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H
H
N
OH
Br
Br
OH
H
N
N
OBn
N
N
H
OH
OBn
OCH
3
N
75
[87]
OBn
74
[86]
73
[85]
OCH
3
OCH
3
N
Ph
N
N
OH
O
O
N
OMe
H
3
CO
NN
OCH
3
N
H
N
Ph
N
N
76
[88]
78
[88]
77
[8 8]
Figure 8A.2.
organocatalytic conjugate addition of ketones under homogeneous and phase-transfer
catalyst (PTC) conditions, delivering different enantiomerically enriched compounds.
For example,
Cinchona
alkaloid-derived catalysts such as
73 - 78
were applied success-
fully in asymmetric conjugate addition (Fig. 8A.2).
Catalyst
56
was recently employed in the conjugate addition of six-membered-ring
ketones to
-unsaturated ketones, affording synthetically useful 1,5-dicarbonyl com-
pounds (Scheme 8A.48 ) [89] .
α
,
β
Ar
1
O
O
O
O
56
(10 mol %
)
Ar
2
+
NHSO
2
CF
3
Ar
1
Ar
2
i
Pr OH
,rt
X
H
X
56
Up to 89% yield
Up to 97% ee
X=CH
2
,NH,O
Scheme 8A.48.
Some of the chiral amines such as
59
,
60
,
64
, and
79 - 89
were also very effi cient for
the addition of six-membered-ring ketones to
- nitrostyrene and derivatives (Fig. 8A.3 ).
Huang and Jacobsen described a new catalyst
90
for the asymmetric conjugate addi-
tion of different aliphatic ketones with not only nitrostyrenes but also nitroalkenes
bearing aliphatic
β
- substituents (Scheme 8A.49 ) [104] .
A bifunctional mechanism promoted by catalyst
90
was proposed in this reaction.
The authors pointed out that
anti
diastereoselectivity indicated the participation of a
Z
- enamine intermediate (Fig. 8A.4 ).
β
