Rhenium-Catalyzed Didehydroxylation of Vicinal Diols to Alkenes Using a Simple Alcohol as a Reducing Agent Elena Arceo, Jonathan A. Ellman, Robert G. Bergman J. Am. Chem. Soc. 2010, 132, ASAP On the Absolute Configurational Stability of Bromonium and Chloronium Ions Scott E. Denmark, Matthew T. Burk, Andrew J. Hoover J. Am. Chem. Soc. 2010, 132, 1232-1233 Antoinette Nibbs Short Literature Presentation 23 August 2010 R OH OH R R R R R R R X
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Rhenium-Catalyzed Didehydroxylation of Vicinal Diols to Alkenes Using a Simple Alcohol as a Reducing Agent
Elena Arceo, Jonathan A. Ellman, Robert G. BergmanJ. Am. Chem. Soc. 2010, 132, ASAP
On the Absolute Configurational Stability of Bromonium and Chloronium Ions
Scott E. Denmark, Matthew T. Burk, Andrew J. HooverJ. Am. Chem. Soc. 2010, 132, 1232-1233
Antoinette NibbsShort Literature Presentation
23 August 2010
R
OH
OH
RR
R
RR R
RX
development of new methods for production of reduced oxygen-content from renewable biomass resources
development of new methods for production of reduced oxygen-content from renewable biomass resources
Deoxygenation of Biomass Polyols
Arceo, E; Marsden, P.; Bergman, R. G.; Ellman, J. A. Chem. Commun. 2009, 3357
development of new methods for production of reduced oxygen-content from renewable biomass resources
sustainable production of transportation fuels from biomass in an integrated biomass production-conversion system
Huber, G. W.; Iborra, S.; Corma, A. Chem. Rev. 2006, 106, 4044-4098
single-flask, solvent-free deoxygenation procedure to convert glycerol into allyl alcohol (polymer, 3-hydroxyproionic acid)
Prior Art
OH
OH
OO
OO
MeMe
MeMe
Cp*ReO3, PPh3
C6H5Cl, 125 °C, 80h
OO
OO
MeMe
MeMe
86% bdc
Cook, G. C. and Andrews, M. A. J. Am. Chem. Soc. 1996, 118, 9448-9449
O
R'
OH
R'R
HOor
MeReO3 (5-10 mol %)
H2 (80-300 psi), 150 °C, THF R'R18-96% yield
Ziegler, J. E.; Zdilla, M. J.; Evans, A. J.; Abu-Omar, M. M. Inorg. Chem. 2009, 48, 9998-10000
reaction did not proceed in the presence of acid and absence of catalyst
Applications
(62% NMR yield)55% isolated yield>94 mol % pure
meso-erythritol
HOOH
OHOH
Re2(CO)10 (1.5 mol %)
TsOH (1.7 mol %)160 °C, 12 h3-octanol, air
O
O
HO OH
Huber, G. W.; Iborra, S.; Corma, A. Chem. Rev. 2006, 106, 4044-4098
Reaction Mechanism
"In contrast to the simplicity of the reaction methodology, the mechanism of the reaction is still unknown."
temperature and oxygen dependence suggests an oxidized rhenium species as the active catalystand...
diol has to be capable of achieving cis stereochemistryso...
rhenium diolate species
some metal diolates extrude corresponding alkene on thermolysis
affect of acid on catalyst related to assisted olefin extrusion by protonation of a rhenium diolate intermediate
Conclusions
method can be applied to producing unsaturated compounds from other biomass-derived polyols
new catalytic system rhenium-mediated didehydroxylation of vicinal diols (internal or external) using external alcohol as an environmentally friendly reducing agent
(62% NMR yield)55% isolated yield>94 mol % pure
meso-erythritol
HOOH
OHOH
Re2(CO)10 (1.5 mol %)
TsOH (1.7 mol %)160 °C, 12 h3-octanol, air
O
addition of acid allows for milder reaction conditions (155 °C, up to 2 h reaction time)
OH
(3R*,4R*)-decane-3,4-diol
Re2(CO)10 (2.5 mol %)
3-octanol, 170 °C, air2 h
(82%)
MeOH
(CH2)4CH3 (CH2)4CH3Me
only a few enantioselective variants
few of those variants require substoichiometric amounts of chiral promoter
Electrophilic Halofunctionalization of Olefins
Kwon, H.; Park, C.; Lee, S.; Youn, J.; Kang, S. Chem. Eur. J. 2008, 14, 1023-1028
Snyder, S. A.; Tang, Z.-Y.; Gupta, R. J. Am. Chem. Soc. 2009, 131, 5744-5745
OHOH
swainsonine
OH
N3
NCS, I2, K2CO3, cat.
