3): δ = 10.45 (s, 1H, CHO), 7.16 (app d, 1H, ArH-4), 6.67 (app d,

1H, ArH-5), 5.69 (s, 1H, OH), 3.90 (s, 3H, CH3-2'), 3.86 (s, 3H, CH3-6'); 13

C NMR

(150.9 MHz, CDCl3): δ = 189.4 (CHO), 156.3 (ArC-6), 147.4 (ArC-2), 143.4 (ArC-3),

121.6 (ArCH-4), 118.4 (ArC-1), 107.8 (ArCH-5), 62.9 (OCH3-2'), 56.5 (OCH3-6').

HRMS (EI): calc. for C9H10O4 [M]+ 182.0579, found 182.0572; IR (KBr): ν = 3420

(OH), 2944, 2885, 2840, 2789, 2191, 1870, 1681, 1603, 1500, 1488, 1465 cm-1

.

200

5-Hydroxy-2-methoxybenzaldehyde (184); 5-(hydroxymethyl)-6,6-dimethoxycyclo

hexa-2,4-dien-1-one (185); 3-(hydroxymethyl)-4,4-dimethoxycyclo hexa-2,5-dien-1-

one (172):

The general procedure for phenolic oxidation with PIDA (method A) was followed


chromatography (10:90 → 30:50 EtOAc/hexane) to give benzaldehyde 184 (163 mg,

3% yield, Rf = 0.61 in 50:50 EtOAc/hexane), meta-benzoquinone ketal 185 (199 mg,

4% yield, Rf = 0.38 in 50:50 EtOAc/hexane) as a yellow solid, and para-benzoquinone

ketal 172 (3.12 g, 53% yield, Rf = 0.33 in 50:50 EtOAc/hexane). The spectroscopic data

for benzaldehyde 184 and benzoquinone ketal 172 matched that reported previously.

(185): 1H NMR (600.13 MHz, CDCl3): δ = 6.93 (dd, J = 6.6 and 10.2 Hz, 1H,

CH=CH), 6.47-6.45 (m, 1H, CH=CH), 5.97 (dd, J = 1.2 and 10.2 Hz, 1H, CH=CH),

4.31 (d, J = 1.2 Hz, 2H, CH2OH), 3.19 (s, 6H, 2 ×OCH3); 13

C NMR (150.9 MHz,

CDCl3): δ = 197.0 (C=O), 150.5 (C), 140.6 (C=CH), 125.3 (C=CH), 122.2 (C=CH),

94.0 (C), 60.8 (CH2), 51.0 (CH3); HRMS (FAB): calc. for C9H13O4 [M + H]+ 185.0814,

found 185.0804; IR (neat): ν = 3468 (OH), 3000, 2954, 2844, 1673, 1651, 1579, 1442,

1407, 1375, 1316, 1263, 1220 1181, 1109, 1031, 1010, 995 cm-1

. (172): 1H NMR

(500.13 MHz, CDCl3): δ = 6.78 (d, J = 10.3 Hz, 1H, CH=CH-5), 6.52-6.51 (m, 1H,

C=CH-2), 6.42 (dd, J = 2.2 and 10.3 Hz, 1H, CH=CH-6), 4.41 (dd, J = 1.8 and 5.9 Hz,

2H, CH2OH), 3.27 (s, 6H, 2 × OCH3), 2.29 (t, J = 5.9 Hz, 1H, CH2OH); 13

C NMR

(125.8 MHz, CDCl3): δ = 185.3 (C=O), 158.2 (CH=C-3), 143.5 (CH=CH-5), 132.2

(CH=CH-6), 126.3 (C=CH-2), 95.3 (C-4), 59.4 (CH2OH), 51.1 (2× OCH3); HRMS

(FAB): calc. for C9H13O4 [M + H]+ 185.0814, found 185.0804; IR (neat): ν = 3447

(broad, OH), 2943, 2834, 1736, 1678 (C=O), 1643 (C=C) cm-1

.

201

5-Hydroxy-2-methoxybenzaldehyde (184):

Sulfuric acid was cooled to 0°C in an ice bath (58 mL) and then added to a flask

containing dimethoxybenzaldehyde 193 (10.0 g, 65.5 mmol). The resulting mixture was

stirred at 0°C for 15 minutes before being heated at 54°C in an oil bath, under argon

gas, for 48 hours. After this time, the reaction mixture was cooled to room temperature

and then carefully poured onto crushed ice (125 mL). A mixture of Et2O/hexane (50:50)

was added (200 mL), the mixture was gently swirled, and the organic and aqueous

layers were separated. The aqueous layer was then extracted further with portions of

Et2O/hexane (50:50) (2 × 200 mL). The combined organic layers were washed with

brine (125 mL), filtered through a plug of silica to dry, and concentrated under reduced

pressure to give a crude solid. The crude solid was re-dissolved in Et2O (100 mL) and

extracted with 110 mL of 5 % aq NaOH. The aqueous and organic layers were

separated, and the aqueous layer was washed with another portion of Et2O (100 mL).

The aqueous layer was then acidified with 2 M aq HCl (~ pH 2) and extracted with Et2O

once more (2 × 100 mL). The ether layer was dried (MgSO4) and concentrated under

reduced pressure to give a crude solid. The crude solid was subjected to flash column

chromatography on silica gel (5:95 → 20:80 EtOAc/hexane) to give phenol 184 as a

yellow solid (3.94 g, 43% yield, Rf = 0.28 in 20:80 EtOAc/hexane). The spectroscopic

data for 184 matched that reported previously in the literature.287

2-Hydroxy-5-methoxybenzaldehyde (194); 5-hydroxy-2-methoxybenzaldehyde

(184):

A mixture of benzaldehyde 193 (1.28 g, 7.70 mmol) and HBr (48%, 85 mL) were

stirred at 90°C for 18 hours, under an atmosphere of argon gas. After this time, the

202

reaction mixture was cooled to room temperature and extracted with Et2O (3 × 85 mL).

The combined ether layers were washed with brine, dried (MgSO4), filtered, and

concentrated under reduced pressure to give a crude oil. The crude oil was subjected to

flash column chromatography on silica gel (2:98 → 20:80 EtOAc/hexane). First to elute

was phenol 194 (82 mg, 7% yield, Rf = 0.64 in 20:80 EtOAc/hexane). Next to elute was

dimethoxybenzaldehyde 193 (79 mg g, 6% yield, Rf = 0.55 in 20:80 EtOAc/hexane).

Last to elute was phenol 184 (199 mg, 17% yield, Rf = 0.28 in 20:80 EtOAc/hexane).

The spectroscopic data for compounds 194 and 184 matched that reported previously in

the literature.380,381

3-(Hydroxymethyl)-4-methoxyphenol (190):

Benzaldehyde 184 (3.67 g, 24.1 mmol) in THF (30 mL) was added carefully drop-wise

to a mixture of powdered LiAlH4 (1.06 g, 27.9 mmol) in THF (70 mL) stirring at 0°C

under an atmosphere of argon gas. The resulting mixture was stirred at 0°C for 1 hour

before being quenched with 63% w/w aq KNaC4H4O6.4H2O (50 mL). After two distinct

layers formed, the reaction mixture was diluted with EtOAc (70 mL), and the organic

and aqueous layers were separated. The aqueous layer was extracted further with

portions of EtOAc (2 × 50 mL) and then the combined organic layers were dried

(MgSO4), and concentrated under reduced pressure to give a pink oil. The crude oil was


benzylic alcohol 190 as a as a pale pink solid (3.38 g, 91% yield, Rf = 0.38 in 50:50

EtOAc/hexane). (190): 1H NMR (600.13 MHz, MeOD): δ = 6.86 (app d, 1H, ArH-2),

6.73 (app d, 1H, ArH-5), 6.64 (app dd, 1H, ArH-6), 4.55 (s, 2H, CH2OH), 3.71 (s, 3H,

OCH3); 13

C NMR (150.9 MHz, MeOD): δ = 151.9 (ArC-1), 151.6 (ArC-4), 131.7

(ArC-3), 116.1 (ArCH-2), 115.0 (Ar-CH-6), 112.5 (ArCH-5), 60.3 (CH2OH), 56.3

(OCH3); HRMS (EI): calc. for C8H10O3 [M]+ 154.0630, found 154.0634; IR (neat): ν =

3337 (broad, OH), 2945, 2836, 2492, 1994, 1838, 1598, 1504 cm-1

.

203

5-Hydroxy-2-methoxybenzaldehyde (184); 3-(hydroxymethyl)-4,4-dimethoxycyclo

hexa-2,5-dien-1-one (172):



chromatography (20:80 → 40:60 EtOAc/hexane) to give benzaldehyde 184 (488 mg,

17% yield, Rf = 0.61 in 50:50 EtOAc/hexane) as a yellow solid, and para-benzoquinone

ketal 172 (2.20 g, 64% yield, Rf = 0.33 in 50:50 EtOAc/hexane) as a yellow oil. The

spectroscopic data for benzaldehyde 184 and ketal 172 matched that reported

previously.

(2,5-Dimethoxyphenyl)methanol (195):

Benzaldehyde 193 (2.10 g, 12.6 mmol) was added to a mixture of powdered LiAlH4

(575 mg, 15.2 mmol) and THF (100 mL) stirring at 0°C under an atmosphere of argon

gas. The resulting mixture was stirred at 0°C for 1 hour before being quenched with

63% w/w aq KNaC4H4O6.4H2O (100 mL). After two distinct layers formed, the reaction

mixture was diluted with EtOAc (100 mL), and the organic and aqueous layers were

separated. The aqueous layer was extracted further with portions of EtOAc (2 × 50 mL),

then, the combined organic layers were dried (MgSO4), and concentrated under reduced

pressure to give a pink oil. The crude oil was subjected to flash column chromatography

on silica gel (30:80 EtOAc/hexane) to give benzylic alcohol 195 (1.97 g, 93% yield,

Rf = 0.38 in 50:50 EtOAc/hexane). (195): 1H NMR (600.13 MHz, CDCl3): δ = 6.88

(app d, 1H, ArH-6), 6.81-6.77 (m, 2H, 2 × ArH), 4.65 (s, 2H, CH2OH), 3.81 (s, 3H,

OCH3), 3.76 (s, 3H, OCH3), 2.50 (s, 1H, CH2OH); 13


153.7 (ArC-5), 151.6 (ArC-2), 130.2 (ArC-1), 114.9 (ArCH-6), 113.1 (ArCH), 111.2

204

(ArCH), 62.0 (CH2OH), 55.9 (2 × OCH3); HRMS (EI): calc. for C9H12O3 [M]+

168.0786, found 168.0786; IR (neat): ν = 3411 (broad, OH), 2943, 2835, 1592, 1498,

1463 cm-1

.

(±)6-(Hydroxymethyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-one (176):

A mixture of ground, flame-dried 4Å molecular sieves (2.85 g), Ti(O-iPr)4 (4.71 mL,

4.48 g, 15.5 mmol) and CH2Cl2 (30 mL) was stirred at room temperature for 1 hour

before being cooled between -30°C and -20°C in a carefully maintained acetone/dry ice

bath, under an atmosphere of argon gas. To this cooled mixture was added L-DIT (4.35

g, 18.6 mmol), and the resulting mixture was stirred between the same temperature

range (-30°C to -20°C) for 20 minutes before the addition of allylic alcohol 172 (2.85 g,

15.5 mmol). After stirring for a further 20 minutes t-BHP (5.60 mL, 5.5 M, 31.0 mmol)

was added in one portion and the mixture was left to stir from -30°C to room

temperature for 18 hours. Workup C: The reaction mixture was then diluted with Et2O

(35 mL), quenched with 19% w/w aq Na2SO4 (15.5 mL), and stirred at room

temperature for an additional 3 hours. The reaction mixture was then vacuum filtered

through celite. The celite was then heated in boiling EtOAc for 10 minutes and re-

filtered. The filtrate was then filtered through a plug of silica gel and concentrated under

reduced pressure to give an oil. The crude oil was subjected to flash column

chromatography (20:80 → 40:60 EtOAc/hexane). The first compound to elute was L-

DIT, as a colourless oil (Rf = in 50:50 EtOAc/hexane), followed by epoxide 176 as

another oil (1.52 g, 49% yield, Rf = 0.46 in 50:50 EtOAc/hexane), and finally by para-

benzoquinone ketal 172 (969 mg, 34% yield, Rf = 0.33 in 50:50 EtOAc/hexane). L-DIT

and epoxide 176 eluted in 20:80 EtOAc/hexane and benzoquinone ketal 172 eluted in

40:60 EtOAc/hexane. The spectroscopic data for para-benzoquinone ketal 172 matched

that reported previously. (176): 1H NMR (600.13 MHz, CDCl3): δ = 6.60 (d, J = 10.8

Hz, 1H, CH=CH-4), 6.10 (dd, J = 2.1 and 10.8 Hz, 1H, CH=CH-3), 4.06 (d, J = 12.9

Hz, 1H, CH2OH), 3.97 (d, J = 12.9 Hz, 1H, CH2OH), 3.48 (d, J = 2.0 Hz, 1H, epoxide

oxymethine), 3.40 (s, 3H, OCH3), 3.29 (s, 3H, OCH3), 2.45 (s, 1H, CH2OH); 13

C NMR

(150.9 MHz, CDCl3): δ = 193.2 (C=O), 142.2 (CH=CH-4), 129.4 (CH=CH-3), 97.5 (C-

205

5), 63.4 (C-6), 58.3 (CH2OH), 53.7 (CH-1), 52.3 (OCH3), 51.0 (OCH3); HRMS (EI):

calc. for C9H13O5 [M + H]+ 201.0763, found 201.0774; IR (neat): ν = 3502 (OH), 2946,

2839, 1693, 1459, 1381, 1287, 1208, 1117, 1070 cm-1

. The ee was determined to be

72%: High pressure liquid chromatography (HPLC) was performed on a Hewlett-

Packard 1050 system using a 250 x 4.6 mm i.d., 5 μm, Chiralcel OD-H normal-phase

column (Daicel Chemical Industries). Mobile phase was 3% isopropanol/hexane with

flow rate of 1mL/min monitoring at 240nm.

Workup A:

A freshly prepared solution of FeSO4.7H2O (15.5 mmol) and tartaric acid (7 mmol) in

D.I. H2O (100 mL) was cooled to 0°C, in an ice water bath. The epoxidation reaction

mixture was allowed to warm to 0°C and then slowly poured into a beaker containing

the pre-cooled stirring FeSO4.7H2O solution. The two-phase mixture was stirred for 5-

10 min and then transferred to a separatory funnel. The two phases were separated and

the aqueous phase was extracted with portions of Et2O (2 × 50 mL). The combined

organic layers were then treated with a pre-cooled (0°C) solution of 30% w/w aq NaOH

in brine and the resulting mixture was stirred vigorously for 1 h at 0°C. Following

transfer to a separatory funnel and dilution with water (50 mL), the two phases were

separated and the aqueous phase was extracted with portions of Et2O (2 × 50 mL). The

combined organic layers were dried over Na2SO4, filtered, and concentrated to give a

crude mixture containing the epoxide.290

Workup B:

A freshly prepared solution of FeSO4.7H2O (15.5 mmol) and tartaric acid (7 mmol) in

D.I. H2O (100 mL) was cooled to 0°C, in an ice water bath. The epoxidation reaction

mixture was allowed to warm to 0°C and then slowly poured into a beaker containing

the pre-cooled stirring FeSO4.7H2O solution. The two-phase mixture was stirred for 5-

10 min and then transferred to a separatory funnel. The two phases were separated and

the aqueous phase was extracted with portions of Et2O (2 × 50 mL). The combined

organic layers were dried over Na2SO4, filtered, and concentrated to give a crude

mixture containing the epoxide.290

206

5-Hydroxy-2-methoxybenzaldehyde (184):

NaBH4 (238 mg, 6.28 mmol) was added, portion-wise, to a mixture of para-

benzoquinone ketal 172 (771 mg, 4.19 mmol) and MeOH (5.00 mL), stirring at 0°C,

under an atmosphere of argon gas. The resulting mixture was stirred for 1 hour at 0°C

before being quenched with 37% w/w aq NH4Cl (4.00 mL) and diluted with EtOAc

(8.00 mL). The organic and aqueous layers were separated and the aqueous layer was

extracted further with portions of EtOAc (2 × 15 mL). The combined organic layers

were dried (MgSO4), filtered, and concentrated under reduced pressure to give

benzaldehyde 184 as a yellow solid (446 mg, 70% yield, Rf = 0.61 in 50:50

EtOAc/hexane). The spectroscopic data for compound 184 matched that reported

previously.287

tert-Butyl(3-(tert-butyldimethylsilyloxy)benzyloxy)dimethylsilane (210); 3-(tert-

butyldimethylsilyloxy)methyl phenol (211); (3-(tert-butyldimethylsilyloxy)phenyl)

methanol (212):

A mixture of alcohol 175 (446 mg, 3.59 mmol), CH2Cl2 (5.00 mL), NEt3 (750 µL, 545

mg, 5.38 mmol), DMAP (56 mg, 0.46 mmol), and TBDMSCl (583 mg, 3.87 mmol)

were stirred at 0°C for 3 hours. After this time, the reaction mixture was diluted with

brine (5.00 mL) and the aqueous and organic layers were separated. The aqueous layer

was extracted further with portions of CH2Cl2 (2 × 20.0 mL), and then the combined

organic layers were dried (MgSO4), filtered, and concentrated under reduced pressure to

give a crude oil. The crude oil was purified via flash column chromatography on silica

207

gel (2:98 → 20:80 EtOAc/hexane). First to elute was di-silyl ether 210 as a colourless

oil (219 mg, 17% yield, Rf = 0.58 in 30:70 EtOAc/hexane). Second to elute was phenol

212 as a colourless oil (332 mg, 39% yield, Rf = 0.44 in 30:70 EtOAc/hexane). Last to

elute was benzyl alcohol 211 (67 mg, 8% yield, Rf = 0.35 in 30:70 EtOAc/hexane) as a

colourless oil. (210): 1H NMR (600.13 MHz, CDCl3): δ = 7.22-7.19 (m, 1H, ArH),

6.93-6.92 (m, 1H, ArH), 6.89 (s, 1H, ArH), 6.76-6.74 (m, 1H, ArH), 4.73 (s, 2H,

CH2OTBDMS), 1.03 (s, 9H, C(CH3)3), 0.99 (s, 9H, C(CH3)3), 0.24 (s, 6H, Si(CH3)2),

0.14 (s, 9H, C(CH3)3); 13

C NMR (150.9 MHz, CDCl3): δ = 155.9 (ArC), 143.2

(ArC),129.2 (ArCH), 119.0 (ArCH), 118.7 (ArCH), 117.8 (ArCH), 64.8

(CH2OTBDMS), 26.1 (C(CH3)3), 25.9 (C(CH3)3), 18.5 (C(CH3)3), 18.4 (C(CH3)3), -4.2

(Si(CH3)2), -5.1 (Si(CH3)2); HRMS (EI): calc. C19H37O2Si2 [M + H]+ 353.2332, found

353.2327; IR (neat): ν = 2956, 2930, 2886, 2858, 1605, 1589, 1472, 1486, 1472, 1463,

1442, 1279, 1256 cm-1

. (212): 1H NMR (600.13 MHz, CDCl3): δ = 7.20-7.18 (m, 1H,

ArH), 6.91-6.87 (m, 2H, 2 × ArH), 6.74-6.73 (m, 1H, ArH), 4.73 (s, 2H,

CH2OTBDMS), 0.99 (s, 9H, C(CH3)3), 0.16 (Si(CH3)2); 13

C NMR (150.9 MHz,

CDCl3): δ = 155.8 (ArC), 142.9 (ArC), 129.6 (ArCH), 118.5 (ArCH), 114.3 (ArCH),

113.4 (ArCH), 65.1 (CH2OTBDMS), 26.1 (C(CH3)3), 18.6 (C(CH3)3), -5.1 (Si(CH3)2);

HRMS (EI): calc. C13H22O2Si [M]+ 238.1389, found 238.1394; IR (neat): ν = 3349

(OH), 2954, 2929, 2884, 2857, 2740, 2712, 1601, 1592, 1487, 1470, 1461, 1257 cm-1

.

(211): 1H NMR (600.13 MHz, CDCl3): δ = 7.22-7.20 (m, 1H, ArH), 6.95-6.93 (m, 1H,

ArH), 6.86-6.85 (m, 1H, ArH), 6.77-6.76 (m, 1H, ArH), 4.63 (s, 2H, CH2OH), 1.80 (s,

2H, CH2OH), 0.99 (s, 9H, C(CH3)3), 0.20 (s, 6H, Si(CH3)2); 13

C NMR (150.9 MHz,

CDCl3): δ = 156.0 (ArC), 142.7 (ArC), 129.7 (ArCH), 119.9 (ArCH), 119.4 (ArCH),

118.7 (ArCH), 65.3 (CH2OH), 25.8 (C(CH3)3), 18.3 (C(CH3)3), -4.3 (Si(CH3)2); HRMS

(EI): calc. C13H22O2Si [M]+ 238.1389, found 238.1385; IR (neat): ν = 3306 (OH), 2954,

2931, 2884, 2858, 2742, 1600, 1592, 1486, 1462, 1456, 1276, 1259 cm-1

.

3-(tert-Butyldimethylsilyloxy)methyl-4,4-dimethoxycyclohexa-2,5-dienone (209):

A mixture of alcohol 172 (348 mg 1.89 mmol), CH2Cl2 (5.00 mL), NEt3 (600 µL, 436

mg, 4.30 mmol), DMAP (33 mg, 0.27 mmol), and TBDMSCl (520 mg, 3.45) were

208

stirred at 0°C for 3 hours. After this time, the reaction mixture was diluted with brine

(5.00 mL) and the aqueous and organic layers were separated. The aqueous layer was

extracted further with portions of CH2Cl2 (2 × 20.0 mL), and then the combined organic

layers were dried (MgSO4), filtered, and concentrated under reduced pressure to give a

crude oil. The crude oil was subjected to flash column chromatography on silica gel

(5:95 EtOAc/hexane) to give TBDMS ether 209 as a yellow oil (445 mg, 79% yield).

