Download 08/31/2007

Princeton University Mechanisms Club
Friday, August 31, 2007
Grace Wang, moderator
Themes: Three-Dimensional Drawings and OOMFCPOAT1
Question 1
A) Provide a mechanism for the formation of G from the 1:1 mixture of alcohols.
TsO
iPrMgCl
!
OH
Me
O
O
Me
Me
+
H
1:1 mixture of alcohols
H
H
G
only observed product
W
B) Rationalize why W is not observed.
Question 2
In a paper by Woerpel and coworkers (JOC, 1997, 62, 5674-5), tandem aldol!Tischenko
reactions are used to diastereoselectively synthesize diols and triols. Rationalize the
diastereoselectivity of the reaction below.
O
1.2 equiv LDA
2.0 equiv MeCHO
O
Ph
Et
!78 °C to !22 °C
OH
O
Me
Me
Ph
Me
1
One Of My Favorite Chemistry Professors Of All Time.
98% ds
Question 3
Woerpel and coworkers (JOC, 2002, 67, 2056-64) have extensively examined diastereoselective
nucleophilic substitution reactions of oxasilacyclopentane acetals. Rationalize the observed selectivities.
A) 2,3-cis Me vs. 2,3-trans Me
t-Bu
t-Bu Si O
t-Bu
t-Bu Si O
OAc
Me
Me
TMS
Me
t-Bu
t-Bu Si O
t-Bu
t-Bu Si O
OAc
Me
98% ds
Me
SnBr4
Me
TMS
Me
SnBr4
57% ds
Me
B) Different nucleophiles
t-Bu
t-Bu Si O
t-Bu
t-Bu Si O
OAc
Me
98% ds
SnBr4
OTMs
t-Bu
t-Bu Si O
Et
OAc
Me
TMS
Me
t-Bu
t-Bu Si O
O
Me
SnBr4
Et
Me
Me
92% ds