123.202 Lecture 7 - alkenes

©mugley@flickralkenes LECTURE SEVEN

➊hydrogenationof alkenes

H2Pd/C H

H

synaddition

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H H H H HH

reactionsurface

H H H H HH

reactionsurface

H H H H HH

reactionsurface

delivered fromH

same face

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of stereochemistryimportance

H2Pd/C

H2Pd/C ??

of stereochemistryimportance

H2Pd/C

H H

Z-alkenecis

mesoachiral

of stereochemistryimportance

H2Pd/C

H H

E-alkenetrans

chiral

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example

O

O

OO OMe

OHOO

OH

H

resiniferatoxin

example

O

O

OO OMe

OHOO

OH

H

resiniferatoxin

1000x

O

O

OO OMe

OHOO

OH

H

resiniferatoxin

example

J. Am. Chem. Soc., 1997, 119, 12976

OAc

OBn

OTBS

HO

O

OAc

OBn

OTBS

HO

O

H210% Pd/C

99%

HH

HH

H H

➋hydrogenationof alkynes

reductionfull

H2Pd/C

HH

HH

reductionpartial

H2Lindlar catalyst H H

Z-alkenecis

synaddition

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poisoningcatalyst

Pd/CaCO3/Pb

reductionpartial E-alkene

trans

antiaddition

NaNH3(l) H

H

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©P.P.Edwards@Oxford University

Na NH3 Na e [NH3]n

eH NH2

HeH

H NH2

H

H

mechanism

radical

isomerisationpermits

O OH O

O

HO N

S

epothilone C

example

O OTBS O

O

TBSO N

S

i. H2, Lindlar cat.ii. HF(79%)

O OH O

O

HO N

S

HH

hydration

& acid-catalysed➌hydrohalogenation

H XX

H

H X H Xstep 1

step 2

HX

mechanism

nucleophileelectrophile

H O Hstep 1

step 2

HO

H

HO

H

H

H H

mechanism

nucleophileelectrophile

H O Hstep 1

step 2

HO

H

HO

H

H

H H

HO

H HO

H

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remember

attack δ+ or +electrons