(209): 1H NMR (600.13 MHz, CDCl3): δ = 6.72 (d, J = 10.3 Hz, 1H, CH=CH-5), 6.53-

6.52 (m, 1H, C=CH-2), 6.38 (dd, J = 2.2 and 10.3 Hz, 1H, CH=CH-6), 4.38 (d, J = 2.2

Hz, CH2OTBDMS), 3.22 (s, 6H, 2 ×OCH3), 0.90 (s, 9H, C(CH3)3), 0.07 (s, 6H,

Si(CH3)2); 13

C NMR (150.9 MHz, CDCl3): δ = 185.2 (C), 158.4 (C), 143.2 (=CH),

132.6 (=CH), 126.2 (=CH), 95.5 (C), 59.6 (CH2OTBDMS), 51.2 (2 × OCH3), 26.0

(C(CH3)3), 18.4 (C(CH3)3), -5.4 (Si(CH3)2); HRMS (APCI): calc. C15H27O4Si [M + H]+

299.1689, found 299.1679; IR (neat): ν = 2933, 2895, 2857, 2832, 1679 (C=O), 1647,

1621, 1463, 1450, 1406, 1289, 1257 cm-1

.

3-(tert-Butyldimethylsilyloxy)methyl-4-methoxyphenol (213):

NaBH4 (58 mg, 1.53 mmol) was added to a mixture of para-benzoquinone ketal 209

(256 mg, 0.86 mmol), CeCl3.7H2O (429, 1.15 mmol), and MeOH (5 mL), stirring at

room temperature, under an atmosphere of argon gas. The resulting mixture was stirred

at the same temperature for 5 minutes before being quenched with 37% w/w aq NH4Cl

(3 mL) and diluted with EtOAc (10 mL). The entire mixture was then filtered through a

plug of silica (eluted with EtOAc) and concentrated under reduced pressure to give

phenol 213 (208 mg, 90% yield, Rf = 0.50 in 20:80 EtOAc/hexane). (213): 1H NMR

(600.13 MHz, CDCl3): δ = 7.00-6.99 (m, 1H, ArH), 6.69-6.65 (m, 2H, 2 × ArH), 5.19

(s, 1H, OH), 4.73 (s, 2H, CH2OTBDMS), 3.76 (s, 3H, OCH3), 0.96 (s, 9H, C(CH3)3),

0.12 (s, 6H, Si(CH3)2); 13

C NMR (150.9 MHz, CDCl3): δ = 150.2 (ArC), 149.7 (ArC),

131.3 (ArC), 114.4 (ArCH), 113.4 (ArCH), 111.0 (ArCH), 60.2 (CH2OTBDMS), 55.9

(OCH3), 26.2 (C(CH3)3), 18.6 (C(CH3)3), -5.2 (Si(CH3)2); HRMS (EI): calc. C14H24O3Si

[M]+ 268.1495, found 268.1503; IR (neat): ν = 3367 (OH), 2954, 2930, 2886, 2857,

1717, 1599, 1504, 1463, 1439, 1215 cm-1

.

209

3-(tert-Butyldimethylsilyloxy)methyl-4-methoxyphenol (213); 3-(hydroxymethyl)-4-

methoxycyclohex-2-en-1-one (214):

para-Benzoquinone ketal 201 (259 mg, 0.87 mmol) was added to a mixture of

powdered LiAlH4 (40 mg, 1.00 mmol) and THF (10 mL) stirring at 0°C under an

atmosphere of argon gas. The resulting mixture was stirred at 0°C for 1 hour before

being quenched with 63% w/w aq KNaC4H4O6.4H2O (5 mL). After two distinct layers

formed, the reaction mixture was diluted with EtOAc (10 mL), and the organic and

aqueous layers were separated. The aqueous layer was extracted further with portions of

EtOAc (2 × 10 mL) and then the combined organic layers were dried (MgSO4), and

concentrated under reduced pressure to give an oil. The crude oil was subjected to flash

column chromatography on silica gel (5:95 → 20:80 EtOAc/hexane) to give silyl ether

213 as a as a colourless solid (42 mg, % yield, Rf = 0.50 in 20:80 EtOAc/hexane) and

214 also as a colourless solid (Rf = 0.20 in 20:80 EtOAc/hexane). The spectroscopic

data for phenol 213 matched that reported previously. (214): 1H NMR (600.13 MHz,

CDCl3): δ = 5.41 (s, 1H, OCHAHB), 4.88 (s, 1H, OCHAHB), 4.74-4.73 (m, 1H, =CH),

4.02-3.99 (m, 1H, -CH-OCH3), 3.58 (s, 3H, CH3), 2.64-2.62 (m, 1H, CHAHB), 2.54-2.47

(m, 2H, CH2), 2.28-2.24 (m, 1H. CHAHB), 1.90 (s, 1H, OH); 13

C NMR (150.9 MHz,

CDCl3): δ = 152.1 (C), 136.5 (C), 110.9 (CH2), 95.3 (CH), 66.6 (CH), 54.5 (CH3), 40.4

(CH2), 33.6 (CH2); HRMS (FAB): calc. for C8H12O3Na [M + Na]+ 179.0684, found

179.0684; IR (neat): ν = 3270 (OH), 2904, 2835, 1824, 1645, 1604 (C=O), 1469, 1446,

1432, 1355, 1294, 1262 cm-1

.

210

3-(tert-Butyldimethylsilyloxy)methyl-4,4-dimethoxy-1-(1-methyl-1H-imidazol-2-

yl)cyclohexa-2,5-dienol (238):

n-BuLi (809 µL, 1.6 M, 1.30 mmol) was added to a mixture of 1-methylimidazole (110

µL, 113 mg, 1.38 mmol) and THF (5 mL), stirring at -78°C, under an atmosphere of

argon gas. The resulting mixture was stirred at -78°C for 30 minutes before the addition

of para-benzoquinone ketal 201 (322 mg, 1.08 mmol), in one portion. Stirring at -78°C

was then continued for 40 minutes before the reaction mixture was quenched with 37%

w/w aq NH4Cl (3 mL) and diluted with EtOAc (15 mL). The aqueous and organic

layers were separated and the aqueous layer was extracted further with more portions of

EtOAc (3 × 15 mL). The organic layer was then dried (MgSO4), filtered, and

concentrated under reduced pressure to give imidazole 238 as a brown solid (404 mg,

98% yield, Rf = 0.27 in 50:50 EtOAc/hexane). (238): 1H NMR (600.13 MHz, CDCl3): δ

= 6.90 (s, 1H, CH=CHN), 6.80 (s, 1H, CH=CHN), 6.19-6.16 (m, 2H, 2 × C=CH), 6.04

(d, J = 10.2 Hz, 1H, C=CH), 4.41 (dd, J = 1.2 and 15.6 Hz, CH2OTBDMS), 4.24 (dd, J

= 1.2 and 15.6 Hz, CH2OTBDMS), 3.54 (s, 3H, CH3), 3.32 (s, 3H, CH3), 3.15 (s, 3H,

CH3), 0.87 (s, 9H, 3 × CH3), 0.05 (s, 3H, SiCH3), 0.03 (s, 3H, SiCH3); 13

C NMR (150.9

MHz, CDCl3): δ = 147.6 (C), 139.1 (C), 136.1 (CH), 127.5 (CH), 126.2 (CH), 126.0

(CH), 123.8 (CH), 95.3 (C), 66.3 (C), 59.6 (CH2), 51.4 (CH3), 50.3 (CH3), 33.8 (CH3),

26.0 (CH3), 18.5 (C), -5.2 (CH3), -5.4 (CH3); HRMS (APCI): calc. for C19H33N2O4Si

[M + H]+ 381.2210, found 381.2211; IR (neat): ν = 3354, 2929, 2856, 1674, 1638,

1470, 1394, 1361, 1326, 1282, 1249, 1205, 1147, 1123 cm-1

.

2-Iodoxybenzoic acid, IBX (241):

A mixture of 2-iodobenzoic acid 378 (19.0 g, 76.6 mmol), Oxone (71.2 g, 232 mmol),

and D.I. H2O (180 mL) was stirred at 73°C for 3 hours. After this time, the reaction

211

mixture was left to stand at room temperature for 18 hours and then cooled in an ice

bath for 1.5 hours. The copious amount of white precipitate that formed was then

collected by vacuum filtration, washed with H2O (6 × 30 mL) and acetone (2 × 30 mL),

and dried overnight in a dessicator to give IBX 241 (18.7 g, 87% yield) as a white solid.


literature.317

Dess-Martin periodinane (379):

A stirring mixture of IBX 241 (10.3 g, 41.5 mmol), glacial AcOH (17.0 mL) and Ac2O

(34 mL) were heated to 90°C, under an atmosphere of argon, and kept at this

temperature until all the solids dissolved (~30 minutes). After this time, heating and

stirring were discontinued and the reaction mixture was slowly allowed to cool to and

remain at room temperature for 18 hours, a white solid precipitated during this time.

The resulting solid was isolated by vacuum filtration under argon, and washed with

portions of Et2O (3 × 20 mL) to give Dess-martin periodinane 379 as a colourless solid

(12.6 g, 72% yield). The spectroscopic data for compound 379 matched that reported


2,2-Dimethoxy-5-oxo-7-oxabicyclo[4.1.0]hept-3-ene-1-carbaldehyde (177):

A stirred mixture of alcohol 176 (776 mg, 3.88 mmol), IBX (3.26 g, 11.6 mmol), and

EtOAc (10 mL) was stirred at reflux for 18 hours. After this time, the reaction mixture

was cooled to room temperature, filtered through a plug of silica gel (eluted with

EtOAc), and concentrated under reduced pressure to give aldehyde 177 as an oil

(668 mg, 87% yield, Rf = 0.73 in 50:50 EtOAc/hexane). The product was used without

further purification. (177): 1H NMR (600.13 MHz, CDCl3): δ = 10.17 (s, 1H, CHO),

212

6.65 (d, J = 11.0 Hz, CH=CH-3), 6.08 (dd, J = 1.7 and 11.0 Hz, CH=CH-4), 3.49 (d, J =

1.7 Hz, 1H, CH-6), 3.46 (s, 3H, OCH3), 3.43 (s, 3H, OCH3); 13

C NMR (150.9 MHz,

CDCl3): δ = 193.3 (CHO), 190.3 (C=O), 142.4 (CH=CH), 127.6 (CH=CH), 97.1 (C),

62.2 (C), 56.9 (CH-6), 51.8 (OCH3), 50.8 (OCH3); HRMS (EI): calc. for C9H11O5 [M +

H]+ 199.0606, found 199.0615; IR (neat): ν = 2946, 2839, 1719, 1699, 1459, 1389,

1281, 1187, 113, 1059 cm-1

.

para-Acetamidobenzenesulfonyl azide (256):

A solution of NaN3 (5.40 g, 83.1 mmol) in H2O (50.0 mL) was added to a mixture of

sulfonyl chloride (15.0 g, 64.2 mmol) and acetone (130 mL). The resulting mixture was

left to stir at room temperature for 18 hours. After this time, the reaction mixture was

poured into a beaker containing H2O (384 mL) and stirred at room temperature for 2

hours. The product that precipitated out was isolated by vacuum filtration and washed

with H2O (2 × 25 mL). The crude product was dried in a vacuum desiccator over NaOH

for 24 hours, and then recrystallised from toluene to give azide 256 as a white solid

(11.8 g, 77% yield). The spectroscopic data for compound 256 matched that reported

previously in the literature.322,383

Diethyl 1-diazo-2-oxopropylphosphonate (258):

NaH (55% paraffin, 240 mg, 5.50 mmol) was added in portions to a mixture of the

phosphonate 257 (1.04 g, 5.4 mmol) and toluene, stirring at 0°C, under an atmosphere

of argon. After the evolution of gas had ceased, a solution of azide 256 (1.30 g, 5.40

mmol) in THF (2.00 mL) was added drop-wise and the resulting mixture was left to stir

at room temperature for 18 hours. After this time, the mixture was diluted with hexane,

213

filtered through a pad of celite (eluted with Et2O), and concentrated under reduced

pressure to give a crude yellow oil. The crude oil was subjected to flash column

chromatography on silica gel (20:80 EtOAc/hexane) to give the Bestmann-Ohira

reagent 258 as a yellow oil (854 mg, 73% yield, Rf = 0.30 in 20:80 EtOAc/hexane). The


literature.384

(5Z)-1-ethynyl-2,2,6-trimethoxy-5-(methoxymethylidene)cyclohex-3-en-1-ol (254):

A solution of aldehyde 177 (240 mg, 1.32 mmol) in MeOH (4.00 mL) was added to a

mixture of K2CO3 (360 mg, 2.60 mmol), MeOH (12.0 mL), and the Bestmann-Ohira

reagent 243 (336 mg, 1.53 mmol) that had been stirring for 40 minutes, at room

temperature, under an atmosphere of argon gas. The resulting mixture was stirred for 3

hours, also at room temperature. After this time, the solvents were removed in vacuo

and the residue was dissolved in Et2O (5.00 mL) and H2O (5.00 mL). The aqueous and

organic layers were separated, the organic layer was washed with brine (5.00 mL), dried

(Na2SO4), and concentrated under reduced pressure to give a crude oil. The crude oil

was subjected to flash column chromatography on silica gel (5:95 → 10:90

EtOAc/hexane) to give alkyne 254 as a yellow solid (127 mg, 36% yield, Rf = 0.25 in

20:80 EtOAc/hexane). (254): 1H NMR (600.13 MHz, CDCl3): δ = 6.11 (d, J = 10.2 Hz,

1H, CH=CH), 5.91 (s, 1H, C=CH(OCH3), 5.77 (d, J = 10.2 Hz, 1H, CH=CH), 4.75 (s,

1H, OH), 3.47 (s, 3H, OCH3), 3.32 (s, 4H, OCH3, H-6), 3.26 (s, 3H, OCH3), 3.25 (s, 3H,

OCH3), 2.46 (s, 1H, CH); 13

C NMR (150.9 MHz, CDCl3): δ = 133.0 (C=C), 131.2

(C), 129.0 (C=C), 125.5 (C=C), 101.7 (CH), 98.2 (C), 81.6 (C), 73.0 (CH), 72.5 (C),

52.8 (C), 52.7 (CH3), 50.9 (CH3), 50.1 (CH3); HRMS (EI): calc. for C14H20O5Na [M +

Na]+ 291.1208, found 291.1202; IR (neat): ν = 3444 (OH), 3282 (C C-H), 2944 (=C-

H), 2834 (=C-H), 2249, 2112 (C C), 1774, 1689 (C=C) cm-1

.

214

(Iodomethyl)triphenylphosphonium iodide (260):

CH2I2 (19.8 g, 74.0 mmol) was added to a stirred suspension of PPh3 (14.9 g, 57.0

mmol) and toluene (20 mL), under an atmosphere of argon gas. The resulting mixture

was stirred at 50°C for 18 hours. After this time, the reaction mixture was cooled in an

ice bath and the solid precipitate was collected on a sintered glass frit. The filtered solid

was washed with toluene (3 × 20 mL) and Et2O (2 × 20 mL), then dried under vacuum

to give the phosphonium salt 260 (15.3 g, 51% yield) as a white solid. The

spectroscopic data for 260 matched that reported previously in the literature.385

1-(2,2-Dibromoethenyl)-5-(dibromomethylidene)-7-oxabicyclo[4.1.0]hept-3-en-2-

one (272): 6-(2,2-dibromoethenyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-

one (178):

A mixture of tetrabromomethane (696 mg, 2.1 mmol) and CH2Cl2 (10 mL) was cooled

to 0°C. A mixture of triphenylphosphine (1.05 g, 4.0 mmol) and CH2Cl2 (10 mL), also

at 0°C, was then transferred to the previous mixture via cannula. The resulting mixture

was stirred at 0°C for 15 minutes. After this time, the aldehyde 177 (218 mg, 1.1 mmol)

in CH2Cl2 (10 mL) was added drop-wise, the cooling bath was removed, and the

mixture was left to stir at room temperature for 18 hours. The reaction mixture was then

diluted with hexane (30 mL), copious amounts of triphenylphosphine oxide precipitated

out of solution. The reaction mixture was filtered through a sintered glass frit and the

solid was washed with a 50:50 Et2O/hexane mixture (2 × 30 mL). The filtrate was then

concentrated under reduced pressure to give a crude mixture of triphenylphosphine

oxide and the desired product. A mixture of Et2O/hexane (10 mL) was added to the

crude product and the solvent was decanted and then filtered through a silica plug eluted

with 50:50 Et2O/hexane to give an oil. The crude oil was subjected to flash column

215

chromatography on silica gel (2:98 EtOAc/hexane) to give tetrabromo alkene 272 (153

mg, 30% yield, Rf = 0.79 in 20:80 EtOAc/hexane) and dibromoalkene 178 (58 mg, 15%

yield, Rf = 0.58 in 20:80 EtOAc/hexane) as pale yellow oils. (272): 1H NMR (600.13

MHz, CDCl3): δ = 7.21 (dd, J = 2.4 and 10.2 Hz, 1H, CH=CH-4), 6.82 (s, 1H,

CH=CBr2), 6.05 (d, J = 10.2 Hz, 1H, CH=CH-3), 4.67 (d, J = 2.4 Hz, 1H, H-6); 13

C

NMR (150.9 MHz, CDCl3): δ = 190.2 (C=O), 137.6, 133.0, 130.1, 125.3, 106.9, 97.7,

61.6 (CH); HRMS (APCI): calc. for C9H5O2Br4 [M + H]+ 460.7023, found 460.7050;

IR (neat): ν = 3040, 1673, 1589, 1538, 1400, 1278, 1164, 1089, 931, 910, 867, 774,

728, 672, cm-1

. (178): 1H NMR (600.13 MHz, CDCl3): δ = 6.96 (s, 1H, CH=CBr2),

6.61 (d, J = 11.4 Hz, 1H, CH=CH), 6.06 (dd, J = 1.8 and 11.4 Hz, CH=CH), 3.39 (d,

J = 1.8 Hz, 1H, H-5), 3.49 (s, 3H, CH3), 3.36 (s, 3H, CH3); 13

C NMR (150.9 MHz,

CDCl3): δ = 192.o (C=O), 142.9 (C=CH), 129.4 (C=CH), 127.8 (C=CH), 97.0 (C), 95.6

(C), 63.7 (C), 57.9 (CH), 52.0 (OCH3), 51.0 (OCH3); HRMS (APCI): calc. for

C10H10O4Br2 [M]+ 353.8926, found 353.8925; IR (neat): ν = 3044, 2943, 2837, 1694

(C=O), 1625, 1462, 1380, 1286, 1245, 1209, 1189, 1133, 1120, 1074 cm-1

.

1-(2,2-dibromoethenyl)-5-(dibromomethylidene)-2,2-dimethoxy-7-oxabicyclo[4.1.0]

hept-3-ene (273); 6-(2,2-dibromoethenyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-

en-2-one (178):

A mixture of tetrabromomethane (766 mg, 2.3 mmol) and CH2Cl2 (11 mL) was cooled

to 0°C. A mixture of triphenylphosphine (1.16 g, 4.4 mmol) and CH2Cl2 (11 mL), also

at 0°C, was then transferred to the previous mixture via cannula. The resulting mixture

was stirred at 0°C for 15 minutes. After this time, NEt3 (122 mg, 1.2 mmol) was added,

followed by the aldehyde 177 (240 mg, 1.2 mmol) in CH2Cl2 (11 mL). The cooling bath

was removed, and the mixture was left to stir at room temperature for 18 hours. The

reaction mixture was then diluted with hexane (30 mL), copious amounts of

triphenylphosphine oxide precipitated out of solution. The reaction mixture was filtered

through a sintered glass frit and the solid was washed with a 50:50 Et2O/hexane mixture

(2 × 30 mL). The filtrate was then concentrated under reduced pressure to give a crude

216

mixture of triphenylphosphine oxide and the desired product. Et2O/hexane (10 mL) was

added to the crude mixture and the solvent was decanted and then filtered through a

silica plug eluted with 50:50 Et2O/hexane to give an oil. The crude oil was subjected to

flash column chromatography on silica gel (2:98 EtOAc/hexane) to give tetrabromo

alkene 273 (141 mg, 23% yield, Rf = 0.79 in 20:80 EtOAc/hexane) and dibromoalkene

178 (255 mg, 60% yield, Rf = 0.58 in 20:80 EtOAc/hexane) as pale yellow oils. (273):

1H NMR (600.13 MHz, CDCl3): δ = 6.96 (s, 1H, CH=CBr2), 6.61 (d, J = 10.9 Hz, 1H,

CH=CH-4), 6.07 (dd, J = 2.1 and 10.9 Hz, 1H, CH=CH-3), 3.59 (d, J = 2.1 Hz, 1H, H-

6), 3.49 (s, 3H, 3H, OCH3), 3.37 (s, 3H, 3H, OCH3); 13


= 192.1 (C=O), 142.9 (CH=CBr2), 129.4 (CH=CH-4), 127.9 (CH=CH-3), 97.0

(C=CBr2), 95.4 (C-5), 63.7 (C-6), 58.0 (CH-1), 52.1 (OCH3), 51.0 (OCH3); HRMS

(APCI): calc. for C11H11O3Br4 [M + H]+ 510.7401, found 510.7405; IR (neat): ν = 2939,

2833, 1733, 1679, 1625, 1558, 1461, 1391, 1282, 1209, 1191, 1132, 1116, 1086 cm-1

.

