Download - 123.202 Lecture 7 - alkenes
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©mugley@flickralkenes LECTURE SEVEN
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➊hydrogenationof alkenes
H2Pd/C H
H
synaddition
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H H H H HH
reactionsurface
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H H H H HH
reactionsurface
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H H H H HH
reactionsurface
delivered fromH
same face
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of stereochemistryimportance
H2Pd/C
H2Pd/C ??
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of stereochemistryimportance
H2Pd/C
H H
Z-alkenecis
mesoachiral
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of stereochemistryimportance
H2Pd/C
H H
E-alkenetrans
chiral
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©VT Jenny@Horticulture in the desert
example
O
O
OO OMe
OHOO
OH
H
resiniferatoxin
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example
O
O
OO OMe
OHOO
OH
H
resiniferatoxin
1000x
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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
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➋hydrogenationof alkynes
reductionfull
H2Pd/C
HH
HH
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reductionpartial
H2Lindlar catalyst H H
Z-alkenecis
synaddition
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poisoningcatalyst
Pd/CaCO3/Pb
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reductionpartial E-alkene
trans
antiaddition
NaNH3(l) H
H
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©P.P.Edwards@Oxford University
Na NH3 Na e [NH3]n
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eH NH2
HeH
H NH2
H
H
mechanism
radical
isomerisationpermits
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O OH O
O
HO N
S
epothilone C
example
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O OTBS O
O
TBSO N
S
i. H2, Lindlar cat.ii. HF(79%)
O OH O
O
HO N
S
HH
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hydration
& acid-catalysed➌hydrohalogenation
H XX
H
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H X H Xstep 1
step 2
HX
mechanism
nucleophileelectrophile
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H O Hstep 1
step 2
HO
H
HO
H
H
H H
mechanism
nucleophileelectrophile
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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