Chemistry Reference
In-Depth Information
O
O
O
O
55
(1 mol %),
t
BuCHO
O
2
Ph
Ph
O
N
O
NO
2
+
Cu
Ph
O
2
N
O
N
O
47%, 69% ee
55
Scheme 11.65.
Me
2
AlCl (50 mol
%)
(
S
)-BINOL (50 mol
%)
Toluene
O
O
+ CHP
(1.5 equiv.)
O
R
R
58-73% ee
O
Me
2
AlCl (50 mol
%)
(
S
)-BINOL (50 mol
%)
Toluene
O
O
O
O
+ CHP
(1.5 equiv.)
+
34% ee
96% ee
Scheme 11.66.
O
R
3
O
M
R
2
R
1
O
Figure 11.7.
furnished the two lactones [120]. One is the lactone normally obtained in common
Baeyer-Villiger reactions, and the enantiomeric excess is as high as 34%. The other is
the constitutional isomer of the normal one and obtained with high enantioselectivity
of 96% ee. The subsequent studies employing substituted BINOL derivatives provided
a more effi cient method that needs less catalyst, and the high ee value of up to 84% ee
was achieved in the reaction of 3-phenylcyclobutanone [121]. The aluminum/BINOL
system was proposed to proceed via a cyclic Criegee intermediate involving a pentaco-
ordinated aluminum complex (Fig. 11.7 ).
The conformational regulation of metal-bound Criegee intermediates by chelate
formation was fi rst proven as an effi cient strategy by Uchida and Katsuki (Scheme 11.67)
[122]. They reported that chiral
cis
-
cobalt
III
complex
56
bearing axially chiral binaph-
thyldiamine catalyzes the Baeyer-Villiger oxidation of 3-substituted cyclobutanones in
the presence of UHP. Interestingly, the corresponding cobalt(salen) complexes in a
trans
- confi guration show no asymmetric induction. Aoki and Seebach have also reported
that the regulation of Criegee intermediate is essential for chiral alkyl hydroperoxide-
mediated Baeyer - Villiger oxidation [123] .
β