6-(Bromoethynyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-one (275):

A mixture of dibromoalkene 178 (349 mg, 0.99 mmol) and THF (10.0 mL) was cooled

to -100°C in a flame dried flask, under an atmosphere of argon gas. To this cooled

mixture was added NaHMDS (1 M, 1.50 mL, 1.50 mmol), in one portion. The resulting

mixture was stirred at -100°C for 1 hour. After this time, the reaction mixture was

quenched with 37% w/w aq NH4Cl (5 mL), diluted with Et2O (10 mL), and warmed to

room temperature. The organic and aqueous layers were separated, and the aqueous

layer was extracted further with portions of Et2O (2 × 10 mL). The combined organic

layers were dried (Na2SO4), filtered, and concentrated under reduced pressure to give a

crude solid. The crude solid was subjected to flash column chromatography on silica gel

(5:95 EtOAc/hexane) to give a colourless solid. This colourless solid was recrystallised

form hexane to give bromo alkyne 275 as colourless needles (120 mg, 45% yield,

Rf = 0.53 in 20:80 EtOAc/hexane). (275): m.p. 82°C; 1H NMR (600.13 MHz, CDCl3):

δ = 6.53 (d, J = 10.9 Hz, 1H, CH=CH-4), 6.00 (dd, J = 2.0 and 10.9 Hz, 1H, CH=CH-

3), 3.64 (s, 3H, OCH3), 3.59 (d, J = 2.0 Hz, 1H, H-1), 3.41 (s, 3H, OCH3); 13

C NMR

(150.9 MHz, CDCl3): δ = 191.0 (C=O), 143.2 (CH=CH-4), 126.6 (CH=CH-3), 95.5

217

(C(OCH3)2), 74.0 (C), 59.0 (CH-1), 55.6 (C), 51.8 (OCH3), 50.8 (C), 48.0 (OCH3);

HRMS (EI): calc. for C10H9O4Br [M]+ 271.9684, found 271.9680; IR (neat): ν = 3050,

2990, 2937, 2832, 2212, 1688 (C=O), 1458, 1396, 1322, 1285, 1188, 1130, 1078, 1049

cm-1

.

6-Ethynyl-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-one (179):

A mixture of dibromo alkene 178 (1 mmol) and THF (10.0 mL) was cooled to -100°C

in a flame dried flask, under an atmosphere of argon gas. To this cooled mixture was

added NaHMDS (1.50 mmol), in one portion. The resulting mixture was stirred at -

100°C for 20 minutes. After this time, a mixture of t-Buli (1.50 mmol) was cooled to -

100°C and also transferred to this mixture, drop-wise via cannula. The resulting solution

was stirred for 10 minutes at -100°C before being diluted with Et2O and quenched with

37% w/w aq NH4Cl. The aqueous and organic layers were then separated and the

aqueous layer was extracted further with portions of Et2O (× 2). Filtration of the organic

layers through a plug of silica and concentration of the solvent gave a crude oil. The

crude oil was subjected to column chromatography (5:95 EtOAc/hexane) to give alkyne

179 as a colourless oil. (179): 1H NMR (600.13 MHz, CDCl3): δ =6.55 (d, J = 10.8 Hz,

H-4), 6.02 (dd, J = 2.4 and 10.8 Hz, H-3), 3.66 (s, 3H, OCH3), 3.60 (d, J = 2.4 Hz, H-1),

3.42 (s, 3H, OCH3), 2.56 (s, 1H, -C CH); 13

C NMR (150.9 MHz, CDCl3): δ = 191.1

(C), 143.2 (C=CH), 126.7 (C=CH), 95.5 (C), 77.5 (C), 74.8 (C), 59.1 (C CH), 54.7

(C), 51.8 (CH3), 50.8 (CH3); HRMS (EI): calc. for C10H10O4 [M]+ 194.0579, found

194.0582; IR (neat): ν = 3272 (C C-H), 2947, 2840, 2127 (C C-H), 1695 (C=O),

1462, 1389, 1281, 1210, 1189, 1135, 1077 cm-1

.

218

(±)-6-(2,2-Dibromoethenyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-ol (285

and 286):

DIBAL-H (1.7 M, 1.00 mL, 1.70 mmol) was added, in one portion, to a pre-cooled

(-78°C) mixture of ketone 178 (301 mg, 0.85 mmol) stirring in THF (8.00 mL), under

an atmosphere of argon gas. The resulting mixture was warmed to 0°C and stirred for 2

hours. After this time, the reaction mixture was quenched with 63% w/w aq

KNaC4H4O6.4H2O (4 mL) and left to stir until two clear and distinct layers formed (~

1.5 hours). The mixture was then diluted with EtOAc (10.0 mL) and the aqueous and

organic layers were separated. The aqueous phase was then extracted further with

portions of EtOAc (2 × 10.0 mL). The combined organic layers were then washed with

brine (2 × 4.00 mL), filtered through a plug of silica, and concentrated under reduced

pressure to give a crude oil, which solidified upon standing. The crude mixture was

used without further purification to give alcohols 285 and 286 as a diastereomeric mix

(266 mg, 88% yield, Rf = 0.62 in 50:50 EtOAc/hexane, 285:286, 10:1). (285 and 286):

1H NMR ( MHz, CDCl3): δ = 6.95 (s, 1H, CH=CBr2), 6.92 (s, 0.1H, CH=CBr2), 6.04-

6.02 (m, 0.1H, H-3), 5.99 (ddd, J = 2.4, 5.4, and 10.8 Hz, 1H, H-3), 5.78 (d, J = 10.8

Hz, 1H, H-4), 5.68-5.65 (m, 0.1H, H-4), 4.54-4.52 (m, 0.1H, H-2), 4.43-4.39 (m, 1H, H-

2), 3.77-3.76 (m, 0.1H, H-1), 3.61-3.59 (m, 1H, H-1), 3.48 (s, 0.1H, OH), 3.44 (s, 1H,

OH), 3.41 (s, 0.3H, CH3), 3.40 (s, 3H, CH3), 3.34 (s, 3H, CH3), 3.28 (s, 0.3H, CH3); 13

C

NMR (150.9 MHz, CDCl3): δ = (285): 131.7 (C=CH), 129.9 (C=CH), 126.8 (C=CH),

97.4 (C), 93.8 (C), 63.1 (CH), 61.8 (C), 59.4 (CH), 51.7 (OCH3), 50.7 (OCH3); (286):

131.5 (C=CH), 130.6 (C=CH), 127.0 (C=CH), 97.7 (C), 94.2 (C), 64.7 (CH), 63.2 (C),

59.7 (CH), 51.6 (OCH3), 51.0 (OCH3); HRMS (EI): calc. for C10H12O4Br2 [M]+

353.9102, found 353.9113; IR (neat): ν = 3429 (OH), 3037, 2941, 2835, 2364, 1687,

1632, 1620, 1463, 1393, 1318, 1230, 1091, 980, 954, 936, 797 cm-1

.

219

tert-Butyl[6-(2,2-dibromovinyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-

yloxy]dimethylsilane (289):

A mixture of alcohol 285 (173 mg, 0.49 mmol), DMF (2.00 mL), and imidazole (188

mg, 2.76 mol) were stirred at room temperature for 30 minutes under an atmosphere of

argon gas. After this time, the reaction mixture was cooled to 0°C and TBDMSCl (265

mg, 1.77 mmol) was added in one portion. The resulting mixture was left to stir for 2

hours at 0°C before the mixture was diluted with H2O (2 mL) and Et2O (5.00 mL). The

aqueous and organic layers were separated and the aqueous layer was extracted further

with portions of Et2O (2 × 5.00 mL). The combined organic layers were dried (Na2SO4)

and concentrated under reduced pressure to give a crude oil. The crude oil was dried

under vacuum (~0.01 mm Hg) to remove any traces of DMF before it was subjected to

flash column chromatography on silica gel (2:98 EtOAc/hexane) to give TBDMS ether

289 (119 mg, 52% yield, Rf = in 20:80 EtOAc/hexane). (289): 1H NMR (500.13 MHz,

CDCl3): δ = 6.98 (s, 1H. CH=CBr2), 5.84, ddd, J = 2.5, 5.0, and 11.0 Hz, 1H, CH=CH-

3), 5.65 (dd, J = 0.5 and 11.0 Hz, 1H, CH=CH-4), 4.45-4.42 (m, 1H, CH-2), 3.57-3.56,

m, 1H, CH-1), 3.40 (s, 3H, OCH3), 3.33 (s, 3H, OCH3), 0.88 (s, 9H, C(CH3)3), 0.13 (s,

3H, SiCH3), 0.11 (s, 3H, SiCH3); 13

C NMR (125.8 MHz, CDCl3): δ = 132.1

(CH=CBr2), 130.0 (CH=CH-3), 123.5 (CH=CH-4), 97.6 (C(OMe)2), 93.3 (CH=CBr2),

63.5 (COTBDMS), 61.8 (C-6), 60.6 (C-1), 51.9 (OCH3), 50.7 (OCH3), 25.8 (C(CH3)3),

18.1 (C(CH3)3), -4.4 (SiCH3), -4.6 (SiCH3); HRMS (EI): calc. C16H27O4SiBr2 [M + H]+

469.0045, found 469.0049; IR (neat): ν = 2954, 2857, 1621, 1463, 1395, 1253, 1079

cm-1

.

(6-(Bromoethynyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-yloxy)(tert-butyl)

dimethylsilane (295):

220

A mixture of dibromoalkene 294 (142 mg, 0.31 mmol) and THF (5.00 mL) was cooled


mixture was added NaHMDS (1 M, 620 µL, 0.62 mmol), in one portion. The resulting

mixture was stirred at -100°C for 30 minutes. After this time, the reaction mixture was

quenched with 37% w/w aq NH4Cl (2.50 mL), diluted with Et2O (5.00 mL), and

warmed to room temperature. The organic and aqueous layers were separated, and the

aqueous layer was extracted further with portions of Et2O (2 × 5.00 mL). The combined

organic layers were dried (Na2SO4), filtered, and concentrated under reduced pressure to

give a crude oil. The crude oil was used without further purification to give bromo

alkynes 295 as an oil (95.0 mg, 79% yield, Rf = 0.46 in 10:90 EtOAc/hexane). (295): 1H

NMR (600.13 MHz, CDCl3): δ = 5.77 (ddd, J = 1.8, 4.8, and 10.7 Hz, 1H, CH-3), 5.56

(dd, J = 0.8 and 10.7 Hz, 1H, CH-4), 4.40-4.39 (m, 1H, CH-2), 3.53 (s, 3H, OCH3),

3.44-3.43 (m, 1H, CH-1), 3.33 (s, 3H, OCH3), 0.89 (s, 9H, C(CH3)3), 0.13 (s, 3H,

SiCH3), 0.11 (s, 3H, SiCH3); 13

C NMR (150.9 MHz, CDCl3): δ = 129.0 (CH=CH-3),

124.0 (CH=CH-4), 96.0 (C-5), 76.3 (C CBr), 63.0 (CH-2), 62.4 (CH-1), 53.8 (C-6),

51.1 (OCH3), 51.0 (OCH3), 45.9 (C CBr), 25.8 (C(CH3)3), 78.1 (C(CH3)3), -4.45

(SiCH3), -4.59 (SiCH3); HRMS (APCI): calc. C16H26BrO4Si [M + H]+ 389.0784, found

389.0781; IR (neat): ν = 2954, 2896, 2858, 2213, 1463, 1390, 1140 1059 cm-1

.

4-(5-(tert-Butyldimethylsilyloxy)-2,2-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-1-yl)-

2-methylbut-3-yn-2-ol (296):

A mixture of bromo-alkyne 295 (115 mg, 0.30 mmol) and THF (5 mL) was cooled to

-100°C in a flame dried flask, under an atmosphere of argon gas. To this cooled mixture

was added t-BuLi (0.30 mmol), in one portion. The resulting mixture was stirred at

-100°C for 40 minutes. After this time, acetone was added to the reaction mixture and it

was left to stir at -100°C for a further 25 minutes. The reaction mixture was then

removed from the cold bath and quenched with 37% w/w aq NH4Cl (5 mL), diluted

with Et2O (10 mL), and warmed to room temperature. The organic and aqueous layers

were separated, and the aqueous layer was extracted further with portions of Et2O (2 ×

10 mL). The combined organic layers were dried (Na2SO4), filtered, and concentrated

221

under reduced pressure to give a crude oil. The crude oil was subjected to flash column

chromatography on silica gel (20:80 EtOAc/hexane) to give tertiary alcohol 296 as an

oil (Rf = 0.26 in 30:70 EtOAc/hexane). (296): 1H NMR (600.13 MHz, CDCl3): δ = 5.76

(ddd, J = 2.4, 4.8, and 10.8 Hz, 1H, CH=CH-6), 5.54 (dd, J = 1.2 and 10.8 Hz, 1H,

CH=CH-1), 4.40 (dt, J = 1.2 and 4.8 Hz, 1H, H-5), 3.56 (s, 3H, OCH3), 3.40 (dd, J = 1.2

and 2.4 Hz, 1H, H-4), 3.33 (s, 3H, OCH3)1.53 (2 × s, 6H, C(CH3)2OH), 0.89 (s, 9H,

C(CH3)3), 0.13 (s, 3H, SiCH3), 0.12 (s, 3H, SiCH3).

3-Ethynylphenol (299):

A mixture of diisopropyl amine (1 mL, 717 mg, 7.09 mmol), THF (1 mL), and n-BuLi

(4.7 mL, 1.5 M) were stirred at 0°C, under an atmosphere of argon gas, for 40 minutes.

After this time, the reaction mixture was cooled to -78°C, a solution of

(trimethylsilyl)diazomethane 259 solution was added (1.8 mL, 2 M, 3.55 mmol), and

the mixture was left to stir at the same temperature for 3 hours. After 3 hours, aldehyde

181 (300 mg, 2.46 mmol) was added in one portion and the mixture was left to stir at

-78°C for 1 hour, and then at room temperature for 16 hours. After this time, the

reaction mixture was quenched with ice water (5 mL) and acidified to pH 2 with 1 M aq

HCl. The reaction mixture was diluted with Et2O (10 mL) and the aqueous and organic

layers were separated. The aqueous layer was extracted further with Et2O (2 × 10 mL),

then the combined organic layers were dried (MgSO4), filtered, and concentrated under

reduced pressure to give a crude oil. The crude oil was subjected to flash column

chromatography on silica gel (5:95 EtOAc/hexane) to give alkyne 299 as a pale yellow

oil (194 mg, 67% yield, Rf = 0.59 in 30:70 EtOAc/hexane). The spectroscopic data for

compound 299 matched that reported previously in the literature.386

222

3-Bromo-4,4-dimethoxycyclohexa-2,5-dien-1-one (301):



chromatography (5:95 EtOAc/hexane) to give para-benzoquinone ketal 301 (543 mg,

31% yield, Rf = 0.38 in 20:80 EtOAc/hexane) as a yellow oil. The spectroscopic data for

compound 301 matched that reported previously in the literature.387,388

3-Bromo-4-methoxyphenol (304):

A mixture of acetate 303 (520 mg, 2.1 mmol), LiOH (56 mg, 2.2 mmol), MeOH (8 mL),

and H2O (1 mL) was stirred at room temperature for 30 minutes. After this time, the

reaction mixture was concentrated under reduced pressure to remove the MeOH, diluted

with H2O (10 mL), and adjusted to a pH of 2 with 1 M aq HCl. The reaction mixture

was then diluted with CH2Cl2 (20 mL) and the organic and aqueous phases were

separated. The aqueous phase was extracted further with CH2Cl2 (2 × 20 mL) and the

combined organic layers were dried (MgSO4), filtered and concentrated under reduced

pressure to give phenol 304 (420 mg, 98% yield, Rf = 0.39 in 30:70 EtOAc/hexane) as a

colourless solid. The product was used without further purification. The spectroscopic

data for compound 304 matched that reported previously in the literature.389

3-Bromo-4,4-dimethoxycyclohexa-2,5-dien-1-one (301):

223



chromatography on silica gel (5:95 EtOAc/hexane) to give para-benzoquinone ketal

301 (345 mg, 71% yield, Rf = 0.38 in 20:80 EtOAc/hexane) as a yellow oil. The


literature.387,388

4-Methoxy-3-(3-methylbut-3-en-1-yn-1-yl)phenol (306); 4,4-dimethoxy-3-(3-methyl

but-3-en-1-yn-1-yl)cyclohexa-2,5-dien-1-one (173):

A mixture of para-benzoquinone ketal 301 (100 mg, 0.43 mmol), PdCl2(PPh3)2 (76 mg,

0.11 mmol), DMF (1.7 mL), alkyne 305 (160 µL, 1.72 mmol) CuI (41 mg, 0.22 mmol),

and NEt3 (240 µL, 1.72 mmol) was stirred, under an atmosphere of argon gas, for 3

hours at 60°C, then 12 hours at room temperature. After this time, the reaction mixture

was diluted with Et2O (100 mL) and washed with 1 M aq HCl (2 × 75 mL) and brine (1

× 100 mL). The organic layer was then dried (MgSO4), filtered, and concentrated under

reduced pressure to give a crude mixture. The crude mixture was subjected to flash

column chromatography on silica gel (20:80 EtOAc/hexane) to give para-benzoquinone

ketal 173 (4 mg, 4% yield, Rf = 0.61 in 30:70 EtOAc/hexane) and phenol 306 (29 mg,

36% yield, Rf = 0.59 30:70 EtOAc/hexane). (306): 1H NMR (600.13 MHz, CDCl3): δ =

6.91 (app d, 1H, ArH), 6.71-6.75 (m, 1H, ArH), 6.71 (app d, 1H, ArH), 6.19 (s, 1H,

OH), 5.38 (s, 1H, C=CH), 5.27 (s, 1H, C=CH), 3.80 (s, 1H, OCH3), 1.96 (s, 1H,

C=CH3); 13

C NMR (150.9 MHz, CDCl3): δ = 154.1 (C), 149.2 (C), 126.8 (C), 122.3

(CH2), 120.0 (ArCH), 116.7 (ArCH), 113.2 (C), 112.6 (ArCH), 95.0 (C C), 84.4 (C

C), 56.6 (OCH3), 23.4 (CH3); HRMS (EI): calc. for C12H12O2 [M]+ 188.0837, found

188.0835; IR (neat): ν = 3391 (OH), 2952, 2836, 2203, 1704, 1610, 1582, 1497, 1455.

1430, 1373, 1307, 1277 cm-1

. (173): 1H NMR (600.13 MHz, CDCl3): δ = 6.71 (d, J =

10.8 Hz, 1H, CH=CH-5), 6.50 (d, J = 2.4 Hz, 1H, CH=CH-2), 6.39 (d, J = 2.4 and 10.8

Hz, 1H, CH=CH-6), 5.50-5.49 (m, 1H, CCH3=CH), 5.42-5.41 (m, 1H, CCH3=CH), 3.36

(s, 6H, 2 × OCH3), 1.97 (s, 3H, CCH3=CH2); 13

C NMR (150.9 MHz, CDCl3): δ = 184.5

(C=O), 144.0 (CH=CH-5), 140.2 (C-3), 134.4 (CH=CH-2), 131.4 (CH=CH-6), 126.2

224

(C), 125.1 (CCH3=CH2), 102.8 (C), 94.3 (C-4), 83.9 (C), 51.4 (2 × OCH3), 22.9

(CCH3=CH2); HRMS (EI): calc. C13H14O3 [M]+ 218.0943, found 218.0941; IR (neat): ν

= 3649, 2944, 2834, 2193, 1674, 1631, 1610, 1588, 1458 cm-1

.

3-(3-Hydroxy-3-methylbut-1-yn-1-yl)-4-methoxyphenyl acetate (308):

A mixture of bromobenzene 303 (3.31 g, 13.5 mmol), PdCl2(PPh3)2 (474 mg,

0.68 mmol), CH3CN (13.5 mL), alkyne 307 (3.95 mL, 3.40 g, 40.4 mmol), CuI

(467 mg, 2.45 mmol), and NEt3 (5.65 mL, 4.09 g, 40.5 mmol) was de-gassed via the

freeze-pump-thaw method (× 3), and then left to reflux for 16 hours, under an

atmosphere of argon gas. After this time, the reaction mixture was concentrated under

reduced pressure, diluted with EtOAc (10 mL), filtered through a plug of silica gel

(eluted with 50:50 EtOAc/hexane), and then concentrated under reduced pressure to

give a crude residue. The crude mixture was subjected to flash column chromatography

on silica gel (10:90 → 30:70 EtOAc/hexane) and recrystallised from Et2O/hexane to

give alkyne 308 (3.15 g, 94% yield, Rf = 0.23 in 10:90 EtOAc/hexane) as a pale yellow

solid. (308): m.p. 65°C; 1H NMR (600.13 MHz, CDCl3): δ = 7.10 (app d, 1H, ArH-2),

6.98 (app dd, 1H, ArH-6), 6.82 (app d, 1H, ArH-5), 3.84 (s, 3H, OCH3), 2.49 (s, 1H,

(CH3)2OH), 2.25 (s, 3H, C=OCH3), 1.60 (s, 6H, (CH3)2OH); 13

C NMR (150.9 MHz,

CDCl3): δ = 169.7 (C=OCH3), 157.8 (ArC-4), 143.7 (ArC-3), 126.5 (ArCH-2), 122.6

(ArCH-6), 112.9 (ArC-1), 111.4 (ArCH-5), 98.9 (C), 77.6 (C C-C(CH3)2OH), 65.7

(C), 56.3 (OCH3), 31.5 ((CH3)2OH), 21.1 (C=OCH3); HRMS (EI): calc. for C14H16O4

[M]+ 248.1049, found 248.1056; IR (neat): ν = 3429 (OH), 2983, 2048, 1732, 1637,

1495, 1414, 1371 cm-1

.

225

4-Methoxy-3-(3-methylbut-3-en-1-yn-1-yl)phenyl acetate (309); 4-methoxy-3-(3-

methyl but-3-en-1-yn-1-yl)phenol (306):

A mixture of tertiary alcohol 308 (580 mg, 2.34 mmol), TsOH.H2O (22 mg, 0.12

mmol), and toluene (10 mL) were heated at 60°C for 2 hours, under an atmosphere of

argon gas. After this time, the reaction mixture was cooled to room temperature, filtered

through silica gel (eluted with EtOAc), and concentrated under reduced pressure to give

a crude oil. The crude oil was subjected to flash column chromatography on silica gel

(5:95 EtOAc/hexane) to give acetate 309 (108 mg, 20% yield, Rf = 0.69 in 50:50

EtOAc/hexane) and phenol 306 (264 mg, 60% yield Rf = 0.59 50:50 EtOAc/hexane).

