Biomedical Engineering Reference
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Me
O
N
H
CN
CN
Me
Me
Me
Me
Me
114
(30 mol%)
Cu(OTf)
2
, TFA
NaTFA
Me
Me
CN
CN
H
H
i
-PrCN, DME, rt, 24 h
56%
H
O
H
O
H
113
115
(ee = 92%)
SCHEME 6.23
Enantioselective SOMO cyclization of polyunsaturated aldehyde.
6.3. HETEROATOM INSTALLATION
6.3.1. Epoxidation of Alkene
The enantioselective epoxidation of alkenes is one of the most important transforma-
tions in organic synthesis. Although the Katsuki-Sharpless epoxidation is well
established for allylic alcohols [42], its application to nonfuctionalized alkene is
found to be difficult.
Shi and coworkers developed an efficient asymmetric epoxidation catalyzed by
a fructose-derived ketone
116
, which affords chiral epoxides such as
117
and
118
in
good to high yields and in almost enantiomerically pure form (Scheme 6.24) [43].
Armstrong et al. reported an asymmetric epoxidation catalyzed by 2-fluoro-
N
-
carbethoxytropinone (
119
) [44].
O
R
1
R
1
organocatalysis
R
3
R
3
Oxone
®
R
2
R
2
Me
Me
O
Ph
Catalyst:
Product:
Ph
O
O
O
117
(78%, ee = 99%)
Ph
O
O
O
O
116
Me
Me
118
(94%, ee = 98%)
CO
2
Et
N
F
O
Ph
Ph
H
Ph
O
120
(100%, ee = 83%)
119
SCHEME 6.24
Organocatalytic epoxidation of alkenes.
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