PhMe, —78 °C
86%, 90% ee
N
OH OH
OH
HO
IN3
O
N
t-Bu
t-Bu
N
O t-Bu
t-Bu
CrCl
O
O
OH
MOMO O MeMe
BH3·THF, cat.
Cl2, THF, —78 °C
O
O
OH
MOMO O MeMe
ClCl
93%, 87% ee
O
O
OMe
MOMO O
Cl
Me
Me
Me
MeMe
Cl
(—)-napyradiomycin A1
Electrophilic Halofunctionalization of Olefins
Snyder, S. A.; Tang, Z.-Y.; Gupta, R. J. Am. Chem. Soc. 2009, 131, 5744-5745
O
O
OMe
MOMO O
Cl
Me
Me
Me
MeMe
Cl
(—)-napyradiomycin A1
Me
Cl
Cl
OSO3H
Cl
Cl
Cl
Cl
chlorosulpholipid cytotoxin
Nilewski, C.; Geisser, R. W.; Carreira, E. M., Nature 2009, 457, 573-576Bedke, D. K.; Sibuya, G. M.; Pereira, A.; Gerwick, W. H.; Haines, T. H.; Vanderwal, C. D. J. Am. Chem. Soc. 2009, 131, 7570-7572
only a few enantioselective variants
few of those variants require substoichiometric amounts of chiral promoter
bromine exchange between bromonium ions and olefins can be rapid
Neverov, A. A.; Brown, R. S. J. Org. Chem. 1996, 61, 962-968
The paucity of such methods can be ascribed in part to a lack of understanding of the factors that influence the configurational stability of the intermediate halonium ions.
What Do We Know About Them?
Denmark, S. E.; Collins, W. R.; Cullen, M. D. J. Am. Chem. Soc. 2009, 131, 3490-3492
E
R1
H
R1
R SbF6
R2
R2 CD2Cl2
temp R1
R1
E
R2
H
R2
R SbF6
RE = PhSe, n-BuSe
similar to processes for thiiranium and seleniranium ions
enantiopure bromonium ions have been demonstrated to be stable in the absence of olefins
no studies for olefin-to-olefin transfer observation
SO
OO
C10H21
Br
O
OO
OMe
TiCl4
enantiopure
C10H21
BrC10H21
ClBr
enantiopure product
Braddock, D. C.; Hermitage, S. A.; Kwok, L.; Pouwer, R.; Redmond, J. M.; White, A. J. P. Chem. Commun. 2009, 1082-1084
Absolute Configurational Stability of Bromonium Ions
RBr
RRR
RBr
R
establish configurational stability of bromonium and chloronium ions under conditions where racemization could be competitive with intermolecular trapping by nucleophiles
absolute configurational stability of chloronium ions has never been demonstrated under any conditionsrelative configurational stability established in classic studies by Lucas and Winstein
Lucas, H. J.; Gould, C. W., Jr. J. Am. Chem. Soc. 1941, 63, 2541-2551
Winstein, S.; Seymour, D. J. Am. Chem. Soc. 1946, 68, 119-122
Chloronium Ions In Days of Old
generated by anchimerically assisted ionization of enantiomerically enriched, C2 symmetric B-halo sulfonates in strongly ionizing media
• demonstrate bromonium ion formation and trapping in the presence of subsolvent quantities of nucleophiles• provide for degenerate bromine exchange• HFIP as solvent
n-Prn-Pr
OTs
Br
er = 97:3
HCO2Na (13 equiv)
HCO2H, 23 °C(68%)
n-Prn-Pr
OCHO
Br
er: 97:3 100% enantiospecificity
HCO2Na, HCO2H, 23 °C(82%)
(10 equiv)OBnBnO
establish configurational stability of bromonium and chloronium ions under conditions where racemization could be competitive with intermolecular trapping by nucleophiles
enantiospecificity = eeprod / eesm X 100%
Preliminary Experiments
whatʼs the next step?