The spectroscopic data for phenol 306 matched that reported previously. (309): 1H

NMR (600.13 MHz, CDCl3): δ = 7.12 (app d, 1H, ArH), 6.97-6.95 (m, 1H, ArH), 6.80

(app d, 1H, ArH), 5.39 (s, 1H, C=CH), 5.28 (s, 1H, C=CH), 3.81 (s, 3H, OCH3), 2.22 (s,

3H, CH3), 1.97 (s, 3H, CH3); 13

C NMR (150.9 MHz, CDCl3): δ = 169.5 (C=O), 157.5

(C), 143.5 (C), 126.7 (C), 126.1 (ArCH), 122.5 (ArCH), 122.1 (C=CH2), 113.1 (C),

111.1 (ArCH), 95.2 (C C), 83.8 (C C), 56.0 (OCH3), 23.3 (CH3), 20.8 (CH3); HRMS

(EI): calc. for C14H14O3 [M + H]+ 231.1011, found 231.1016; IR (neat): ν = 2946, 2838,

1760 (C=O), 1612, 1494, 1462, 1441, 1415, 1368, 1312, 1291, 1255, 1265, 1179, 1153,

1121 cm-1

.

4-Methoxy-3-(3-methyl but-3-en-1-yn-1-yl)phenol (306):

A mixture of acetate 309 (264 mg, 1.15 mmol), LiOH (69 mg, 2.88 mmol), MeOH

(4 mL), and H2O (0.5 mL) was stirred at 60°C for 30 minutes. After this time, the

reaction mixture was concentrated under reduced pressure to remove the MeOH, diluted

with H2O (5 mL), and adjusted to a pH of 2 with 1 M aq HCl. The reaction mixture was

226

then diluted with CH2Cl2 (10 mL) and the organic and aqueous phases were separated.

The aqueous phase was extracted further with CH2Cl2 (2 × 10 mL) and the combined

organic layers were dried (MgSO4), filtered, and concentrated under reduced pressure to

give phenol 306 (212 mg, 98% yield, Rf = 0.59 in 50:50 EtOAc/hexane) as a colourless

solid. The product was used without further purification. The spectroscopic data for

phenol 306 matched that reported previously.

4,4-Dimethoxy-3-(3-methylbut-3-en-1-yn-1-yl)cyclohexa-2,5-dien-1-one (173):



chromatography on silica gel (5:95 EtOAc/hexane) to give para-benzoquinone ketal

173 (181 mg, 43% yield, Rf = 0.61 in 30:70 EtOAc/hexane) as a yellow oil. The

spectroscopic data for ketal 173 matched that reported previously.

4,4-Dimethoxy-3-[(2-methyloxiran-2-yl)ethynyl]cyclohexa-2,5-dien-1-one (311):

A mixture of buffer (0.05 M Na2B4O7.10H2O in 4 × 10-4

M aq Na2(EDTA), 11.8 mL),

acetonitrile (11.8 mL), alkene 173 (126 mg, 0.58 mmol), N(Bu)4.HSO4 (12 mg, 0.04

mmol), and ketone 310 (140 mg, 0.54 mmol) was cooled in an ice bath. A solution of

Oxone (667 mg, 2.17 mmol) in 4 × 10-4

M aq Na2(EDTA) (5.1 mL), and a solution of

K2CO3 (630 mg, 4.56 mmol) in water (5.1 mL) were then added drop-wise to the cooled

reaction mixture, uniformly, over 1.5 hours. The reaction was then immediately

quenched with water (10 mL) and hexane (20 mL), and the mixture was extracted with

227

EtOAc (3 × 40 mL). The combined organic layers were dried (Na2SO4), filtered, and

concentrated under reduced pressure to give a crude oil. The crude material was

subjected to column chromatography (5:95 → 20:80 EtOAc/hexane) to give epoxide

311 (141 mg, 96% yield, Rf = 0.33 in 30:70 EtOAc/hexane) as a yellow solid. (311): 1H

NMR (600.13 MHz, CDCl3): δ = 6.69 (d, J = 10.2 Hz, 1H, CH=CH-5), 6.48 (d, J = 2.4

Hz, 1H, CH=CH-2) 6.36 (d, J = 2.4 and 10.2 Hz, 1H, CH=CH-6), 3.32 (s, 3H, OCH3),

3.31 (s, 3H, OCH3), 3.08 (d, J = 5.4 Hz, 1H, C-O-CH), 2.82 (d, J = 5.4 Hz, 1H, C-O-

CH), 1.60 (s, 3H, C-O-CCH3); 13

C NMR (150.9 MHz, CDCl3): δ = 184.3 (C=O), 144.0

(CH=CH), 139.2 (C), 135.5 (CH=CH), 131.4 (CH=CH), 100.6 (C), 94.2 (C), 77.4 (C),

55.8 (C-O-CH2), 51.4 (2 × OCH3), 47.5 (C), 22.5 (C-O-CCH3); HRMS (EI): calc.

C13H15O4 [M + H]+ 235.0965, found 235.0962.

228

229


1-[(4-Methylphenyl)sulfonyl]-1H-pyrrole (332):19

A solution of freshly distilled pyrrole 331 (1.98 g, 29.5 mmol) in THF (8 mL) was

added drop-wise to a stirred suspension of 60% NaH (1.27 g, 31.8 mmol) and THF (8

mL), under an argon gas atmosphere. The resulting mixture was stirred for 30 minutes

at room temperature, after which time, a solution of p-toluenesulfonyl chloride (5.79 g,

30.3 mmol) in THF (8 mL) was also added drop-wise. The resulting mixture was left to

stir at room temperature for a further 3 hours, after which time, it was quenched with

H2O (15 mL) and diluted with EtOAc (15 mL). The organic and aqueous layers were

separated, and then the aqueous layer was extracted further with portions of EtOAc (2 ×

15 mL). The combined organic layers were concentrated under reduced pressure to give

a crude solid. The crude material was subjected to column chromatography

(EtOAc/hexane 5:95) to give pyrrole 332 (6.27 g, 96 % yield, Rf = 0.75 in 20:80

EtOAc/hexane) as a white solid. The spectroscopic data for 332 matched that reported

previously in the literature.390,391

(2E)-1-(1-[(4-Methylphenyl)sulfonyl]-1H-pyrrol-2-yl)but-2-en-1-one (329):

A mixture of pyrrole 332 (4.44 g, 20.1 mmol), carboxylic acid 333 (7.24 g, 84.1 mmol),

and TFAA (11.7 mL, 17.68 g, 84.2 mmol) in CH2Cl2 (100 mL) was stirred at room

temperature under an argon gas atmosphere for 4 hours. The resulting mixture was

diluted with EtOAc (100 mL), washed with 22% w/w aq Na2CO3 (50 mL) and brine (50

mL), then dried (MgSO4), filtered, and concentrated under reduced pressure. Flash

column chromatography (5:95 EtOAc/hexane) of the crude product, on silica gel,

yielded pyrrole 329 (2.79 g, 48% yield, Rf = 0.38 in 20:80 EtOAc/hexane) as an orange

230

solid. The spectroscopic data for compound 329 matched that reported previously in the

literature.352

[3-Methyl-3-(4-methylpent-3-en-1-yl)oxiran-2-yl]methanol (335):

VO(acac)2 (152 mg, 0.58 mmol) was added cautiously, in small portions, to a stirred

solution of geraniol 334 (2 mL, 1.78 g, 11.5 mmol), t-BHP in decane (3.2 mL, 5.5 M,

17.3 mmol), and CH2Cl, (60 mL), at 0°C, under an atmosphere of argon gas. The

resulting mixture was stirred at 0°C for 10 minutes, then at room temperature for 1 hour,

after which time, it was quenched with 23% w/w aq Na2SO3 (20 mL) and stirred for a

further 1 hour or until the solution turned colourless. The mixture was diluted with

CH2Cl2 (50 mL), the organic and aqueous layers were separated, and the aqueous layer

was extracted with portions of EtOAc (2 × 50 mL). The combined organic extracts were

filtered through a plug of silica (eluted with EtOAc) to, and then concentrated under

reduced pressure to give a colourless crude oil. The crude material was subjected to

column chromatography (10:90→30:80 EtOAc/hexane) to give the epoxide 335 as a

colourless oil ( 1.64 g, 83% yield, Rf = 0.31 in 20:80 EtOAc/hexane). The spectroscopic


3-Methyl-3-(4-methylpent-3-en-1-yl)oxirane-2-carbaldehyde (336):

IBX (12.6 g, 45.0 mmol) was added in one portion to a stirred solution of alcohol 335

(2.55 g, 15.0 mmol) and EtOAc (10 mL). The resultant mixture was stirred at reflux for

18 hours, open to the atmosphere. After heating for this period of time, the reaction

mixture was cooled to room temperature, filtered through a plug of silica (eluted with

EtOAc), and concentrated under reduced pressure to give a crude oil. The crude

material was subjected to column chromatography 5:95 EtOAc/hexane) to give

aldehyde 336 as a pure oil (1.88 g, 75% yield, Rf = 0.74 in 20:80 EtOAc/hexane). The

spectroscopic data for 336 matched that reported previously in the literature.392

231

3-[(E)-2-Iodoethenyl]-2-methyl-2-(4-methylpent-3-en-1-yl)oxirane (342):

NaHMDS (1.8 mL, 1 M in THF, 1.8 mmol) was added to a suspension of the Wittig salt

260 (946 mg, 179 mmol) and THF (5 mL), stirring at room temperature, under an

atmosphere of argon gas. The resultant mixture was stirred at room temperature for 15

minutes, before being cooled to 0°C, followed by the drop-wise addition of the aldehyde

336 (200 mg, 1.19 mmol) in THF (5 mL). After the resultant reaction mixture was

stirred at 0°C for 30 minutes, it was quenched with 37% w/w aq NH4Cl (5 mL). The

solid precipitate was filtered off, washed with Et2O, and the filtrate was extracted with

more Et2O (3 × 30 mL). The combined organic extracts were dried (Na2SO4), filtered,

and concentrated under reduced pressure to give a crude oil. The crude oil was

subjected to flash column chromatography (2:98 EtOAc/hexane) to give (Z)-vinyl

iodide 342 as a colourless oil (236 mg, 68% yield Rf = 0.89 in 20:80 EtOAc/hexane).

(342): 1H NMR (399.85 MHz, CDCl3): δ = 6.54 (dd, J = 1.2 and 7.8 Hz, 1H, H-1), 6.23

(dd, J = 6.6 and 7.8 Hz, 1H, H-2), 5.17-5.13 (m, 1H, H-7), 3.42 (dd, J = 1.2 and 7.8 Hz,

1H, H-3), 2.19-2.12 (m, 2H, CH2), 1.81-1.70 (m, 1H, CH), 1.72 (s, 3H, CH3), 1.64 (s,

3H, CH3), 1.62-1.50 (m, 2H, CH), 1.31 (s, 3H, CH3); 13


= 137.5 (=CH), 132.3 (C), 123.5 (=CH), 123.3 (=CH), 67.6 (C), 65.3 (OCH), 38.3

(CH2), 25.8 (CH3), 23.7 (CH2), 17.8 (2 × CH3); HRMS (EI): calc. C11H17IO [M]+

292.032417, found 292.03115.

3-Ethynyl-2-methyl-2-(4-methylpent-3-en-1-yl)oxirane (344):

A mixture of CBr4 (10.8 g, 32.6 mmol) and CH2Cl2 (130 mL) was cooled to -78°C in a

flame dried flask, under an atmosphere of argon gas. To this cooled mixture was added

PPh3 (17.3 g, 66.0 mmol), in one portion. The resulting mixture was stirred at -78°C for

5 minutes, after which time, the mixture was warmed to 0°C and stirred for 15 minutes.

The mixture was then re-cooled to -78°C and a mixture of the aldehyde 336 (2.92 g,

232

17.1 mmol), NEt3 (3.6 mL, 2.61 g, 25.8 mmol), and CH2Cl2, (10 mL) at

-78°C was transferred to the previous mixture via cannula. The mixture was left to stir

from -78°C to room temperature over a 4 hour period. After this time, the reaction

mixture was diluted with hexane (200 mL), copious amounts of triphenylphosphine

oxide precipitated out of solution at this point. The reaction mixture was vacuum

filtered on a sintered glass frit and the solid was washed multiples times with a 50:50

Et2O/hexane mixture (4 × 100 mL). The filtrate was then concentrated under reduced

pressure to give a crude mixture of PPh3=O and the desired product. Hexane (15 mL)

was added to the crude mixture, then the solvent was decanted, and filtered through a

silica plug (eluted with 50:50 Et2O/hexane) to give an oil. The crude oil was subjected

to flash column chromatography on silica gel (2:98 EtOAc/hexane) to give dibromo

alkene 347 A mixture of dibromo alkene 347 (713 mg, 2.27 mmol) and THF (22 mL)

was cooled to -78°C in a flame dried flask, under an atmosphere of argon gas. To this

cooled mixture was added n-BuLi (3.1 mL, 1.6 M, 4.99 mmol), in one portion. The

resulting mixture was stirred at -78°C for 30 minutes. After this time, the reaction

mixture was quenched with 37% w/w aq NH4Cl (10 mL), diluted with Et2O (5 mL), and

warmed to room temperature. The reaction mixture was filtered through silica gel

(eluted with Et2O) and concentrated under reduced pressure to give a crude oil. The

crude oil was subjected to column chromatography (2:98 EtOAc/hexane) to give alkyne

344 as a colourless oil (328 mg, 88% yield, Rf = 0.47 in 5:95 EtOAc/hexane). (344): 1H

NMR (600.13 MHz, CDCl3): δ = 5.06-5.03 (m, 1H, C(CH3)2=CH), 3.19 (d, J = 1.2 Hz,

1H, OCH), 2.35 (d, J = 1.2 Hz, 1H, C C-H), 2.06 (dt, J = 7.8 Hz, 2H, CH2-CH2), 1.66

(d, J = 1.2 Hz, 3H, CH3), 1.65-1.60 (m, 1H, CH2-CH2), 1.59 (s, 3H, CH3), 1.51-1.46 (m,

1H, CH2-CH2), 1.42 (s, 3H, CH3); 13

C NMR (150.9 MHz, CDCl3): δ = 132.5 (C), 123.2

(CH), 79.8 (C), 73.6 (C), 62.7 (C), 50.5 (CH), 37.1 (CH2), 25.7 (CH3), 23.7 (CH2), 18.0

(CH3), 17.7 (CH3); HRMS (EI): calc. C11H16O [M]+ 165.1279, found 165.1286; IR

(neat): ν = 3305, 2969, 2930, 1451, 1384, 1245, cm-1

.

3-(2,2-Dibromoethenyl)-2-methyl-2-(4-methylpent-3-en-1-yl)oxirane (347):

A mixture of CBr4 (10.8 g, 32.6 mmol) and CH2Cl2 (130 mL) was cooled to -78°C in a

flame dried flask, under an atmosphere of argon gas. To this cooled mixture was added

233

PPh3 (17.3 g, 66.0 mmol), in one portion. The resulting mixture was stirred at -78°C for

5 minutes, after which time, the mixture was warmed to 0°C and stirred for 15 minutes.

The mixture was then re-cooled to -78°C and a mixture of the aldehyde 336 (2.92 g,

17.1 mmol), NEt3 (3.6 mL, 2.61 g, 25.8 mmol), and CH2Cl2, (10 mL) at

-78°C was transferred to the previous mixture via cannula. The mixture was left to stir

from -78°C to room temperature over a 4 hour period. After this time, the reaction

mixture was diluted with hexane (200 mL), copious amounts of triphenylphosphine

oxide precipitated out of solution at this point. The reaction mixture was vacuum

filtered on a sintered glass frit and the solid was washed multiples times with a 50:50

Et2O/hexane mixture (4 × 100 mL). The filtrate was then concentrated under reduced

pressure to give a crude mixture of PPh3=O and the desired product. Hexane (15 mL)

was added to the crude mixture, then the solvent was decanted, and filtered through a

silica plug (eluted with 50:50 Et2O/hexane) to give an oil. The crude oil was subjected

to flash column chromatography on silica gel (2:98 EtOAc/hexane) to give dibromo

alkene 347 (4.88 g, 87% yield, Rf = 0.47 in 5:95 EtOAc/hexane) as a colourless oil.

(347): 1H NMR (600.13 MHz, CDCl3): δ = 6.31 (d, J = 7.0 Hz, 1H, CH=CBr2), 5.10-

5.07 (m 1H, C(CH3)2=CH-3), 3.38 (d, J = 7.0 Hz, 1H, C(CH3)-O-CH), 2.12-2.08 (m,

2H, CH2-CH2), 1.73-1.70 (m, 1H, CH2-CH2), 1.68 (d, J = 1.0 Hz, 3H, CH3), 1.60 (s, 3H,

CH3), 1.52-1.47 (m, 1H, CH2-CH2), 1.30 (s, 3H, CH3); 13

C NMR (150.9 MHz, CDCl3):

δ = 134.6 (CH), 132.5 (C), 123.3 (CH), 93.1 (C), 62.9 (C), 62.4 (CH), 38.3 (CH2), 25.8

(CH3), 23.8 (CH2), 17.8 (2 × CH3); HRMS (APCI): calc. C11H17OBr2 [M +H]+

322.9646, found 322.9642; IR (neat): ν = 2967, 2928, 1615, 1450, 1384, 1245, 1119,

1072, 825, 766, 702, cm-1

.

3-[(E)-2-Bromoethenyl]-2-methyl-2-(4-methylpent-3-en-1-yl)oxirane (348):

n-BuLi (5.4 mL, 1.6 M, 8.67 mmol) was added to a mixture of dibromo alkene 347

(2.81 g, 8.67 mmol) and THF (85 mL), stirring at -100°C, under an argon gas

atmosphere. The resulting mixture was stirred at -100°C for 5 minutes before being

quenched with MeOH (5 mL) and 37% w/w aq NH4Cl (15 mL). The reaction mixture

was then warmed to room temperature and diluted with Et2O (10 mL). The aqueous and

organic layers were separated, the aqueous layer was extracted further with Et2O (3 × 50

234

mL), the combined organic layers were filtered through a plug of silica to dry (eluted

with Et2O), and then the mixture was concentrated under reduced pressure to give a

crude oil. The crude oil was dissolved in EtOH (15 mL) and then added to a mixture of

CuI (1.65 g, 8.67 mmol) and conc. aq NH3 (5 mL). The resulting mixture was stirred for

20 minutes at room temperature. After this time, the reaction mixture was diluted with

CHCl3 (70 mL) and the aqueous and organic layers were separated. The aqueous layer

was extracted further with CH2Cl2 (3 × 70 mL), the combined organic extracts were

filtered through a plug of silica to dry (eluted with Et2O), and then the mixture was

concentrated under reduced pressure to give a crude solid. The crude solid was

subjected to flash column chromatography (2:98 EtOAc/hexane) to give bromo alkene

348 as a colourless oil (1.21 g, 57% yield, Rf = 0.63 in 5:95 EtOAc/hexane). (348): 1H

NMR (600.13 MHz, CDCl3): δ = 6.41 (dd, J = 0.6 and 13.8 Hz, 1H, CH=CHBr), 6.12

(dd, J = 7.2 Hz, 13.8 Hz, 1H, CH=CHBr), 5.08-5.05 (m, 1H, C(CH3)2=CH), 3.18 (d, J =

7.2 Hz, 1H, CCH3-O-CH), 2.11-2.04 (m, 2H, CH2-CH2), 1.70-1.66 (m, 4H, CH2-CH2,

CH3), 1.60 (s, 3H, CH3), 1.51-1.46 (m, 1H, CH2-CH2), 1.26 (s, 3H, CH3); 13

C NMR

(150.9 MHz, CDCl3): δ = 133.4 (CH=CHBr), 132.4 (C), 123.4 (C(CH3)2=CH), 110.3

(CH=CHBr), 62.7 (C), 62.4 (OCH3), 38.3 (CH2), 25.8 (CH3), 23.8 (CH2), 17.8 (CH3),

16.7 (CH3); HRMS (EI): calc. C11H17BrO [M]+ 244.0464, found 244.0461; IR (neat): ν

= 2973, 1715, 1616, 1455, 1378, 1082, 937, 828, 652, 528 cm-1

.

