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OH
O
1 mol% VOCl
3
, O
2
MeCN, rt
R'
R'
R
R
O
O
d
n
4
r
4
n
g
|
5
Scheme 6.10 Aerobic oxidation of a-hydroxycarbonyls catalyzed by VOCl
3
.
5 mol% VO(O
i
-Pr)
3
, 5.5 mol%
L
O
OH
OH
O
2
OR
2
OR
2
OR
2
R
1
+
R
1
R
1
acetone
O
O
O
t
-Bu
50~99%ee
N
OH
t
-Bu
OH
L
=
t
-Bu
Scheme 6.11 Oxidative kinetic resolution of a-hydroxy esters catalyzed by VO(OiPr)
3
and chiral O,N,O-chelating tridentate ligands.
-Bu
t
O
O
N
O
V
OCH
3
R
1
O
O
5 mol%
O
H
CH
3
OH
OH
R
2
XR'
XR'
.
XR'
+
R
R
R
O
2
, toluene
O
O
O
t
-Bu
O
O
N
O
V
OCH
3
Br
O
5 mol%
O
OH
CH
3
OH
O
H
OBn
OBn
OBn
OBn
OBn
OBn
Br
R
P
O
+
R
P
O
R
P
O
O
2
, toluene
Scheme 6.12 Oxidative kinetic resolution of a-hydroxy esters, -amides and -phos-
phonates catalyzed by chiral vanadyl carboxylates.
racemic a-hydroxy esters, -amides and thioesters with excellent selectivity
factors (k
rel
ΒΌ
40 to 4500) (Scheme 6.13).
Subsequently, Chen's group prepared polystyrene-supported chiral
vanadyl catalysts through the click chemistry approach.
20
These catalysts
promoted the asymmetric aerobic oxidation of a-hydroxy (thio)esters
and -amides with enantioselectivities of up to 99%ee in chloroform
(Scheme 6.14). These catalysts can be readily recovered by filtration and
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