Chemistry Reference
In-Depth Information
process.
47
Aerial oxygen acts as the terminal oxidant to produce the a,b-
unsaturated aldehyde and the additive pyridine base plays the role of an
organocatalyst for the isomerization reaction (Figure 2.7). The rate of the
reaction is accelerated in the presence of dimethylaminopyridine (DMAP)
instead of NMI in acetonitrile.
The Cu-TEMPO catalytic system has been used to oxidize aromatic amino
alcohols to quinolines and indoles by a combination of copper(
II
) triflate,
2,2
0
-bipyridine, TEMPO, DBU and NMI in acetonitrile under air at 60 1C.
48
A
practical method for oxidative imine synthesis from alcohol and amine by
using the (bpy)Cu(
I
)-TEMPO system has been developed (Figure 2.8).
49
Several N-donor ligands other than bpy have been studied to develop the
Cu-TEMPO based alcohol oxidation catalyst. Jiang and Ragauskas reported a
four-component system consisting of acetamido-TEMPO (C in Figure 2.2)-
Cu(ClO
4
)
2
-TMDP-DABCO (TMDP
ΒΌ
trimethylenedipyridine) for the oxidative
catalysis of benzylic and allylic alcohols in dimethyl sulfoxide (DMSO)
(Figure 2.9a). The catalytic system works for a wide range of alcohols with
good to excellent yields of the corresponding carbonyl compounds under
ambient conditions. Moreover, the catalyst could be recycled and reused
d
n
4
r
4
n
g
|
0
Cu
I
/TEMPO/diMeObpy (1 mol%)
DMAP (2 mol%)
R
2
R
2
Z E
I
somerizatio
n
Cu-catalyzed
oxidation
O
2
, MeCN, RT
R
2
CH
2
OH
R
1
CHO
CHO
R
1
.
R
1
Z
Z
E
diMeObpy : 4,4'-dimethoxy-2,2'-bipyridine
Figure 2.7 One-pot oxidation-isomerization of (Z)-allylic alcohol under aerobic
conditions.
R
1
OH
R
2
R
1
N
+
+
H
2
O
R
2
NH
2
CuI (1 mol%)
bpy (1 mol%)
TEMPO (2 mol%)
CH
3
CN, air, RT, 6-12 h
Ph
OH
R
2
+H
2
O
+
Ph
N
R
2
NH
2
Figure 2.8 Cu-catalyzed oxidative syntheses of imines from alcohols.
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