[3-Methyl-3-(4-methylpent-3-en-1-yl)oxiran-2-yl]methyl acetate (351):

A mixture of alcohol 334 (2.04 g, 12.0 mmol), CH2Cl2 (8 mL), acetic anhydride

(1.36 mL, 14.4 mmol), triethylamine (2.4 mL, 17.1 mmol), and DMAP (29 mg, 0.24

mmol) was stirred at room temperature, under an atmosphere of argon gas, for 30

minutes. After this time, the reaction mixture was diluted with CH2Cl2 (20 mL) and

washed with 2N HCl (2 ×15 mL), 9% w/w aq NaHCO3 (3 ×15 mL), and brine (1 ×15

mL). The organic layer was then filtered through a plug of silica (eluted with Et2O), to

dry, and concentrated under reduced pressure to give an oil. The crude material was

subjected to column chromatography (5:95 EtOAc/hexane) to give the acetate 351 as a

colourless oil (2.49 g, 98% yield, Rf = 0.63 in 20:80 EtOAc/hexane). The spectroscopic


235

(±)-2,3-Dihydroxy-3,7-dimethyloct-6-en-1-yl acetate (352):

A mixture of epoxide 351 (12.1 g, 57.0 mmol), THF (60 mL), H2O (30 mL), and 70%

HClO4 (1 mL) was stirred at 100°C for 15 minutes. After this time, the reaction mixture

was cooled to room temperature and extracted with EtOAc (3 × 70 mL). The organic

layer was filtered through a plug of silica (eluted with EtOAc), to dry, and concentrated

under reduced pressure to give a colourless oil. The crude oil was subjected to flash

column chromatography on silica gel (10:90 → 20:80 EtOAc/hexane) to give diol 352

(6.39 g, 49% yield, Rf = 0.42 in 50:50 EtOAc/hexane) as a colourless oil. (352): 1H

NMR (600.13 MHz, CDCl3): δ = 5.12-5.09 (m, 1H, C(CH3)2=CH), 4.31 (dd, J = 2.6

and 11.6 Hz, 1H, OCHAHB), 4.06 (dd, J = 8.5 and 11.6 Hz, 1H, OCHAHB), 3.67 (d, J =

8.5 Hz, 1H, CHOH), 2.23 (s, 1H, OH), 2.14-2.05 (m, 2H, CH2-CH2), 2.09 (s, 3H, CH3),

1.82 (s, 1H, OH), 1.68 (s, 3H, CH3), 1.67-1.62 (m, 1H, CH2-CH2), 1.62 (s, 3H, CH3),

1.41-1.36 (m 1H, CH2-CH2), 1.22 (s, 3H, CH3); 13


171.6 (C=O), 132.4 (C), 124.2 (CH), 75.8 (CH), 73.7 (C), 66.0 (CH2), 37.2 (CH2), 25.8

(CH3), 23.4 (CH3), 22.1 (CH2), 21.1 (CH3), 17.8 (CH3); HRMS (APCI): calc. for

C12H23O4 [M + H]+ 231.1596, found 231.1587; IR (neat): ν = 3460, 2971, 2926, 1726

(C=O), 1452, 1374, 1243, 1076, 1038, 979, 928, 837, 787, 734 cm-1

.

(±)-[2,2,5-Trimethyl-5-(4-methylpent-3-en-1-yl)-1,3-dioxolan-4-yl]methyl acetate

(353):

A mixture of diol 352 (2.4 g, 10.4 mmol), 2,2-dimethoxypropane (9 mL, 24.5 mmol),

acetone (1 mL, 13.6 mmol), and p-toluenesulfonic acid (99 mg, 0.52 mmol) was stirred

at room temperature, under an atmosphere of argon gas, for 30 minutes. After this time,

the reaction mixture was filtered through a plug of silica gel, eluted with Et2O, and

concentrated under reduced pressure to give a colourless oil that was used without

236

further purification (2.70 g, 96% yield, Rf = 0.57 in 10:90 EtOAc/hexane). (353): 1H

NMR (600.13 MHz, CDCl3): δ = 5.09-5.06 (m, 1H, =CH), 3.90 (dd, J = 3.6 and 7.8 Hz,

1H, -OCH), 3.79-3.75 (m, 1H, -OCH), 3.65-3.62(m, 1H, -OCH), 2.16-2.13 (m, 1H,

-CHACHB), 2.01-1.95 (m, 1H, -CHACHB), 1.66 (s, 3H, CH3), 1.57 (s, 3H, CH3), 1.57-

1.50, 2H, CH2), 1.42 (s, 3H, CH3), 1.36 (s, 3H, CH3), 1.27 (s, 3H, CH3), 1.07 (s, 3H,

CH3); 13

C NMR (150.9 MHz, CDCl3): δ = 170.8 (C=O), 131.9 (C), 124.1 (CH), 108.2

(C), 81.9 (CH), 81.4 (C), 63.6 (OCH2), 35.0 (CH2), 28.3 (CH3), 27.0 (CH3), 25.7 (CH3),

23.1 (CH3), 21.8 (CH3), 20.9 (CH3), 17.6 (CH3); HRMS (APCI): calc. for C15H26O4Na

[M + Na]+ 293.1723, found 293.1730; IR (neat): ν = 2983, 2934, 1742 (C=O), 1456,

1371, 1040, 1001 cm-1

.

(±)-[2,2,5-Trimethyl-5-(4-methylpent-3-en-1-yl)-1,3-dioxolan-4-yl]methanol (354):

K2CO3 (4.6 g, 33.2 mmol) was dissolved in water (10 mL) and added to a mixture of

acetate 353 (3 g, 11.1 mmol) and MeOH (20 mL), The resultant mixture was stirred at

100°C for 3 hours. After this time, the reaction mixture was cooled to room temperature

and diluted with EtOAc (100 mL) and 37% w/w aq NH4Cl (15 mL). The aqueous and

organic layers were separated and the aqueous layer was extracted further with portions

of EtOAc (2 × 60 mL). The organic layer was dried (MgSO4) and concentrated under

reduced pressure to give an oil. The crude oil was subjected to flash column

chromatography on silica gel (10:90 EtOAc/hexane) to give alcohol 354 (2.3 g, 91%

yield, Rf = 0.73 in 50:50 EtOAc/hexane) as a colourless oil. (354): 1H NMR (600.13

MHz, CDCl3): δ = 5.10-5.07 (m, 1H, C(CH3)2=CH), 3.91 (dd, J = 3.0 and 7.8 Hz, 1H,

O-CH), 3.80-3.76 (m, 1H, CH2OH), 3.67-3.62 (m, 1H, CH2OH), 2.20-2.12 (m, 1H,

C=CH-CH2), 2.03-1.98 (m, 1H, C=CH-CH2), 1.75 (s, 1H, OH), 1.67 (s, 3H, CH3), 1.60

(s, 3H, CH3), 1.54 (dt, J = 4.8 and 13.2 Hz, 1H, CH2-CH2), 1.43 (s, 3H, CH3), 1.38 (s,

3H, CH3), 1.28 (s, 3H, CH3), 1.16 (dt, J = 4.8 and 13.2 Hz, 1H, CH2-CH2); 13

C NMR

(150.9 MHz, CDCl3): δ = 131.8 (C), 124.4 (CH), 107.9 (C), 85.1 (CH), 81.4 (C), 61.3

(CH2OH), 35.4 (CH2), 28.5 (CH3), 27.1 (CH3), 25.8 (CH3), 23.4 (CH3), 22.0 (CH2), 17.7

(CH3); HRMS (APCI): calc. for C13H24O3Na [M + Na]+ 251.1618, found 251.1633; IR

(neat): ν = 3467 (OH), 2984, 2933, 2874, 1651, 1456, 13378, 1342, 1219 cm-1

.

237

(±)2,2,5-Trimethyl-5-(4-methylpent-3-en-1-yl)-1,3-dioxolane-4-carbaldehyde (355):

A mixture of alcohol 354 (3.5 g, 15.3 mmol), IBX (11.6 g, 41.4 mmol), and EtOAc

(10 mL) were heated at reflux for 4 hours. After this time, the reaction mixture was

cooled to room temperature, filtered through a plug of silica gel (eluted with EtOAc)

and concentrated under reduced pressure to give an oil. The crude product was


aldehyde 355 (2.84 g, 82% yield, Rf = 0.68 in 20:80 EtOAc/hexane) as a colourless oil.

(355): 1H NMR (600.13 MHz, CDCl3): δ = 9.74 (d, J = 2.4 Hz, 1H, CHO), 5.06-5.04

(m, 1H, C(CH3)2=CH), 4.10 (d, J = 2.4 Hz, 1H, O-CH), 2.14-2.06 (m, 1H, CH2-CH2),

2.06-1.99 (m, 1H, CH2-CH2), 1.66 (s, 3H, CH3), 1.58 (s, 3H, CH3), 1.56-1.53 (m, 1H,

CH2-CH2), 1.54 (s, 3H, CH3), 1.42 (s, 3H, CH3), 1.41 (s, 3H, CH3), 1.35-1.30 (m, 1H,

CH2-CH2); 13

C NMR (150.9 MHz, CDCl3): δ = 200.5 (CHO), 132.2 (C), 123.8 (CH),

110.1 (C), 88.1 (CH), 84.0 (C), 36.7 (CH2), 28.2 (CH3), 27.2 (CH3), 25.8 (CH3), 24.7

(CH3), 22.2 (CH2), 17.2 (CH3); HRMS (APCI): calc. for C13H23O3 [M + H]+ 227.1647,

found 227.1624; IR (neat): ν = 2984, 2935, 1736 (C=O), 1457, 1378, 1219, 1091, 1071,

872, 819 cm-1

.

(±)-5-(2,2-Dibromoethenyl)-2,2,4-trimethyl-4-(4-methylpent-3-en-1-yl)-1,3-

dioxolane (356):

A mixture of tetrabromomethane (2.82 g, 8.50 mmol) and CH2Cl2 (34 mL) were cooled


mixture was added triphenylphosphine (4.75 g, 18.1 mmol) in one portion. After the

addition of triphenylphosphine and subsequent stirring for 5 minutes at -78°C, the

mixture was warmed to 0°C and stirred for 15 minutes. After this time, the mixture was

re-cooled to -78°C and the aldehyde 355 (1.20 g, 5.30 mmol), dissolved in CH2Cl2,

238

(6 mL) was added. The mixture was left to stir from -78°C to room temperature over a 4

hour period. After this time, the reaction mixture was diluted with hexane (120 mL),

copious amounts of triphenylphosphine oxide precipitated out of solution. The reaction

mixture was filtered on a sintered glass frit and the solid was washed multiples times

with a 50:50 Et2O/hexane mixture (4 × 100 mL). The filtrate was then concentrated

under reduced pressure to give a crude mixture of triphenylphosphine oxide and the

desired product. Hexane (10 mL) was added to the crude mixture and the solvent was

decanted and then filtered through a silica plug eluted with 50:50 Et2O/hexane to give

an oil. The crude oil was subjected to flash column chromatography on silica gel

(1.5:98.5 EtOAc/hexane) to give the dibromo alkene 356 (1.51 g, 75% yield, Rf = 0.63

in 5:95 EtOAc/hexane) as a very pale yellow oil. (356): 1H NMR (600.13 MHz,

CDCl3): δ = 6.49 (dd, J = 8.4 Hz, 1H, CH=CBr2), 5.11-5.08 (m, 1H, C(CH3)2=CH), 4.60

(dd, J = 8.4 Hz, 1H, O-CH), 2.15-2.08 (m, 1H, CH2-CH2), 2.03-1.97 (m, 1H, CH2-CH2),

1.67 (s, 3H, CH3), 1.60 (s, 3H, CH3), 1.55 (dt, J = 4.8 and 12.6 Hz, 1H, CH2-CH2), 1.42

(s, 3H, CH3), 1.38 (s, 3H, CH3), 1.33 (s, 3H, CH3), 1.28 (dt, J = 4.8 and 12.6 Hz, 1H,

CH2-CH2); 13

C NMR (150.9 MHz, CDCl3): δ = 134.2 (CH), 131.8 (C), 124.2 (CH),

108.6 (C), 93.3 (C), 84.3 (CH), 83.5 (C), 36.4 (CH2), 28.4 (CH3), 27.2 (CH3), 25.8

(CH3), 23.6 (CH3), 22.1 (CH2), 17.7; HRMS (EI): calc. for C14H22Br2O2 [M]+ 379.9986,

found 378.9908; IR (neat): ν = 2983, 2932, 1615, 1455, 1377, 1218, 1199, 1088, 1050,

990, 919, 877, 821, 761 cm-1

.

1-[(4-Methylphenyl)sulfonyl]-1H-pyrrole-2-carbaldehyde (361):

Aldehyde 361 (7.2 g, 75.7 mmol) in THF (20 mL) was added drop-wise to a stirred

suspension of 60% NaH (3.6 g, 90.0 mmol) and THF (70 mL), under an argon gas

atmosphere. The resulting mixture was stirred for 30 minutes at room temperature, after

which time, a solution of p-toluenesulfonyl chloride (20 g, 105 mmol) in THF (30 mL)

was also added drop-wise. The resulting mixture was left to stir at room temperature for

a further 18 hours, after which time, it was quenched with H2O (300 mL) and diluted

with EtOAc (80 mL). The organic and aqueous layers were separated, and then the

aqueous layer was extracted further with portions of EtOAc (2 × 40 mL). The combined

239

organic layers were concentrated under reduced pressure to give a crude solid. The

crude material was subjected to column chromatography (5:95 EtOAc/hexane) to give

aldehyde 361 as a purple solid (16.4 g, 87% yield, Rf = 0.36 in 20:80 EtOAc/hexane).

The spectroscopic data for 361 matched that reported previously in the literature.372

1-[1-[(4-Methylphenyl)sulfonyl]-1H-pyrrol-2-yl]but-2-yn-1-ol (363):

Grignard reagent 362 (42 mL, 0.5 M, 20.8 mmol) was added drop wise to a mixture of

aldehyde 361 (4.33 g, 17.4 mmol) and THF (15 mL) stirring at 0°C, in a flame-dried

flask, under an atmosphere of argon gas. The resulting mixture was stirred at 0°C to

room temperature for 1 hour before being quenched with 37% w/w aq NH4Cl (15 mL)

and diluted with EtOAc (50 mL). The aqueous and organic layers were separated, then

the aqueous layer was extracted further with portions of EtOAc (2 × 50 mL). The

combined organic extracts were dried (MgSO4), filtered and concentrated under reduced

pressure to give propargyl alcohol 363 as brown oil (4.73 g, 94% yield, Rf = 0.33 in

20:80 EtOAc/hexane). The oil was used without further purification. (363): 1H NMR

(600.13 MHz, CDCl3): δ = 7.70 (d, J = 8.4 Hz, 2H, 2 × ArH), 7.26 (d, J = 8.4 Hz, 2H, 2

× ArH), 7.24 (dd, J = 1.8 and 3.0 Hz, 1H, C=CH), 6.22 (t, J = 3.6 Hz, 1H, C=CH), 5.72

(d, J = 1.8 Hz, 1H, C=CH), 3.47 (s, 1H, C-CH), 3.27 (s, 1H, OH), 2.37 (s, 3H, CH3),

1.82 (d, J = 2.4 Hz, 3H, CH3); 13

C NMR (150.9 MHz, CDCl3): δ = 145.3 (C), 136.0

(C), 135.3 (CH), 130.0 (CH), 126.9 (CH), 124.2 (CH), 115.2 (CH), 111.6 (C), 82.1 (C),

77.0 (CH), 57.2 (CH3), 3.6 (CH3); HRMS (APCI): calc. for C15H16NO3S [M + H]+

290.0851, found 290.0842; IR (neat): ν = 2923, 1732, 1596, 1361, 1236, 1190, 1171,

1147, 1088, 1054, 812 cm-1

.

240

1-[1-[(4-Methylphenyl)sulfonyl]-1H-pyrrol-2-yl]but-2-yn-1-one (364):

A mixture of propargyl alcohol 363 (4.7 g, 16.2 mmol), IBX (11.4 g, 40.5 mmol), and

EtOAc (16 mL) were heated at reflux for 5 hours, under an atmosphere of argon gas.

After heating for this period of time, the reaction mixture was cooled to room

temperature, and then filtered through a plug of silica which was eluted with EtOAc.

Concentration of the eluted solvent, under reduced pressure, gave ketone 364 as a pure

orange solid (4.2 g, 91% yield, Rf = 0.31 in 20:80 EtOAc/hexane). (364): 1H NMR

(600.13 MHz, CDCl3): δ = 7.90-7.88 (m, 2H, 2 × ArH), 7.82 (dd, J = 1.8 and 3.6 Hz,

1H, C=CH), 7.31 (dd, J = 2.4 and 4.2 Hz, 1H, C=CH), 7.29-7.28 (m, 2H, 2 × ArH), 6.35

(dd, J = 1.8 and 3.6 Hz, 1H, C=CH), 2.39 (s, 3H, CH3), 2.00 (s, 3H, CH3); 13

C NMR

(150.9 MHz, CDCl3): δ = 164.6 (C=O), 145.2 (C), 135.3 (C), 133.7 (C), 131.4 (CH),

129.4 (CH), 128.7 (CH), 128.5 (CH), 110.8 (CH), 89.3 (C), 78.8 (C), 21.8 (CH3), 4.1

(CH3); HRMS (APCI): calc. for C15H14NO3S [M + H]+ 288.0694, found 288.0699; IR

(neat): ν = 3133, 2242, 2205, 1668, 1629 (C=O), 1594, 1537, 1423, 1406, 1362, 1341,

1306, 1256, 1205, 1188, 1167 cm-1

.

(2E)-3-Iodo-1-[1-[(4-methylphenyl)sulfonyl]-1H-pyrrol-2-yl]but-2-en-1-one (365);

(2Z)-3-iodo-1-[1-[(4-methylphenyl)sulfonyl]-1H-pyrrol-2-yl]but-2-en-1-one (327):

A mixture of alkyne 364 (1.13 g, 3.93 mmol), LiI (1.71 g, 12.8 mmol), CH3CN

(5.6 mL), and glacial AcOH (2 mL, 2.10 g, 34.9 mmol) were stirred at 70°C in a flame-

dried flask, under an atmosphere of argon gas, for 24 hours. After this time, the reaction

mixture was diluted with toluene (10 mL), and concentrated to remove the CH3CN. The

reaction mixture was then diluted with 9% w/w aq NaHCO3 (5 mL) and EtOAc (30

mL), and the aqueous and organic layers were separated. The aqueous layer was

241

extracted further with portions of EtOAc (2 × 30 mL), then the combined organic

extracts were dried (MgSO4), filtered, and concentrated under reduced pressure to give a

crude solid. The crude solid was subjected to flash column chromatography on silica gel

to (5:95 → 10:90 EtOAc/hexane) to give vinyl iodides 327 (644 mg, 39% yield, Rf =

0.64 in 20:80 EtOAc/hexane) and 365 (755 mg, 46% yield, Rf = 0.44 in 20:80

EtOAc/hexane). (365): 1H NMR (600.13 MHz, CDCl3): δ = 7.92-7.91 (m, 2H, 2 ×

ArH), 7.79 (dd, J = 1.8 and 3.0 Hz, 1H, C=CH), 7.32-7.30 (m, 2H, 2 × ArH), 7.29 (dd, J

= 1.8 and 3.0 Hz, 1H, C=CH), 6.98 (dd, J = 1.8 and 3.6 Hz, 1H, C=CH), 6.34 (dd, J =

3.0 and 3.6 Hz, 1H, C=CH), 2.88 (d, J = 1.8 Hz, 3H, CH3), 2.42 (s, 3H, CH3); 13

C NMR

(150.9 MHz, CDCl3): δ = 176.7 (C=O), 145.0 (C), 136.5 (CH), 136.0 (C), 133.7 (C),

130.8 (CH), 129.5 (CH), 128.6 (CH), 123.7 (CH), 119.6 (C), 110.7 (CH), 31.8 (CH3),

21.8 (CH3); HRMS (APCI): calc. C15H15NO3SI [M + H]+ 415.9817, found 415.9833;

IR (neat): ν = 3145, 1645 (C=O), 1579, 1433, 1351, 1305, 1251, 1196, 1182 cm-1

.

(327): 1H NMR (600.13 MHz, CDCl3): δ = 7.96 (app d, 2H, 2 × ArH), 7.80 (dd, J = 1.8

and 3.6 Hz, 1H, C=CH), 7.31 (app d, 2H, 2 × ArH), 6.97 (dd, J = 1.8 and 3.6 Hz, 1H,

C=CH), 6.86 (dd, J = 1.2 and 3.0 Hz, 1H, C=CH), 6.33 (dd, J = 3.0 and 3.6 Hz, 1H,

C=CH), 2.71 (d, J = 1.8 Hz, 3H, CH3), 2.42 (s, 3H, CH3); 13

C NMR (150.9 MHz,

CDCl3): δ = 178.2 (C), 145.1 (C), 135.7 (C), 133.4 (C), 130.7 (CH), 130.6 (CH), 129.5

(CH), 128.8 (CH), 124.0 (CH), 110.6 (CH), 109.3 (C), 36.3 (CH3), 21.8 (CH3); HRMS

(APCI): calc. C15H15NO3SI [M + H]+ 415.9817, found 415.9824; IR (neat): ν = 3147,

1661, 1597, 1541, 1493, 1437, 1403, 1352, 1293, 1258, 1192, 1166, 1140, 1090, 1062,

1004, 945 cm-1

.

(±)-5-Ethynyl-2,2,4-trimethyl-4-(4-methylpent-3-en-1-yl)-1,3-dioxolane (358):

A mixture of dibromo alkene 356 (1.78 g, 4.7 mmol) and THF (10 mL) was cooled to

-78°C in a flame dried flask, under an atmosphere of argon gas. To this cooled mixture

was added n-BuLi (6.2 mL, 1.6 M, 9.9 mmol), in one portion. The resulting mixture

was stirred at -78°C for 30 minutes. After this time, the reaction mixture was quenched

with 37% w/w aq NH4Cl (6 mL), diluted with Et2O (30 mL), and warmed to room

temperature. The reaction mixture was filtered through silica gel (eluted with Et2O) and

242

concentrated under reduced pressure to give a crude oil. The crude oil was subjected to

column chromatography (1:99 EtOAc/hexane) to give alkyne 358 as a colourless oil

(758 mg, 73% yield, Rf = 0.81 in 5:95 EtOAc/hexane). (358): 1H NMR (600.13 MHz,

CDCl3): δ = 5.13-5.10 (m, 1H, (CH3)2=CH), 4.44 (d, J = 2.4 Hz, O-CH), 2.53 (d, J = 2.4

Hz, C C-H), 2.17-2.11 (m, 1H, CH2-CH2), 2.09-2.01 (m, 1H, CH2-CH2), 1.77-1.70 (m,

1H, CH2-CH2), 1.66 (s, 3H, CH3), 1.63-1.56 (m, 1H, CH2-CH2), 1.60 (s, 3H, CH3), 1.46

(s, 3H, CH3), 1.35 (s, 3H, CH3), 1.31 (s, 3H, CH3); 13


131.6 (C),124.4 (CH), 109.3 (C),83.0 (C),78.0 (C),76.4 (CH), 74.8 (CH), 37.0 (CH2),

28.4 (CH3), 27.2 (CH3), 25.8 (CH3), 23.4 (CH3), 22.0 (CH2), 17.7 (CH3); HRMS (EI):

calc. C14H23O2 [M + H]+ 223.1698, found 223.1667; IR (neat): ν = 2983, 2932, 1615,

1455, 1377, 1218, 1120, 1088, 1051, 990, 919, 877, 822, 761 cm-1

.

