Chemistry Reference
In-Depth Information
23
(2 mol
%)
O
R
+ 35% H
2
O
2
R
Ph
Ph
P
OH
2
CF
3
SO
-
58-98%
ee
Pt
+
F
P
F
F
Ph
Ph
F
F
O
23
O
O
O
O
O
98%, 58% ee
48%, 83% ee
63%, 78% ee
64%, 87% ee
Scheme 11.27.
23
(2 mol
%)
O
+ 35% H
2
O
2
66%, 98% ee
23
(2 mol
%)
O
+ 35% H
2
O
2
93%, 63% ee
O
23
(2 mol
%)
+ 35% H
2
O
2
96%, 86% ee
Scheme 11.28.
epoxidation of aliphatic olefi ns with aqueous hydrogen peroxide (Scheme 11.27) [42].
Various terminal olefi ns with no substituent at the allylic position are effi ciently con-
verted to the corresponding epoxides with moderate to high enantioselectivity. It is
worth noting that only one equivalent of 35% hydrogen peroxide is required to obtain
an acceptable yield. Another advantage is the high regio- and chemoselectivities. Mono-
substituted terminal olefi ns are selectively oxidized in the presence of internal or gemi-
nally disubstituted terminal olefi ns (Scheme 11.28). Although halogenated solvents
are commonly used, the reaction is also performed in water in the presence of
surfactants [43] .
The researchers proposed that H
2
O
2
binds to the
meta -
and
para -
fl uorine atoms
of the C
6
F
5
ligand by hydrogen bonding and that the olefi n coordinates to the plati-
num prior to the oxygen atom transfer [44]. Scheme 11.29 accounts for the limited
substrate scope and the extraordinary regioselectivity observed in the epoxidation of
dienes.