HFIP strong ionizing solvent, low nucleophilicity
dissolve both nucleophilic salts and significant quantities of the olefin
minor racemization pathway - nucleophilic attack at bromine to generate BrN3
n-Prn-Pr
OTs
Br HFIP, 23 °C n-Prn-Pr
R
Br
Nu
n-Prn-Pr
OAc
Br
NaOAc (2 equiv)79% yield
97:3 er100% es
MeOH (10 equiv) n-Prn-Pr
OMe
Br
80% yield97:3 er
100% es
n-Prn-Pr
N3
Br
n-Bu4NN3 (2 equiv)80% yield
95:5 er96% es
Solvolysis of Enantiomerically Enriched Bromide
n-Prn-Pr
OTs
Br
MOAc
HFIP, 23 °Cn-Pr
n-PrOAc
Brn-Pr
n-Pr
Solvolysis of Enantiomerically Enriched Bromide
introduction of olefin leads to lower specificity
n-Prn-Pr
OTs
Br
MOAc
HFIP, 23 °Cn-Pr
n-PrOAc
Brn-Pr
n-Pr
increased trapping rate due to less coordinated and more nucleophillic anion
Solvolysis of Enantiomerically Enriched Bromide
introduction of olefin leads to lower specificity
assuming you can generate and trap chloronium ions enantiospecifically, even in the absence of olefin-to-olefin transfer
Denmark, S. E.; Collins, W. R.; Cullen, M. D. J. Am. Chem. Soc. 2009, 131, 3490-3492
E
R1
H
R1
R SbF6
R2
R2 CD2Cl2
temp R1
R1
E
R2
H
R2
R SbF6
RE = PhSe, n-BuSe
Modulating Olefin-to-Olefin Transfer Rate
HCO2Na, HCO2H, 23 °C(63%)
(10 equiv)OBnBnO
Solvolysis of Enantiomerically Enriched Chloride
n-Prn-Pr
OTf
Cl
er = 98:2dr > 99:1
HCO2Na (13 equiv)
HCO2H, 23 °C(76%)
n-Prn-Pr
OCHO
Cl
er = 98:2dr = 98:2
100% enantiospecificity
n-Prn-Pr
OTf
Cl
dr = 99:1
HCO2Na (13 equiv)
HCO2H, 23 °C(58%)
n-Prn-Pr
OCHO
Cl
dr = 97:3
NaOAc gave complex mixtures of products
low chemical stability of 1,2-dialkylchloronium ions dictates the use of more reactive nucleophile to trap them before low energy decomposition pathways can intervene
n-Prn-Pr
OTf
Cl HFIP/CH2Cl2 1:1, 23 °Cn-Pr
n-PrOR
Cl
Nu
n-Prn-Pr
R Nu olefin (equiv) yield (%) er e.s. (%)AcAcAcMe
n-Bu4NOAc n-Bu4NOAc n-Bu4NOAc MeOH
00.251.00
32394342
98:2 98:2 98:2 98:2
100100100100
Solvolysis of Enantiomerically Enriched Chloride
•lesser electronegativity of bromine•olefin-olefin transfer proceeds via nucleophilic attack by olefin at bromine•favored by greater positive charge on bromine
chemical stability stereochemical stability
inverse relationship
degree to which positive charge is located on the halogens in the halonium ion
n-Prn-Pr
Cl n-Prn-Pr
Br
•greater electronegativity of chlorine •less positive charge on chlorine•more positive charge on carbon•increased propensity toward processes characteristic of carbocations
Stability of Halonium Ions
demonstrated first enantioselective generation and trapping of chloronium ions
enantiospecific generation and trapping of bromonium ions
racemization of bromonium ions via olefin-to-olefin tranfer is competive with intermolecular capture by anionic nucleophiles
relative rates do not exclude possibility of a catalytic, enantioselective bromination process, but present an obstacle that must be surmounted by any successful catalyst system