Chemistry Reference
In-Depth Information
Table 16.4
Bifunctional amine-thiourea
10b
-catalyzed nitro-Mannich reaction.
Boc
Boc
N
15 mol%
10b
CH
2
Cl
2
, -78 °C
HN
CH
3
NO
2
+
NO
2
Ar
Ar
H
Ar
Yield (%)
ee (%)
Ph
86
>
99
4-MeOC
6
H
4
94
94
4-MeC
6
H
4
93
83
4-ClC
6
H
4
93
>
99
3-FC
6
H
4
87
>
99
4-FC
6
H
4
91
>
99
2-ClC
6
H
4
85
92
1-Naphthyl
95
>
99
2-Furyl
86
90
4-F
3
CC
6
H
4
85
94
2-F
3
CC
6
H
4
84
96
16.3
Michael Additions
The conjugate addition of nucleophiles to electron-deficient olefins is an important
tool for the construction of highly functionalized carbon skeletons. Among the
variants of these Michael additions, the direct catalytic addition of carbonyl com-
pounds to
unsaturated nitroolefins is one of the most facile routes to produce
useful building blocks in an atom-economical manner [24]. In the last decade,
several small organic molecules have been developed as efficient organocatalysts
for asymmetric conjugate additions of aldehydes and ketones as well as more
reactive nucleophiles, such as malonic esters, ketoesters, 1,3-diketones, and 1,3-
dinitriles to nitroolefins [25]. Very recently, carbohydrate derivatives have also been
elaborated into successful organocatalysts for several Michael addition reactions.
α
-
β
16.3.1
Bifunctional Primary Amino-Thiourea Catalysts
In 2006, Ma's group described enantioselective conjugate addition of aromatic
methyl ketones to
-
trans
-nitrostyrenes by using chiral bifunctional primary
amine-thioureas [26]. These organocatalysts were readily prepared from commer-
cially available carbohydrates and 1,2-cyclohexanediamine (Scheme 16.5). In the
presence of optimized organocatalyst
11b,
good to excellent enantioselectivities
were achieved for various aromatic nitroolefins and substituted acetophenones.
High stereoselectivity was also observed with alkyl-substituted nitroolefins, albeit
in low yield (Table 16.5).
β
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