Chemistry Reference
In-Depth Information
R
1
R
1
4 mol% Cu(ClO
4
)
2
, 4 mol% TMDP
6 mol% acetamido-TEMPO, O
2
10 mol% DABCO, DMSO, RT
(a)
OH
O
R
2
R
2
d
n
4
r
4
n
g
|
0
(b)
R
1
R
1
XH
Y
CuCl/DABCO/4-HO-TEMPO
R
2
+
CHO
O
2
, CH
3
CN, 80
o
C
NH
2
R
2
N
X = NH, O
Y = N, O
R
1
= H, Cl, Me
R
2
= Alkyl, Aryl, Heterocyclic
DABCO :
N
N
Figure 2.9
(a) Aerobic oxidation of alcohols using acetamido-TEMPO-Cu(ClO
4
)
2
-
TMDP-DABCO catalyst system; (b) aerobic oxidative synthesis of 2-substi-
tuted quinazolines and 4H-3,1-benzoxazines.
OH
O
OH
Cu(OTf)
2
(5 mol%)
(
R
)- BINAM (10 mol%)
TEMPO (5 mol%)
*
+
toluene, O
2
, 80
o
C
H
2
N
H
2
N
H
2
N
(
+
)
NR
1
R
2
NR
1
R
2
BINAM :
.
Figure 2.10 Oxidative kinetic resolution of amino alcohols by (BINAM)Cu-TEMPO
catalyst.
three times without appreciable loss of catalytic activity, simply extracting
the final products with n-pentane and adding fresh alcohol to the DMSO
phase.
50
A catalyst containing a mixture of DABCO, CuCl and TEMPO (5 mol%
each) has been reported that exhibits remarkable conversion of both primary
and secondary alcohols to the corresponding carbonyl compounds in toluene
at 100 1C.
51
Single-crystal X-ray examination revealed the copper(
II
)centerina
trigonal bipyramidal coordination geometry in the related catalytic complex
[(DABCO)
2
CuCl
2
HCl]. Recently, this catalytic system in combination with
4-hydroxy-TEMPO (B in Figure 2.2) was used to carry out the oxidative
synthesis of heteroaromatic compounds such as 2-substituted quinazolines
and 4H-3,1-benzoxazines in acetonitrile (Figure 2.9b).
52
An enantiopure bidentate nitrogen donor ligand, (R)-BINAM, was used in
the Cu(OTf)
2
-TEMPO-catalyzed oxidative kinetic resolution (OKR) of several
benzylic amino alcohols (Figure 2.10).
53,54
The use of an isolated copper(
II
) complex of 1,10-phenanthroline (phen) in
combination with a stable nitroxyl radical (di-tert-butylnitroxyl) for the
catalytic aerobic oxidation of alcohols was first reported by Bracksman and
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