243

5.5 Biological evaluation experimental for Chapter 2

Cell culture: Tumourigenic and non-tumourigenic LPCs were generated from p53-null

mice as previously described.150

Both LPC lines were cultured in Williams’ E medium

(Sigma–Aldrich) supplemented with 5% fetal calf serum (FCS), 30 ngmL-1

IGF-II

(GroPep, Adelaide, Australia), 20 ngmL-1

epidermal growth factor (EGF) (BD

Biosciences), 10 mgmL-1

insulin (Eli Lilly), 2 mm glutamine (Sigma–Aldrich), 2.5

mgmL-1

fungizone (Invitrogen), 44.8 ngmL-1

penicillin and 675 ngmL-1

streptomycin

(Invitrogen) at 37.8°C, 5% CO2. For experiments, the cells were inoculated into 96-well

plates (Nunc) at a density of 2000 cells well-1

.

The Cellscreen system: CellscreenTM is a product of Innovatis AG (Bielefeld,

Germany), which facilitates real-time analysis of cell growth by image capture followed

by analysis of the area occupied by cells. Growth of LPCs has been verified previously.3

Growth data from experiments were plotted on a log linear graph to determine the

window of log-phase growth and doubling time (h). For each culture doubling time was

determined by the equation h = t/n, for which t is the time of exponential growth and n

is the number of population doublings.

244

245

Chapter 6

Bibliography

246

247

(1) Nakamura, N.; Hirakawa, A.; Gao, J.-J.; Kakuda, H.; Shiro, M.; Komatsu, Y.;

Sheu, C.-c.; Hattori, M. Journal of Natural Products 2003, 67, 46.

(2) Wu, M.-D.; Cheng, M.-J.; Wang, B.-C.; Yech, Y.-J.; Lai, J.-T.; Kuo, Y.-H.;

Yuan, G.-F.; Chen, I.-S. Journal of Natural Products 2008, 71, 1258.

(3) Viebahn, C. S.; Tirnitz-Parker, J. E. E.; Olynyk, J. K.; Yeoh, G. C. T. European

Journal of Cell Biology 2006, 85, 1265.

(4) Kim, H.-J.; Vinale, F.; Ghisalberti, E. L.; Worth, C. M.; Sivasithamparam, K.;

Skelton, B. W.; White, A. H. Phytochemistry 2006, 67, 2277.

(5) Jiang, M.-Y.; Zhang, L.; Liu, R.; Dong, Z.-J.; Liu, J.-K. Journal of Natural

Products 2009, 72, 1405.

(6) Macherla, V. R.; Liu, J.; Bellows, C.; Teisan, S.; Nicholson, B.; Lam, K. S.;

Potts, B. C. M. Journal of Natural Products 2005, 68, 780.

(7) Buckingham, J. Dictionary of natural products; Chapman & Hall: London, New

York, 1994.

(8) Ji, H.-F.; Li, X.-J.; Zhang, H.-Y. EMBO reports 2009, 10, 194.

(9) Dias, D. A.; Urban, S.; Roessner, U. Metabolites 2012, 2.

(10) Yun, B.-W.; Yan, Z.; Amir, R.; Hong, S.; Jin, Y.-W.; Lee, E.-K.; Loake, G. J.

Biotechnology and Genetic Engineering Reviews 2013, 28, 47.

(11) Leroi-Gourhan, A. Science 1975, 190, 562.

(12) Nakanishi, K. Comprehensive Natural Products Chemistry; Elsevier Science

Ltd. , 1999.

(13) Firn, R. Nature's Chemicals: The Natural Products that shaped our world;

Oxford Scholarship, 2009.

(14) Ji, H.-F.; Li, X.-J.; Zhang, H.-Y. 2009, 10, 194.

(15) Wöhler, F. Annalen der Physik und Chemie 1828.

(16) Barton, D. H. R.; Zard, S. Z. Pure and Applied Chemistry 1986, 58, 675.

(17) Nicolaou, K. C.; Snyder, S. A. Proceedings of the National Academy of Sciences

of the United States of America 2004, 101, 11929.

(18) Nicolaou, K. C.; Harrison, S. T.; Chen, J. S. Synthesis 2009, 2009, 33.

(19) Shenvi, R. A.; O’Malley, D. P.; Baran, P. S. Accounts of Chemical Research

2009, 42, 530.

(20) Nicolaou, K. C.; Snyder, S. A. Angewandte Chemie International Edition 2005,

44, 1012.

(21) J., P. P.; B., C. J. Annales de chimie et de physique 1818, 8.

(22) J., P. P.; B., C. J. Annales de chimie et de physique 1819, 10.

(23) Cannon, J. S.; Overman, L. E. Angewandte Chemie International Edition 2012,

51, 4288.

(24) Briggs, L. H.; Openshaw, H. T.; Robinson, R. Journal of the Chemical Society

(Resumed) 1946, 0, 903.

(25) Smith, G. F. In The Alkaloids: Chemistry and Physiology; Manske, R. H. F.,

Ed.; Academic Press: 1965; Vol. Volume 8, p 591.

(26) Batchelor, F. R.; Doyle, F. P.; Nayler, J. H. C.; Rolinson, G. N. Nature 1959,

183, 257.

(27) Ulrich, H. Chemistry and Technology of Carbodiimides; John Wiley & Sons

2007.

(28) Flack, H. D. Acta Cryst. 2009, A65, 371.

(29) Gordaliza, M. Clinical and Translational Oncology 2007, 9, 767.

(30) da Rocha, A. B.; Lopes, R. M.; Schwartsmann, G. Current Opinion in

Pharmacology 2001, 1, 364.

(31) Newman, D. J.; Cragg, G. M. Journal of Natural Products 2007, 70, 461.

(32) Newman, D. J.; Cragg, G. M.; Snader, K. M. Journal of Natural Products 2003,

66, 1022.

248

(33) Nature Reviews Drug Discovery 2009, 8, 678.

(34) Lombardino, J. G.; Lowe, J. A. Nature Reviews Drug Discovery 2004, 3, 853.

(35) Swinney, D. C.; Anthony, J. Nature Reviews Drug Discovery 2011, 10, 507.

(36) Drews, J. Science 2000, 287, 1960.

(37) Li, J. W.-H.; Vederas, J. C. Science 2009, 325, 161.

(38) Hughes, J. P.; Rees, S.; Kalindjian, S. B.; Philpott, K. L. British Journal of

Pharmacology 2011, 162, 1239.

(39) Paul, S. M.; Mytelka, D. S.; Dunwiddie, C. T.; Persinger, C. C.; Munos, B. H.;

Lindborg, S. R.; Schacht, A. L. Nature Reviews Drug Discovery 2010, 9, 203.

(40) Wani, M. C.; Taylor, H. L.; Wall, M. E.; Coggon, P.; McPhail, A. T. Journal of

the American Chemical Society 1971, 93, 2325.

(41) Nadeem, M.; Rikhari, H. C.; Kumar, A.; Palni, L. M. S.; Nandi, S. K.

Phytochemistry 2002, 60, 627.

(42) Ganem, B.; Franke, R. R. The Journal of Organic Chemistry 2007, 72, 3981.

(43) Stephenson, F. Florida State University Research in Review 2002, 12

(44) David, K.; Dingemanse, E.; Freud, J. Biological Chemistry 1935, 233.

(45) Endo, A. Journal of Lipid Research 1992, 33, 1569.

(46) Blaskó, G.; Cordell, G. A. Heterocycles 1988, 27.

(47) Hegedus, L. S. Transition Metals in the Synthesis of Complex Organic

Molecules; University Science Books: California, 1999.

(48) Beller, M.; Bolm, C. Transition Metals for Organic Synthesis: Building Blocks

and Fine Chemicals, Second Revised and Enlarged Edition; WILEY-VCH,

2004.

(49) Jira, R. Angewandte Chemie International Edition 2009, 48, 9034.

(50) Negishi, E.-i. Handbook of Organopalladium Chemistry for Organic Synthesis;

John Wiley & Sons, 2003.

(51) Nicolaou, K. C.; Bulger, P. G.; Sarlah, D. Angewandte Chemie International

Edition 2005, 44, 4442.

(52) Powers, D. C.; Ritter, T. Topics in Organometallic Chemistry 2011, 35, 129.

(53) King, A. O.; Okukado, N.; Negishi, E.-i. Journal of the Chemical Society,

Chemical Communications 1977, 0, 683.

(54) Matos, K.; Soderquist, J. A. The Journal of Organic Chemistry 1998, 63, 461.

(55) Martin, V. S.; Woodard, S. S.; Katsuki, T.; Yamada, Y.; Ikeda, M.; Sharpless, K.

B. Journal of the American Chemical Society 1981, 103, 6237.

(56) Miyaura, N.; Yamada, K.; Suzuki, A. Tetrahedron Letters 1979, 20, 3437.

(57) Miyaura, N.; Suzuki, A. Journal of the Chemical Society, Chemical

Communications 1979, 0, 866.

(58) Miyaura, N.; Suzuki, A. Chemical Reviews 1995, 95, 2457.

(59) Suzuki, A. Accounts of Chemical Research 1982, 15, 178

(60) Sonogashira, K. Journal of Organometallic Chemistry 2002, 653, 46.

(61) Jutand, A. The-Mizoroki-Heck reaction; John Wiley and Sons, 2009.

(62) Heck, R. F.; Nolley, J. P. The Journal of Organic Chemistry 1972, 37, 2320.

(63) Heck, R. F. Journal of the American Chemical Society 1969, 91.

(64) Heck, R. F. Journal of the American Chemical Society 1968, 90.

(65) Amatore, C.; Azzabi, M.; Jutand, A. Journal of the American Chemical Society

1991, 113, 8375.

(66) Amatore, C.; Pfluger, F. Organometallics 1990, 9, 2276.

(67) Amatore, C.; Jutand, A.; Khalil, F.; M'Barki, M. A.; Mottier, L. Organometallics

1993, 12, 3168.

(68) Amatore, C.; Bahsoun, A. A.; Jutand, A.; Mensah, L.; Meyer, G.; Ricard, L.

Organometallics 2005, 24, 1569.

(69) Tsuji, J. Tetrahedron 1986, 42, 4361.

249

(70) Amatore, C.; Jutand, A.; M'Barki, M. A. Organometallics 1992, 11, 3009.

(71) Amatore, C.; Carre, E.; Jutand, A.; M'Barki, M. A.; Meyer, G. Organometallics

1995, 14, 5605.

(72) Smith, M. B.; March, J. March's Advanced Organic Chemistry; 5 ed.; John

Wiley & Sons, Inc: New York, Chichester, Weinheim, Brisbane, Singapore,

Toronto, 2001.

(73) Albaneze-Walker, J.; Raju, R.; Vance, J. A.; Goodman, A. J.; Reeder, M. R.;

Liao, J.; Maust, M. T.; Irish, P. A.; Espino, P.; Andrews, D. R. Organic Letters

2009, 11, 1463.

(74) Casares, J. A.; Espinet, P.; Fuentes, B.; Salas, G. Journal of the American

Chemical Society 2007, 129, 3508.

(75) Milstein, D.; Stille, J. K. Journal of the American Chemical Society 1978, 100,

3636.

(76) Erdik, E. Tetrahedron 1992, 48, 9577

(77) Negishi, E.; T.Takahashi; Babu, S.; Horn, D. E. V.; Okukado, N. Journal of the

American Chemical Society 1987, 109, 2393.

(78) Rappoport, Z.; Marek, I. The Chemistry of Organozinc Compounds: R-Zn;

Wiley, 2006.

(79) Knochel, P.; Jones, P. Organozinc Reagents: A Practical Approach (The

Practical Approach in Chemistry Series); Oxford University Press: Oxford New

York, 1999.

(80) Knochel, P.; Singer, R. D. Chemical Reviews 1993, 93, 2117.

(81) Boudier, A.; Bromm, L. O.; Lotz, M.; P. Knochel Angewandte Chemie 2000,

112, 4584.

(82) III, A. B. S.; Beauchamp, T. J.; LaMarche, M. J.; Kaufman, M. D.; Y. Qiu, H.

A.; Jones, D. R.; Kobayashi, K. Journal of the American Chemical Society 2000,

122, 8654

(83) III, A. B. S.; Kaufman, M. D.; Beauchamp, T. J.; LaMarche, M. J.; Arimoto, H.

Org. Lett. 1999, 1, 1823

(84) Miyaura, N.; Suzuki, A. Chemical Reviews 1995, 95, 2457.

(85) Hall, D. G. Structure, Properties, and Preparation of Boronic Acid Derivatives.

Overview of Their Reactions and Applications; Wiley-VCH Verlag GmbH &

Co. KGaA, 2006.

(86) Kirchhoff, J. H.; Netherton, M. R.; Hills, I. D.; Fu, G. C. Journal of the


(87) Weir, R. J.; Fisher, R. S. Toxicol. Appl. Pharmacol. 1972, 23, 351.

(88) Suzuki, A. Journal of Organometallic Chemistry 1999, 576, 147.

(89) Ishiyama, T.; Abe, S.; Miyaura, N.; Suzuki, A. Chem. Lett. 1992, 691–694.

(90) Zhou, J.; Fu, G. C. Journal of the American Chemical Society 2004, 126, 1340

(91) Carrow, B. P.; Hartwig, J. F. Journal of the American Chemical Society 2011,

133, 2116.

(92) Wang, B.; Sun, H.-X.; Sun, Z.-H. Eur. J. Org. Chem. 2009, Short

Communication, 3688.

(93) Ishiyama, T.; Miyaura, N. The Chemical Record 2004, 3, 271.

(94) Takagi, J.; Takahashi, K.; Ishiyama, T.; Miyaura, N. Journal of the American


(95) Hobbs, P. D.; Upender, V.; Liu, J.; Pollart, D. J.; Thomas, D. W.; Dawson, M. I.

Chem. Commun. 1996, 923.

(96) Cassar, L. J. Organomet. Chem. 1975, 93, 253

(97) Dieck, H. A.; F. R. Heck J. Organomet. Chem. 1975, 93, 259.

(98) K. Sonogashira, Y. T., N. Hagihara, Tetrahedron Lett. 1975, 16, 4467.

250

(99) King, A.; Yasuda, N. In Organometallics in Process Chemistry; Springer Berlin

Heidelberg: 2004; Vol. 6, p 205.

(100) Negishi, E.; Anastasia, L. Chemical Reviews 2003, 103, 1979.

(101) Chinchilla, R.; Najera, C. Chemical Society Reviews 2011, 40, 5084.

(102) Smith, A. L.; Nicolaou, K. C. J. Med. Chem. 1996, 39, 2103.

(103) Taunton, J.; Wood, J. L.; Schreiber, S. L. Journal of the American Chemical

Society 1993, 115, 10378.

(104) Nicolaou, K. C.; Hummel, C. W.; Pitsinos, E. N.; Nakada, M.; Smith, A. L.;

Shibayama, K.; Saimoto, H. Journal of the American Chemical Society 1992,

114, 10082.

(105) Wipf, P.; Graham, T. H. Journal of the American Chemical Society 2004, 126,

15346.

(106) F., H. R. Accounts of Chemical Research 1979, 12.

(107) Heck, R. F. Org. React. 1982, 27, 345.

(108) Heck, R. F.; M., T. B., Ed.; Pergamon Press: Oxford, 1991; Vol. 4.

(109) Cabri, W.; Candiani, I. Accounts of Chemical Research 1995, 28.

(110) Mizoroki, T.; K. Mori, A. O. Bull. Chem. Soc. Jpn 1971, 44.

(111) Heck, R. F.; J. P. Nolley, J. J. Org. Chem. 1972, 37, , 2320.

(112) Dounay, A. B.; Overman, L. E. Chemical Reviews 2003, 103, 2945.

(113) Shibasaki, M.; Christopher, D. J. B.; Kojima, A. Tetrahedron 1997, 53, 737

(114) Shibasaki, M.; Vogl, E. M. J. Organomet. Chem. Commun. 1999, 576, 1.

(115) Negishi, E.; Coperet, C.; Ma, S.; Liou, S.-Y.; Liu, F. 1996, 96.

(116) Gibson, S. E.; Middleton, R. J. Contemp. Org. Synth. 1996, 3.

(117) Heck, R. F. Acc. Chem. Res 1979, 12, 146.

(118) Heck, R. F. Org. React. 1982, 27, 345.

(119) Beletskaya, I. P.; Cheprakov, A. V. Chemical Reviews 2000, 100, 3009.

(120) Link, J. T. Org. React. 2002, 60, 157.

(121) Negishi, E.; CopTret, C.; Ma, S.; Liou, S.-Y.; Liu, F. Chemical Reviews 1996,

96, 365.

(122) Tietze, L. F.; Schneider, G.; Wölfling, J.; Nöbel, T.; Wulff, C.; Schubert, I.;

Rübeling, A. Angewandte Chemie International Edition 1998, 37, 2469.

(123) Drews, J. 2000, 287.

(124) Bleicher, K. H.; Bohm, H.-J.; Muller, K.; Alanine, A. I. Nature Reviews Drug

Discovery 2003, 2, 369.

(125) Feher, M.; Schmidt, J. M. Journal of Chemical Information and Computer

Sciences 2002, 43, 218.

(126) von Nussbaum, F.; Brands, M.; Hinzen, B.; Weigand, S.; Häbich, D.

Angewandte Chemie International Edition 2006, 45, 5072.

(127) Singh, S. S. Current Drug Metabolism 2006, 7, 165.

(128) Lee, J. A.; Uhlik, M. T.; Moxham, C. M.; Tomandl, D.; Sall, D. J. Journal of

Medicinal Chemistry 2012, 55, 4527.

(129) Nussbaum, F. v.; Brands, M.; Hinzen, B.; Weigand, S.; Habich, D. Angewandte

Chemie International Edition 2006, 45, 5072.

(130) Takenaka, T. BJU International 2001, 88, 7.

(131) Ghose, A. K.; Viswanadhan, V. N.; Wendoloski, J. J. Journal of Combinatorial

Chemistry 1998, 1, 55.

(132) Keserű, G. M.; Makara, G. M. Drug Discovery Today 2006, 11, 741.

(133) Dong, L.; Schill, H.; Grange, R. L.; Porzelle, A.; Johns, J. P.; Parsons, P. G.;

Gordon, V. A.; Reddell, P. W.; Williams, C. M. Chemistry – A European

Journal 2009, 15, 11307.

(134) Wess, G.; Urmann, M.; Sickenberger, B. Angewandte Chemie International

Edition 2001, 40, 3341.

251

(135) Fabricant, D. S.; Farnsworth, N. R. Environmental Health Perspectives, 109.

(136) Kuete, V.; Wabo, H. K.; Eyong, K. O.; Feussi, M. T.; Wiench, B.; Krusche, B.;

Tane, P.; Folefoc, G. N.; Efferth, T. PLoS ONE 2011, 6, e21762.

(137) Hsu, Y.-L.; Kuo, Y.-C.; Kuo, P.-L.; Ng, L.-T.; Kuo, Y.-H.; Lin, C.-C. Cancer

Letters 2005, 221, 77.

(138) Song, T.-Y.; Yen, G.-C. Journal of Agricultural and Food Chemistry 2002, 50,

3322.

(139) Hseu, Y.-C.; Chang, W.-C.; Hseu, Y.-T.; Lee, C.-Y.; Yech, Y.-J.; Chen, P.-C.;

Chen, J.-Y.; Yang, H.-L. Life Sciences 2002, 71, 469.

(140) Ao, Z.-H.; Xu, Z.-H.; Lu, Z.-M.; Xu, H.-Y.; Zhang, X.-M.; Dou, W.-F. Journal

of Ethnopharmacology 2009, 121, 194.

(141) J., C. J.; J., L. W. J. Nat. Prod. 2007, 70.

(142) C., C. C.; J., S. Y.; D., L. R.; Y., S. Y. 2006, 69, 689.

(143) Smalley, K. S. M.; Xiao, M.; Villanueva, J.; Nguyen, T. K.; Flaherty, K. T.;

Letrero, R.; Van Belle, P.; Elder, D. E.; Wang, Y.; Nathanson, K. L.; Herlyn, M.

Oncogene 2008, 28, 85.

(144) Keating, G.; Santoro, A. Drugs 2009, 69, 223.

(145) Wilhelm, S. M.; Adnane, L.; Newell, P.; Villanueva, A.; Llovet, J. M.; Lynch,

M. Molecular Cancer Therapeutics 2008, 7, 3129.

(146) V., K.; N., F.; A., A. Robbins & Cotran Pathologic Basis of Disease; 7 ed.;

Saunders, 2003.

(147) Knight, B.; Matthews, V. B.; Akhurst, B.; Croager, E. J.; Klinken, E.; Abraham,

L. J.; Olynyk, J. K.; Yeoh, G. Immunol. Cell Biol. 2005, 83, 364.

(148) Knight, B.; Yeoh, G. C.; Husk, K. L.; Ly, T.; Abraham, L. J.; Yu, C.; Rhim, J.

A.; N.Fausto J. Exp. Med. 2000, 192, 1809.

(149) Dumble, M. L.; Croager, E. J.; Yeoh, G. C. T.; Quail, E. A. Carcinogenesis

2002, 23, 435.

(150) Dumble, M. L.; Knight, B.; Quail, E. A.; Yeoh, G. C. T. Cell Growth Differ.

2001, 12, 223.

(151) Isobe, M.; Emanuel, B. S.; Givol, D.; Oren, M.; Croce, C. M. Nature 1986, 320,

84.

(152) Kern, S.; Kinzler, K.; Bruskin, A.; Jarosz, D.; Friedman, P.; Prives, C.;

Vogelstein, B. Science 1991, 252, 1708.

(153) McBride, O. W.; Merry, D.; Givol, D. Proceedings of the National Academy of

Sciences 1986, 83, 130.

