Chapter 7 Alkenes and Alkynes I: Properties and Synthesis ...
123.202 Lecture 7 - alkenes
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Transcript of 123.202 Lecture 7 - alkenes
©mugley@flickralkenes LECTURE SEVEN
➊hydrogenationof alkenes
H2Pd/C H
H
synaddition
©Oberazzi@flickr
H H H H HH
reactionsurface
H H H H HH
reactionsurface
H H H H HH
reactionsurface
delivered fromH
same face
©e-magic@flickr
of stereochemistryimportance
H2Pd/C
H2Pd/C ??
of stereochemistryimportance
H2Pd/C
H H
Z-alkenecis
mesoachiral
of stereochemistryimportance
H2Pd/C
H H
E-alkenetrans
chiral
©VT Jenny@Horticulture in the desert
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
©wonderferret@flickr
©Grant and Caroline@flickr
poisoningcatalyst
Pd/CaCO3/Pb
reductionpartial E-alkene
trans
antiaddition
NaNH3(l) H
H
©carbonNYC@flickr
©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
©Aidan O'Sullivan@flickr
remember
attack δ+ or +electrons