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N
N
N
COOH
OH
H
H
N
H
HN
O
91
[105]
59
[1 06]
92
[107]
CH
3
CH
3
BocHN
N
N
N
N
N
COOH
N
Bn
H
H
H
H
Bn
H
COOH
m
O
93
[108]
m=2-3
95
[110]
94
[1 09]
N
HN
BocHN
O
N
COOH
H
2
N
H
COOH
H
NH
O
96
[111]
97
[112]
Figure 8A.5.
8A.3.3. Conjugate Addition of Nitroalkanes
Aminocarbonyl compounds, aminoalkanes, and pyrrolidines can be produced from
asymmetric conjugate additions of nitroalkanes to
- unsaturated ketones. A variety
of chiral amines were applied in the conjugation reaction of nitroalkanes with cyclic and
acyclic enones (Fig. 8A.5 ).
Warrier and others reported the conjugate addition of 2-nitroalkanes to 2-cycloalke-
nones by applying
91
as catalyst with up to 99% ee (Scheme 8A.50) [105].
α
,
β
O
O
91
(10% mmol)
trans
-2,5-dimethylpiperazine
CHCl
3
,rt
n
n
=0,1,2
n
n
=0,1,2
NO
2
O
2
N
Up to 99% ee
Scheme 8A.50.
Jørgensen et al. [108,109] applied a new imidazolidine catalyst
93
for the enantioselec-
tive conjugate addition of nitroalkanes to α , β-unsaturated enones. A new, more soluble
organocatalyst
94
was developed to improve the rate of reaction and enantioselectivity
(Scheme 8A.51 ) [109] .
A useful organocatalyst pyrrolidine-tetrazole
59
in combination with
trans
- 2,5 -
dimethylpiperazine as additive was applied in the conjugate addition of a variety of
nitroalkanes to cyclic and acyclic enones with high enantioselectivities (94-97% ee)
(Scheme 8A.52 ) [106] .