(154) Matlashewski, G.; Lamb, P.; Pim, D.; Peacock, J.; Crawford, L.; Benchimol, S.

EMBO reports 1984, 3, 3257.

(155) Read, A. P.; Strachan, T. In Human molecular genetics; 2 ed.; Wiley: New

York, 1999.

(156) Tawney, P. O.; Snyder, R. H.; Conger, R. P.; Leibrand, K. A.; Stiteler, C. H.;

Williams, A. R. Chemical Reviews 1960, 26, 15.

(157) Hargreaves, M. K.; Pritchard, J. G.; Dave, H. R. Chemical Reviews 1970, 70,

439.

(158) GORDON, A. J.; EHRENKAUFER, R. L. E. J. Org. Chern 1970.

(159) Shah, K. R.; Blanton, C. D. The Journal of Organic Chemistry 1982, 47, 502.

(160) Marrian, D. H. Journal of the Chemical Society (Resumed) 1949, 0, 1515.

(161) Katritzky, A. R.

(162) Lubczak, J. Open Journal of Physical Chemistry 2012, 2, 97.

(163) Salewska, N.; Boros-Majewska, J.; Łącka, I.; Chylińska, K.; Sabis, M.;

Milewski, S.; Milewska1, M. J. Journal of Enzyme Inhibition and Medicinal

Chemistry 2012, 27, 117.

252

(164) Putri, S. P.; Kinoshita, H.; Ihara, F.; Igarashi, Y.; Nihira, T. Journal of Natural

Products 2009, 72, 1544.

(165) Birkinshaw, J. H.; Kalyanpur, M. G.; Stickings, C. E. Biochem. J. 1963, 86, 237.

(166) Stewart, S. G.; Polomska, M. E.; Lim, R. W. Tetrahedron Letters 2007, 48,

2241.

(167) Stewart, S. G.; Ho, L. A.; Polomska, M. E.; Percival, A. T.; Yeoh, G. C. T.

ChemMedChem 2009, 4, 1657.

(168) Jin, L.; Agag, T.; Ishida, H. European Polymer Journal 2010, 46, 354.

(169) Kalgutkar, A. S.; Crews, B. C.; Marnett, L. J. Journal of Medicinal Chemistry

1996, 39, 1692.

(170) Zhang, X.; Chen, G.-C.; Collins, A.; Jacobson, S.; Morganelli, P.; Dar, Y. L.;

Musa, O. M. Journal of Polymer Science Part A: Polymer Chemistry 2009, 47,

1073.

(171) A.-M, A.; Abdel-Aziz European Journal of Medicinal Chemistry 2007, 42.

(172) Benjamin, E.; Hijji, Y. Molecules 2008, 13.

(173) COTTER, R. J.; SAUERS, C. K.; WHELAN, J. M. J. Org. Chem. 1960, 26.

(174) Eberson, L.; Welinder, H. Journal of the American Chemical Society 1971, 93,

5821.

(175) Chen, X.; Zheng, Y.; Shen, Y. Chemical Reviews 2007, 107, 1777.

(176) Geethangili, M.; Tzeng, Y.-M. Evidence-Based Complementary and Alternative

Medicine 2011, 2011.

(177) Baag, M. M.; Argade, N. P. Synthesis 2006, 2006, 1005.

(178) Dubernet, M.; Caubert, V.; Guillard, J.; Viaud-Massuard, M.-C. Tetrahedron

2005, 61, 4585.

(179) Feuer, H.; Hooz, J. In The Ether Linkage (1967); John Wiley & Sons, Ltd.:

2010, p 445.

(180) Couture, A.; Deniau, E.; Grandclaudon, P.; Lebrun, S. Tetrahedron: Asymmetry

2003, 14, 1309.

(181) Brierley, J. B.; McCoubrey, A. British Journal of Pharmacology and

Chemotherapy 1953, 8, 366.

(182) An, P.; Shi, Z.-F.; Dou, W.; Cao, X.-P.; Zhang, H.-L. Organic Letters 2010, 12,

4364.

(183) Denmark, S. E.; Smith, R. C.; Tymonko, S. A. Tetrahedron 2007, 63, 5730.

(184) Catanescu, C. O.; Wu, S.-T.; Chien, L.-C. Liquid Crystals 2004, 31, 541.

(185) Ebisawa, M.; Ueno, M.; Oshima, Y.; Kondo, Y. Tetrahedron Letters 2007, 48,

8918.

(186) Kim, J.; Kim, Y. K.; Park, N.; Hahn, J. H.; Ahn, K. H. The Journal of Organic

Chemistry 2005, 70, 7087.

(187) Miller, B.; Margulies, H. The Journal of Organic Chemistry 1965, 30, 3895.

(188) Cladingboel, D. E. Org. Proc. Res. Devel. 2000, 4, 153.

(189) Zenk, R.; Partzsch, S. Chim. Oggi 2003, 70.

(190) Fukuda, T.; Sudo, E.-i.; Shimokawa, K.; Iwao, M. Tetrahedron 2008, 64, 328.

(191) Cui, J.; Liu, A.; Guan, Y.; Zheng, J.; Shen, Z.; Wan, X. Langmuir 2009, 26,

3615.

(192) Kuivila, H. G.; Nahabedian, K. V. Journal of the American Chemical Society

1961, 83, 2159.

(193) Kuivila, H. G.; Nahabedian, K. V. Journal of the American Chemical Society

1961, 83, 2164.

(194) Nahabedian, K. V.; Kuivila, H. G. Journal of the American Chemical Society

1961, 83, 2167.

(195) Soloway, A. H.; Whitman, B.; Messer, J. R. J. Pharm. Exp. Ther. 1960, 129,

310.

253

(196) E, L. D.; S, S. M.; M, S. R. In Millennium Pharmaceuticals, Inc., USA Office, E.

P., Ed. USA, 2003; Vol. WO 2003022214.

(197) Murata, M.; Watanabe, S.; Masuda, Y. The Journal of Organic Chemistry 1997,

62, 6458.

(198) Kawamorita, S.; Ohmiya, H.; Iwai, T.; Sawamura, M. Angewandte Chemie

International Edition 2011, 50, 8363.

(199) Khanna, S.; Burudkar, S.; Bajaj, K.; Shah, P.; Keche, A.; Ghosh, U.; Desai, A.;

Srivastava, A.; Kulkarni-Almeida, A.; Deshmukh, N. J.; Dixit, A.; Brahma, M.

K.; Bahirat, U.; Doshi, L.; Nemmani, K. V. S.; Tannu, P.; Damre, A.; B-Rao, C.;

Sharma, R.; Sivaramakrishnan, H. Bioorganic & Medicinal Chemistry Letters

2012, 22, 7543.

(200) Wang, Y.; Liu, Y.; Luo, J.; Qi, H.; Li, X.; Nin, M.; Liu, M.; Shi, D.; Zhu, W.;

Cao, Y. Dalton Transactions 2011, 40, 5046.

(201) Branch, G. E. K.; Yabroff, D. L.; B. Bettmann Journal of the American


(202) Bettman, B.; Branch, G. E. K.; Yabroff, D. L. Journal of the American Chemical

Society 1934, 56, 1865.

(203) Torssell, K.; McLendon, J. H.; Somers, G. F. Acta Scand. Chem. 1958, 12, 1373.

(204) Singhal, R. P.; Ramamurthy, B.; Govindraj, N.; Y. Sarwar J. Chromatogr. 1991,

543, 17.

(205) Banwell, M. G.; Flynn, B. L.; Stewart, S. G. The Journal of Organic Chemistry

1999, 64, 6118.

(206) Milstien, S.; Cohen, L. A. Proceedings of the National Academy of Sciences

1970, 67, 1143.

(207) Bruice, T. C.; Bradbury, W. C. Journal of the American Chemical Society 1965,

87, 4846.

(208) Bruice, T. C.; Pandit, U. K. Journal of the American Chemical Society 1960, 82,

5858.

(209) Ficken, G. E.; Linstead, R. P. Journal of the Chemical Society (Resumed) 1952,

4846.

(210) Meessen, J. H. In Ullmann's Encyclopedia of Industrial Chemistry; Wiley-VCH

Verlag GmbH & Co. KGaA: 2000.

(211) Davidson, D.; Skovronek, H. Journal of the American Chemical Society 1958,

80, 376.

(212) Tamaru, Y.; Nichols, P. J. In Encyclopedia of Reagents for Organic Synthesis;

John Wiley & Sons, Ltd: 2001.

(213) Watson, D. J.; Dowdy, E. D.; Li, W.-S.; Wang, J.; Polniaszek, R. Tetrahedron

Letters 2001, 42, 1827.

(214) Landzettel, W. J.; Hargis, K. J.; Caboot, J. B.; Adkins, K. L.; Strein, T. G.;

Veening, H.; Becker, H.-D. Journal of Chromatography A 1995, 718, 45.

(215) Coates1*, J. Applied Spectroscopy Reviews 2001, 36, 299.

(216) Wang, Y.-L. In Methods in Cell Biology; Yu-Li Wang, D. L. T., Jeon, K. W.,

Eds.; Academic Press: 1988; Vol. Volume 29, p 1.

(217) Small, J. V.; Rottner, K.; Hahne, P.; Anderson, K. I. Microscopy Research and

Technique 1999, 47, 3.

(218) Selvin, P. R. Nature Structural Biology 2000, 7, 730.

(219) Y, K. Angewandte Chemie 1977, 16, 137.

(220) Sirk, S. J.; Olafsen, T.; Barat, B.; Bauer, K. B.; Wu, A. M. Bioconjugate

Chemistry 2008, 19, 2527.

(221) Hendricks, R. T.; Sherman, D.; Strulovici, B.; Broka, C. A. Bioorganic &

Medicinal Chemistry Letters 1995, 5, 67.

(222) Ridley, J.; Zerner, M. Theoretica Chimica Acta 1973, 32, 111.

254

(223) GII, J.; WR, J.; C, C.; WR, B. J Phys Chem 1985, 89, 298.

(224) Van Gompel, J. A.; Schuster, G. B. The Journal of Physical Chemistry 1989, 93,

1292.

(225) Takadate, A.; Masuda, T.; Murata, C.; Isobe, A.; Shinohara, T.; Irikura, M.;

Goya, S. Analytical Sciences 1997, 13, 753.

(226) Matsunaga, H.; Santa, T.; Iida, T.; Fukushima, T.; Homma, H.; Imai, K. Analyst

1997, 122, 931.

(227) R, S.; T, H.; H, N.; M, O. J Chem Soc Perkin Trans 2 1997, 1711.

(228) Fabian, W. M. F.; Niederreiter, K. S.; Uray, G.; Stadlbauer, W. Journal of

Molecular Structure 1999, 477, 209.

(229) Hutchison, G. R.; Ratner, M. A.; Marks, T. J. The Journal of Physical Chemistry

A 2002, 106, 10596.

(230) Wang, B.-C.; Liao, H.-R.; Yeh, H.-C.; Wu, W.-C.; Chen, C.-T. Journal of

Luminescence 2005, 113, 321.

(231) Uchiyama, S.; Santa, T.; Imai, K. Journal of the Chemical Society, Perkin

Transactions 2 1999, 0, 569.

(232) Chachisvilis, M.; Chirvony, V. S.; Shulga, A. M.; Källebring, B.; Larsson, S.;

Sundström, V. The Journal of Physical Chemistry 1996, 100, 13857.

(233) Amati, M.; Lelj, F. The Journal of Physical Chemistry A 2003, 107, 2560.

(234) Chakraborty, A.; Kar, S.; Nath, D. N.; Guchhait, N. The Journal of Physical

Chemistry A 2006, 110, 12089.

(235) Uray, G.; Kelterer, A.-M.; Hashim, J.; Glasnov, T. N.; Oliver Kappe, C.; Fabian,

W. M. F. Journal of Molecular Structure 2009, 929, 85.

(236) Sheikhshoaie, I.; Belaj, F.; Fabian, W. M. F. Journal of Molecular Structure

2006, 794, 244.

(237) Cornelissen-Gude, C.; Rettig, W. The Journal of Physical Chemistry A 1999,

103, 4371.

(238) Xie, H.-d.; Ho, L.; Truelove, M.; Corry, B.; Stewart, S. Journal of Fluorescence

2010, 20, 1077.

(239) Marco-Contelles, J.; Molina, M. T.; Anjum, S. Chemical Reviews 2004, 104,

2857.

(240) Ichihara, A.; Kimura, R.; Oda, K.; Moriyasu, K.; Sakamura, S. Agricultural and

Biological Chemistry 1982, 46, 1879.

(241) Ichihara, A.; Moriyasu, K.; Sakamura, S. Agricultural and Biological Chemistry

1978, 42, 2421.

(242) Jin, M.-Y.; Hwang, G.-S.; Chae, H.-I.; Jung, S.-H.; Ryu, D.-H. Bulletin of the

Korean Chemical Society 2010, 31, 727.

(243) Li, C.; Pace, E. A.; Liang, M.-C.; Lobkovsky, E.; Gilmore, T. D.; Porco, J. A.

Journal of the American Chemical Society 2001, 123, 11308.

(244) Enhsen, A.; Karabelas, K.; Heerding, J. M.; Moore, H. W. The Journal of

Organic Chemistry 1990, 55, 1177.

(245) Sheehan, J. C.; Lawson, W. B.; Gaul, R. J. Journal of the American Chemical

Society 1958, 80, 5536.

(246) Kawakami, Y.; Hartman, S. E.; Kinoshita, E.; Suzuki, H.; Kitaura, J.; Yao, L.;

Inagaki, N.; Franco, A.; Hata, D.; Maeda-Yamamoto, M.; Fukamachi, H.; Nagai,

H.; Kawakami, T. Proceedings of the National Academy of Sciences 1999, 96,

2227.

(247) Anderson, M. G.; Rickards, R. W.; Lacey, E. Journal of Antibiotics 1999, 52,

1023.

(248) Garlaschelli, L.; Magistrali, E.; Vidari, G.; Zuffardi, O. Tetrahedron Letters

1995, 36, 5633.

(249) Miyashita, K.; Imanishi, T. Chemical Reviews 2005, 105, 4515.

255

(250) Shoji, M.; Hayashi, Y. European Journal of Organic Chemistry 2007, 2007,

3783.

(251) Sattler, I.; Thiericke, R.; Zeeck, A. Natural Product Reports 1998, 15, 221.

(252) Venkatasubbaiah, P.; Dyke, C. G. V.; Chilton, W. S. Mycologia 1992, 84, 715.

(253) Yamamoto, I.; Mizuta, E.; Henmi, T.; Yamano, T.; Yamatodani, S. Takeda

Kenkyushoho 1973, 32, 532.

(254) Kobayashi, A.; Ooe, K.; Yata, S.; Kawazu, K. Tennen Yuki Kagobutsu Toronkai

Koen Yoshishu 1989, 31, 388.

(255) Itoh, Y. M., Tomoko; Katayama, Toshiaki; Haneishi, Tatsuo; Arai, Mamoru

Journal of Antibiotics 1978, 31, 834.

(256) Hara, M.; Soga, S.; Shono, K.; Eishima, J.; Mizukami, T. Journal of Antibiotics

2001, 54, 182.

(257) Li, J. Y.; Harper, J. K.; Grant, D. M.; Tombe, B. O.; Bashyal, B.; Hess, W. M.;

Strobel, G. A. Phytochemistry 2001, 56, 463.

(258) Hookins, D. R.; Burns, A. R.; Taylor, R. J. K. European Journal of Organic

Chemistry 2011, 2011, 451.

(259) Freeman, J.; Ward, E. Molecular Plant Pathology 2004, 5, 235.

(260) Lebreton, L.; Gosme, M.; Lucas, P.; Guillerm-Erckelboudt, A.-Y.; Sarniguet, A.

Environmental Microbiology 2007, 9, 492.

(261) Daval, S.; Lebreton, L.; Gazengel, K.; Guillerm-Erckelboudt, A. Y.; Sarniguet,

A. Plant Pathology 2010, 59, 165.

(262) Nagata, T.; Ando, Y.; Hirota, A. Bioscience Biotechnology and Biochemistry

1992, 56, 810.

(263) Dong, L.; Gordon, V. A.; Grange, R. L.; Johns, J.; Parsons, P. G.; Porzelle, A.;

Reddell, P.; Schill, H.; Williams, C. M. Journal of the American Chemical

Society 2008, 130, 15262.

(264) Shoji, M. Bulletin of the Chemical Society of Japan 2007, 80, 1672.

(265) Wipf, P.; Coish, P. D. G. The Journal of Organic Chemistry 1999, 64, 5053.

(266) Wipf, P.; Kim, Y. The Journal of Organic Chemistry 1994, 59, 3518.

(267) Gould, S. J.; Shen, B.; Whittle, Y. G. Journal of the American Chemical Society

1989, 111, 7932.

(268) Magdziak, D.; Meek, S. J.; Pettus, T. R. R. Chemical Reviews 2004, 104, 1383.

(269) Hu, Y.; Li, C.; Kulkarni, B. A.; Strobel, G.; Lobkovsky, E.; Torczynski, R. M.;

Porco, J. A. Organic Letters 2001, 3, 1649.

(270) Jung, S. H.; Hwang, G.-S.; Lee, S. I.; Ryu, D. H. The Journal of Organic

Chemistry 2012, 77, 2513.

(271) Musso, H. Angewandte Chemie 1963, 75, 965.

(272) Dewar, M. J. S.; Nakaya, T. Journal of the American Chemical Society 1968, 90,

7134.

(273) Fetizon, M.; Balogh, V.; Golfier, M. The Journal of Organic Chemistry 1971,

36, 1339.

(274) Taub, D.; Kuo, C. H.; Slates, H. L.; Wendler, N. L. Tetrahedron 1963, 19, 1.

(275) Carrick, W. L.; Karapinka, G. L.; Kwiatkowski, G. T. The Journal of Organic

Chemistry 1969, 34, 2388.

(276) Schwartz, M. A.; Mami, I. S. Journal of the American Chemical Society 1975,

97, 1239.

(277) Brussee, J.; Jansen, A. C. A. Tetrahedron Letters 1983, 24, 3261.

(278) Pelter, A.; Ward, R. S. Tetrahedron 2001, 57, 273.

(279) Pelter, A.; Elgendy, S. M. A. Journal of the Chemical Society, Perkin

Transactions 1 1993, 1891.

(280) Uyanik, M.; Ishihara, K. Chemical Communications 2009, 2086.

256

(281) Kürti, L.; Szilágyi, L.; Antus, S.; Nógrádi, M. European Journal of Organic

Chemistry 1999, 1999, 2579.

(282) Pelter, A.; Elgendy, S. Tetrahedron Letters 1988, 29, 677.

(283) Rama Krishna, K. V.; Sujatha, K.; Kapil, R. S. Tetrahedron Letters 1990, 31,

1351.

(284) Kurti, L.; Herczegh, P.; Visy, J.; Simonyi, M.; Antus, S.; Pelter, A. Journal of

the Chemical Society, Perkin Transactions 1 1999, 0, 379.

(285) Fieser, L. F.; Fieser, M.; Wiley: New York, 1967; Vol. 1, p 983.

(286) Anderson, K. W.; Ikawa, T.; Tundel, R. E.; Buchwald, S. L. Journal of the


(287) Ulrich, H.; Rao, D. V.; Tucker, B.; Sayigh, A. A. R. The Journal of Organic

Chemistry 1974, 39, 2437.

(288) Katsuki, T.; Sharpless, K. B. Journal of the American Chemical Society 1980,

102, 5974.

(289) Finn, M. G.; Sharpless, K. B. Journal of the American Chemical Society 1991,

113, 113.

(290) Gao, Y.; Klunder, J. M.; Hanson, R. M.; Masamune, H.; Ko, S. Y.; Sharpless, K.

B. Journal of the American Chemical Society 1987, 109, 5765.

(291) Katsuki, T.; Martin, V. S. Org. React. 1996, 48, 1.

(292) Hill, J. G.; Sharpless, K. B.; Exon, C. M.; Regenye, R. Org. Syn. 1990, 7.

(293) Itoh, T.; Jitsukawa, K.; Kaneda, K.; Teranishi, S. Journal of the American


(294) Zhang, W.; Yamamoto, H. Journal of the American Chemical Society 2006, 129,

286.

(295) McDonald, R. N.; Steppel, R. N.; Dorsey, J. E. Org. Synth. 1988, 6.

(296) Tamura, Y.; Yakura, T.; Tohma, H.; Ki-kuchi, K.; Kita, Y. Synthesis 1989,

1989, 126.

(297) Porter, M. J.; Skidmore, J. In Organic Reactions; John Wiley & Sons, Inc.:

2004.

(298) Nemoto, T.; Ohshima, T.; Yamaguchi, K.; Shibasaki, M. Journal of the

American Chemical Society 2001, 123.

(299) Jacques, O.; Richards, S. J.; Jackson, R. F. W. Chem. Commun. 2001.

(300) Allen, J. V.; Drauz, K. H.; Flood, R. W.; Roberts, S. M.; Skidmore, J.

Tetrahedron Lett. 1999, 40.

(301) Watanabe, S.; Kobayashi, Y.; Arai, T.; Sasai, H.; Bougauchi, M.; Shibasaki, M.

Tetrahedron Lett. 1998, 39.

(302) Omura, K. Synthetic Communications: An International Journal for Rapid

Communication of Synthetic Organic Chemistry 2000, 30, 877

(303) Sefkow, M.; Kaatz, H. Tetrahedron Letters 1999, 40, 6561.

(304) , S.

Tetrahedron: Asymmetry 2003, 14, 2021.

(305) Luche, J. L. Journal of the American Chemical Society 1978, 100, 2226.

(306) Gemal, A. L.; Luche, J. L. Journal of the American Chemical Society 1981, 103,

5454.

(307) Wutz, P. G. M.; Greene, T. W. Greene's Protective Groups in Organic

Synthesis; 4 ed.; Wile-Interscience, 2006.

(308) Mehta, G.; Pan, S. C. Tetrahedron Letters 2005, 46, 5219.

