Improved Methodology for the Preparation of Chiral Amines

1). They described the role of each functional group in the catalyst and its importance in
controlling stereoselectivity. They also marked the important structural features in the imine
which controls the total outcome of the reaction. They tested their system also for the
reduction of substituted phenyl methyl N-aryl imines. p-OMe (85% ee, 86% yield), p-CF 3
(89% ee, 86% yield), o-Me (92% ee, 90% yield) phenyl, methyl N-aryl imines were
successfully reduced (structure 3, figure 2.3).
In 2007 he reported the use of his catalyst with fluorous tag for imine reduction. [37] Fluorous
tags are used to enable recycling of the catalyst. He was able to reuse the catalyst 4-5 times
without significant loss of enantioselectivity and yield. Using 10 mol % of valine derived
catalyst (catalyst 19, figure 2.4), 2.0 equiv of HSiCl 3 , toluene, 18 °C, 16 h, the ee was 90%
with 98% yield for phenyl methyl N-aryl imine (structure 1, figure 2.3). p-CF 3 (92% ee, 72%
yield, 10 °C) and p-OMe (84% ee, 84% yield) phenyl methyl N-aryl imines were reduced
with high yields and ees (structure 3, figure 2.3). 2-naphthyl methyl N-aryl imine was
reduced with 92% ee and 93% yield.
In 2008 he reported the use of his catalyst with polymer support, which can be used up to 5
times without significant loss of catalyst activity. [38] Using 15 mol % of the catalyst (catalyst
20, figure 2.4), 2.0 equiv Cl 3 SiH, CH 3 Cl, 25 °C, 16 h, the ee was 82% with 84% yield for
phenyl methyl N-aryl imine (structure 1, figure 2.3). He expanded his study to cover other
substituted phenyl methyl N-aryl imines. p-OMe (77% ee, 63% yield) and p-CF 3 (81% ee,
67% yield) phenyl methyl N-aryl imines were reduced. Also 2,5 Me-3-furyl phenyl, methyl
N-aryl imine was reduced with 78% ee and 67% yield (structure 3, figure 2.3).
In 2006 he introduced the use of oxazoline catalyst for reduction of N-aryl imines. [39] Using
20 mol % of the catalyst (catalyst 18, figure 2.4), 2.0 equiv of HSiCl 3 , CHCl 3 , –20 °C, 24 h,
resulted in 87% ee and 65% yield phenyl methyl N-aryl imine (structure 1, figure 2.3). p-
OMe (87% ee, 51% yield) and p-CF 3 (87% ee, 65% yield) phenyl methyl N-aryl imines were
reduced successfully (structure 3, figure 2.3).
The group of Sun also prepared several organocatalysts for the hydrosilylation of imines. In
2006, they tested pipecolinic acid derived formamides catalyst. [40] Using 10 mol % of the
catalyst (catalyst 21, figure 2.4), 2.0 equiv of Cl 3 SiH, CH 2 Cl 2 , 0 °C, 16 h, the ee was 95%
47