Page 596 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

5.21. Solvohalogenation can be used to achieve both regio- and stereochemical control 577
for synthetic purposes in alkene addition reactions. Some examples are shown
below. Discuss the factors that lead to the observed regio- or stereochemical PROBLEMS
outcome.

a. Control of the stereochemistry of an epoxide:

Br
CH 3 H C CH 3 O
3
NBS OH NaOH
O H O O EtOH O
2
H H
CH 3 O H
direct
epoxidation
O
H
b. Formation of cis-diols:

CH 3 CH 3
CHCO CH 3 HO
NBS Ph 2 2 Br 1) KOtBu OH
Ph CHCO H 2)K CO
2
2
2
3
CH 3 CH
CH 3 CH 3 3 CH
CH 3 3
c. Chemoselective functionalization of polyalkenes:
CH OCH 3 CH 2 OCH 3
2
NBS Br
t-BuOH, H O
2
OH