(309) Henton, D. R.; McCreery, R. A.; Swenton, J. S. The Journal of Organic

Chemistry 1980, 45, 369.

(310) Ohta, S.; Hayakawa, S.; Nishimura, K.; Okamoto, M. Tetrahedron Letters 1984,

25, 3251.

(311) Clark, J. H. Chemical Reviews 1980, 80, 429.

257

(312) Tojo, G.; Fernandez, M. I. Oxidation of Alcohols to Aldehydes and Ketones;

Springer, 2006.

(313) Tohma, H.; Kita, Y. Advanced Synthesis & Catalysis 2004, 346, 111.

(314) Duschek, A.; Kirsch, S. F. Angewandte Chemie International Edition 2011, 50,

1524.

(315) Frigerio, M.; Santagostino, M.; Sputore, S. The Journal of Organic Chemistry

1999, 64, 4537.

(316) More, J. D.; Finney, N. S. Organic Letters 2002, 4, 3001.

(317) Frigerio, M.; Santagostino, M. Tetrahedron Letters 1994, 35, 8019.

(318) Su, J. T.; Goddard, W. A. Journal of the American Chemical Society 2005, 127,

14146.

(319) Roth, G. J.; Liepold, B.; Müller, S. G.; Bestmann, H. J. Synthesis 2004, 2004,

59.

(320) Zanatta, S. D. Australian Journal of Chemistry 2007, 60, 963.

(321) Müller, S.; Liepold, B.; Roth, G. J.; Bestmann, H. J. Synlett 1996, 1996, 521.

(322) Pietruszka, J.; Witt, A. Synthesis 2006, 2006, 4266.

(323) Seyferth, D.; Marmor, R. S.; Hilbert, P. The Journal of Organic Chemistry 1971,

36, 1379.

(324) Gilbert, J. C.; Weerasooriya, U. The Journal of Organic Chemistry 1982, 47,

1837.

(325) Brown, D. G.; Velthuisen, E. J.; Commerford, J. R.; Brisbois, R. G. The Journal

of Organic Chemistry 1996, 61, 2540.

(326) Beard, C. D.; Craig, J. C. Journal of the American Chemical Society 1974, 96,

7950.

(327) Colvin, E. W.; Hamill, B. J. Journal of the Chemical Society, Chemical

Communications 1973, 0, 151.

(328) Miwa, K.; Aoyama, T.; Shioiri, T. Synlett 1994, 1994, 107.

(329) Colvin, E. W.; Hamill, B. J. Journal of the Chemical Society, Perkin


(330) Jafarzadeh, M. Synlett 2007, 2007, 2144.

(331) Michel, P.; Gennet, D.; Rassat, A. Tetrahedron Letters 1999, 40, 8575.

(332) Habrant, D.; Rauhala, V.; Koskinen, A. M. P. Chemical Society Reviews 2010,

39, 2007.

(333) Corey, E. J.; Fuchs, P. L. Tetrahedron Letters 1972, 13, 3769.

(334) Desai, N. B.; McKelvie, N.; Ramirez, F. Journal of the American Chemical

Society 1962, 84, 1745.

(335) Mori, M.; Tonogaki, K.; Kinoshita, A. Organic Syntheses 2005, 81.

(336) Grandjean, D.; Pale, P.; Chuche, J. Tetrahedron Letters 1994, 35, 3529.

(337) Mori, M.; Tonogaki, K.; Kinoshita, A. Organic Synthesis 2005, 81, 1.

(338) Tang, J.-S.; Tian, M.; Sheng, W.-B.; Guo, C.-C. Synthesis 2012, 2012, 541.

(339) Corey, E. J.; Venkateswarlu, A. Journal of the American Chemical Society 1972,

94, 6190.

(340) Jin, J.; Weinreb, S. M. Journal of the American Chemical Society 1997, 119,

5773.

(341) Hughes, A. B.; Sargent, M. V. J. Chem. Soc., Perkin Trans. 1 1989, 1787.

(342) Hughes, A. B.; Sargent, M. V. Journal of the Chemical Society, Perkin

Transactions 1 1989, 1787.

(343) Wang, Z.-X.; Tu, Y.; Frohn, M.; Zhang, J.-R.; Shi, Y. Journal of the American


(344) Frohn, M.; Shi, Y. Synthesis 2000, 2000, 1979.

(345) Tian, H.; She, X.; Shu, L.; Yu, H.; Shi, Y. Journal of the American Chemical

Society 2000, 122, 11551.

258

(346) Zhao, M.-X.; Shi, Y. The Journal of Organic Chemistry 2006, 71, 5377.

(347) Wang, Z.-X.; Cao, G.-A.; Shi, Y. The Journal of Organic Chemistry 1999, 64,

7646.

(348) Hookins, D. R.; Taylor, R. J. K. Tetrahedron Letters 2010, 51, 6619.

(349) Trost, B. M. Tetrahedron 1977, 33.

(350) Tsuji, J. Tetrahedron 1986, 42.

(351) Trost, B. M. Angewandte Chemie 1989, 28.

(352) Song, C.; Knight, D. W.; Whatton, M. A. Organic Letters 2005, 8, 163.

(353) Zonta, C.; Fabris, F.; De Lucchi, O. Organic Letters 2005, 7, 1003.

(354) Song, C.; Knight, D. W.; Whatton, M. A. Tetrahedron Letters 2004, 45, 9573.

(355) Watanabe, Y.; Laschat, S.; Budde, M.; Affolter, O.; Shimada, Y.; Urlacher, V.

B. Tetrahedron 2007, 63, 9413.

(356) Wang, X.; List, B. Angewandte Chemie International Edition 2008, 47, 1119.

(357) Wittig, G.; Schöllkopf, U. Chemische Berichte 1954, 87, 1318.

(358) Hoffmann, R. W. Angewandte Chemie International Edition 2001, 40, 1411.

(359) Clayden, J.; Warren, S.; Greeves, N. Organic Chemistry; 2 ed.; Oxford

University Press: Oxford, 2012.

(360) Reitz, A. B.; Nortey, S. O.; Jordan, A. D.; Mutter, M. S.; Maryanoff, B. E. The

Journal of Organic Chemistry 1986, 51, 3302.

(361) Schlosser, M.; Christmann, D. F. Liebigs Annalen Chemie 1967, 1, 708.

(362) Okazoe, T.; Takai, K.; Utimoto, K. Journal of the American Chemical Society

1987, 109, 951.

(363) Takai, K.; Nitta, K.; Utimoto, K. Journal of the American Chemical Society

1986, 108, 7408.

(364) Liu, P.; Jacobsen, E. N. Journal of the American Chemical Society 2001, 123,

10772.

(365) Zweifel, G.; Whitney, C. C. Journal of the American Chemical Society 1967, 89,

2753.

(366) Shakhmaev, R.; Ishbaeva, A.; Sunagatullina, A.; Zorin, V.; Springer Science &

Business Media B.V.: 2011; Vol. 81, p 1915.

(367) Grandjean, D.; Pale, P. Tetrahedron Letters 1993, 34, 1155.

(368) Mahler, H.; Braun, M. Chemische Berichte 1991, 124, 1379.

(369) Mahler, H.; Braun, M. Tetrahedron Letters 1987, 28, 5145.

(370) Rayner, C. M.; Astles, P. C.; Paquette, L. A. Journal of the American Chemical

Society 1992, 114, 3926.

(371) Stephens, R. D.; Castro, C. E. The Journal of Organic Chemistry 1963, 28,

3313.

(372) Waser, J.; Gaspar, B.; Nambu, H.; Carreira, E. M. Journal of the American


(373) Taniguchi, M.; Kobayashi, S.; Nakagawa, M.; Hino, T.; Kishi, Y. Tetrahedron

Letters 1986, 27, 4763.

(374) Brown, H. C.; Bhat, N. G.; Somayaji, V. Organometallics 1983, 2, 1311.

(375) Liu, X. Synlett 2003, 2003, 2442.

(376) Armarego, W. L. F.; Chai, C. L. L. Purification of laboratory chemicals;

Butterworth/Heinemann: Amsterdam, Boston, 2003.

(377) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. The Journal of Organic Chemistry

1997, 62, 7512.

(378) Zhou, Y.; Gao, G.; Li, H.; Qu, J. Tetrahedron Letters 2008, 49, 3260.

(379) Hossain, M. D.; Kitamura, T. The Journal of Organic Chemistry 2005, 70, 6984.

(380) Wenkert, E.; Loeser, E.-M.; Mahapatra, S. N.; Schenker, F.; Wilson, E. M. The

Journal of Organic Chemistry 1964, 29, 435.

259

(381) Klutchko, S.; Cohen, M. P.; Shavel, J.; Von Strandtmann, M. Journal of

Heterocyclic Chemistry 1974, 11, 183.

(382) Boeckman, R. K.; Shao, P.; Mullins, J. J. Organic Syntheses 2004, 10, 696.

(383) Davies, H. M. L.; William R. Cantrell, J.; Romines, K. R.; Baum, J. S. Organic

Syntheses 1998, 9.

(384) Kitamura, M.; Tashiro, N.; Miyagawa, S.; Okauchi, T. Synthesis 2011, 2011,

1037.

(385) Goundry, W. R. F.; Baldwin, J. E.; Lee, V. Tetrahedron 2003, 59, 1719.

(386) Pirali, T.; Gatti, S.; Di Brisco, R.; Tacchi, S.; Zaninetti, R.; Brunelli, E.;

Massarotti, A.; Sorba, G.; Canonico, P. L.; Moro, L.; Genazzani, A. A.; Tron, G.

C.; Billington, R. A. ChemMedChem 2007, 2, 437.

(387) Henton, D. R.; Chenard, B. L.; Swenton, J. S. Journal of the Chemical Society,

Chemical Communications 1979, 0, 326.

(388) Lei, X.; Johnson, R. P.; Porco, J. A. Angewandte Chemie International Edition

2003, 42, 3913.

(389) Hughes, A. B.; Sargent, M. V. Journal of the Chemical Society, Perkin


(390) Fang, Y.; Leysen, D.; Ottenheijm, H. C. J. Synthetic Communications 1995, 25,

1857.

(391) Harrington, P. J.; Sanchez, I. H. Synthetic Communications 1994, 24, 175.

(392) Elgendy, E. M.; Khayyat, S. A. Russian Journal of Organic Chemistry 2008, 44,

814.

(393) Cicala, G.; Curci, R.; Fiorentino, M.; Laricchiuta, O. The Journal of Organic

Chemistry 1982, 47, 2670.

(394) Sheldrick, G. M. Acta Crystal 2008, A64.

260

261

Chapter 7

Appendix

262

263

7.1 Crystal structures

7.1.1 General Information

Crystallographic data for all structures were collected by Dr. B. W. Skelton at 100(2) K

on an Oxford Diffraction Xcalibur diffractometer fitted with Mo Kα radiation

(λ = 0.71073 Å). Following analytical absorption corrections and solution by direct

methods, the structures were refined against F2 with full-matrix least-squares using the

program SHELXL-97.394

All hydrogen atoms were added at calculated positions and

refined by use of a riding model with isotropic displacement parameters based on those

of the parent atom. Anisotropic displacement parameters were employed for the non-

hydrogen atoms.

Crystallographic data and figures showing ORTEP representations of individual

molecules for the crystal structures described in this thesis are presented. ORTEP of

ellipsoids have been drawn at the 50% probability level for the non-hydrogen atoms.

Hydrogen atoms, where shown, have arbitrary radii of 0.1 Å. Tables of bond lengths

and angles for the crystal structures described in this thesis are also presented.

7.1.2 6-(Bromoethynyl)-5,5-dimethoxy-7-oxabicyclo[4.1.0]hept-3-en-2-one (275)

Crystals of 275 suitable for X-ray studies were grown from the slow evaporation of

hexane solutions.

Empirical formula C10H9BrO4

Formula weight 273.08

Temperature 100(2) K

Wavelength 0.71073 Å

Crystal system Monoclinic

264

Space group P21

Unit cell dimensions a = 6.8771(7) Å

b = 6.7430(6) Å

c = 11.0482(12) Å

β = 95.269(9)°

Volume 510.17(9) Å3

Z 2

Density (calculated) 1.778 Mg/m3

Absorption coefficient 4.019 mm-1

F(000) 272

Crystal size 0.27 x 0.10 x 0.05 mm3

θ range for data collection 2.97 to 36.22°

Index ranges -11<=h<=11, -11<=k<=11, -18<=l<=18

Reflections collected 15017

Independent reflections 4663 [R(int) = 0.0743]

Completeness to θ = 35.50° 99.6 %

Absorption correction Analytical

Max. and min. transmission 0.864 and 0.496

Refinement method Full-matrix least-squares on F2

Data / restraints / parameters 4663 / 1 / 138

Goodness-of-fit on F2 1.112

Final R indices [I>2σ(I)] R1 = 0.0689, wR2 = 0.1295

R indices (all data) R1 = 0.0905, wR2 = 0.1413

Absolute structure parameter 0.016(14)

Largest diff. peak and hole 2.300 and -0.676 e.Å-3

265

Figure 3.08. A single X-ray crystal structure ORTEP (50% probability) of bromo-alkyne 275.

Bond lengths (Å):

C(1)-O(7) 1.441(5)

C(1)-C(6) 1.491(6)

C(1)-C(2) 1.498(6)

C(2)-O(2) 1.221(5)

C(2)-C(3) 1.467(5)

C(3)-C(4) 1.335(6)

C(4)-C(5) 1.511(6)

C(5)-O(51) 1.416(5)

C(5)-O(52) 1.424(5)

C(5)-C(6) 1.530(5)

O(51)-C(51) 1.434(5)

O(52)-C(52) 1.433(5)

C(6)-O(7) 1.428(5)

C(6)-C(61) 1.446(6)

C(61)-C(62) 1.193(6)

C(62)-Br(1) 1.803(4)

266

Bond angles (°):

O(7)-C(1)-C(6) 58.3(2)

O(7)-C(1)-C(2) 117.7(3)

C(6)-C(1)-C(2) 119.9(4)

O(2)-C(2)-C(3) 123.5(4)

O(2)-C(2)-C(1) 120.6(4)

C(3)-C(2)-C(1) 115.9(3)

C(4)-C(3)-C(2) 121.5(4)

C(3)-C(4)-C(5) 125.3(4)

O(51)-C(5)-O(52) 111.9(3)

O(51)-C(5)-C(4) 102.0(3)

O(52)-C(5)-C(4) 113.8(3)

O(51)-C(5)-C(6) 112.3(3)

O(52)-C(5)-C(6) 103.7(3)

C(4)-C(5)-C(6) 113.3(3)

C(5)-O(51)-C(51) 118.2(3)

C(5)-O(52)-C(52) 114.1(3)

O(7)-C(6)-C(61) 116.2(3)

O(7)-C(6)-C(1) 59.1(2)

C(61)-C(6)-C(1) 116.8(3)

O(7)-C(6)-C(5) 112.8(3)

C(61)-C(6)-C(5) 118.9(3)

C(1)-C(6)-C(5) 118.6(3)

C(62)-C(61)-C(6) 176.9(4)

C(61)-C(62)-Br(1) 179.7(4)

C(6)-O(7)-C(1) 62.6(2)

267

7.1.3 (2Z)-3-iodo-1-[1-[(4-methylphenyl)sulfonyl]-1H-pyrrol-2-yl]but-2-en-1-one

(327)

Crystals of 327 suitable for X-ray studies were grown from the slow evaporation of

CH2Cl2/hexane solutions.

Empirical formula C15H14INO3S

Formula weight 415.23

Temperature 100(2) K

Wavelength 0.71073 Å

Crystal system Monoclinic

Space group P 1 2/c 1

Unit cell dimensions a = 10.2398(5) Å α = 90°.

b = 21.2574(8) Å β = 104.026(6)°.

c = 7.3901(5) Å γ = 90°.

Volume 1560.65(14) Å3

Z 4

Density (calculated) 1.767 Mg/m3

Absorption coefficient 2.194 mm-1

F(000) 816

Crystal size 0.68 x 0.11 x 0.05 mm3

Theta range for data collection 3.53 to 31.00°

Index ranges -14<=h<=14, -30<=k<=30, -10<=l<=10

Reflections collected 30192

Independent reflections 4964 [R(int) = 0.0766]

Completeness to theta = 31.00° 99.8 %

Absorption correction Analytical

Max. and min. transmission 0.918 and 0.523

Refinement method Full-matrix least-squares on F2

268

Data / restraints / parameters 4964 / 2 / 200

Goodness-of-fit on F2

1.263

Final R indices [I>2sigma(I)] R1 = 0.0680, wR2 = 0.1356

R indices (all data) R1 = 0.0750, wR2 = 0.1384

Largest diff. peak and hole 1.224 and -1.631 e.Å-3

Figure 4.03. A single X-ray crystal structure ORTEP (50% probability) of 327.

Bond lengths (Å):

N(1)-C(5) 1.385(5)

N(1)-C(2) 1.411(5)

N(1)-S(1) 1.695(3)

S(1)-O(11) 1.430(3)

S(1)-O(12) 1.434(3)

S(1)-C(11) 1.749(4)

C(11)-C(16) 1.383(6)

C(11)-C(12) 1.392(6)

C(12)-C(13) 1.378(6)

C(12)-H(12) 0.9500

C(13)-C(14) 1.396(6)

269

C(13)-H(13) 0.9500

C(14)-C(15) 1.386(6)

C(14)-C(17) 1.505(6)

C(15)-C(16) 1.390(6)

C(15)-H(15) 0.9500

C(16)-H(16) 0.9500

C(17)-H(17A) 0.9800

C(17)-H(17B) 0.9800

C(17)-H(17C) 0.9800

C(2)-C(3) 1.381(5)

C(2)-C(21) 1.458(6)

C(21)-O(21) 1.223(5)

C(21)-C(22) 1.483(5)

C(22)-C(23) 1.316(6)

C(22)-H(22) 0.9500

C(23)-C(24') 1.520(12)

C(23)-C(24) 1.551(9)

C(23)-I(2) 2.073(4)

C(24)-H(24A) 0.9800

C(24)-H(24B) 0.9800

C(24)-H(24C) 0.9800

C(24')-H(24D) 0.9800

C(24')-H(24E) 0.9800

C(24')-H(24F) 0.9800

C(3)-C(4) 1.421(6)

C(3)-H(3) 0.9500

C(4)-C(5) 1.376(6)

C(4)-H(4) 0.9500

C(5)-H(5) 0.9500

Bond angles (°):

C(5)-N(1)-C(2) 108.4(3)

C(5)-N(1)-S(1) 120.5(3)

C(2)-N(1)-S(1) 130.7(3)

O(11)-S(1)-O(12) 119.33(19)

270

O(11)-S(1)-N(1) 108.85(17)

O(12)-S(1)-N(1) 103.19(18)

O(11)-S(1)-C(11) 111.37(19)

O(12)-S(1)-C(11) 107.5(2)

N(1)-S(1)-C(11) 105.49(18)

C(16)-C(11)-C(12) 120.8(4)

C(16)-C(11)-S(1) 121.8(3)

C(12)-C(11)-S(1) 117.3(3)

C(13)-C(12)-C(11) 119.5(4)

C(13)-C(12)-H(12) 120.3

C(11)-C(12)-H(12) 120.3

C(12)-C(13)-C(14) 120.7(4)

C(12)-C(13)-H(13) 119.6

C(14)-C(13)-H(13) 119.6

C(15)-C(14)-C(13) 118.8(4)

C(15)-C(14)-C(17) 121.4(4)

C(13)-C(14)-C(17) 119.7(4)

C(14)-C(15)-C(16) 121.1(4)

C(14)-C(15)-H(15) 119.4

C(16)-C(15)-H(15) 119.4

C(11)-C(16)-C(15) 119.0(4)

C(11)-C(16)-H(16) 120.5

C(15)-C(16)-H(16) 120.5

C(14)-C(17)-H(17A) 109.5

C(14)-C(17)-H(17B) 109.5

H(17A)-C(17)-H(17B) 109.5

C(14)-C(17)-H(17C) 109.5

H(17A)-C(17)-H(17C) 109.5

H(17B)-C(17)-H(17C) 109.5

C(3)-C(2)-N(1) 106.7(3)

C(3)-C(2)-C(21) 129.1(3)

N(1)-C(2)-C(21) 123.6(3)

O(21)-C(21)-C(2) 122.0(4)

O(21)-C(21)-C(22) 122.9(4)

C(2)-C(21)-C(22) 115.0(3)

271

C(23)-C(22)-C(21) 127.9(4)

C(23)-C(22)-H(22) 116.0

C(21)-C(22)-H(22) 116.0

C(22)-C(23)-C(24') 124.8(8)

C(22)-C(23)-C(24) 118.9(5)

C(24')-C(23)-C(24) 116.0(8)

C(22)-C(23)-I(2) 124.5(3)

C(24')-C(23)-I(2) 110.6(7)

C(24)-C(23)-I(2) 7.6(3)

C(23)-C(24)-H(24A) 109.5

C(23)-C(24)-H(24B) 109.5

C(23)-C(24)-H(24C) 109.5

C(23)-C(24')-H(24D) 109.5

C(23)-C(24')-H(24E) 109.5

H(24D)-C(24')-H(24E) 109.5

C(23)-C(24')-H(24F) 109.5

H(24D)-C(24')-H(24F) 109.5

H(24E)-C(24')-H(24F) 109.5

C(2)-C(3)-C(4) 109.0(4)

C(2)-C(3)-H(3) 125.5

C(4)-C(3)-H(3) 125.5

C(5)-C(4)-C(3) 106.8(4)

C(5)-C(4)-H(4) 126.6

C(3)-C(4)-H(4) 126.6

C(4)-C(5)-N(1) 109.1(4)

C(4)-C(5)-H(5) 125.4

N(1)-C(5)-H(5) 125.4

Studies into the Total Syntheses of Various Natural ... · various natural products and their derivatives for biological evaluation. ... using the Negishi and Suzuki cross-coupling

Documents