Enantioselective organocatalytic reductions

An enantioselective organocatalytic reductive amination has been achieved using Hantzsch ester for hydrogen transfer and compound (21) as catalyst. This mild and operationally simple fragment coupling has been accomplished with a wide range of ketones in combination with aryl and heterocyclic amines.359... 

Development of the First Highly Enantioselective Organocatalytic Reduction of Ketimines... 

The same approach was used by Benagha s group for the enantioselective organocatalytic reduction of P-trifluoromethyl nitroaUcenes 73, with the aim of achieving chiral yS-trifluoromethyl amines 75 (Scheme 28) [161]. The authors also performed the organocatalyzed reduction of a-substituted-p-trifluoromethyl nitroalkenes, although with poorer results. The stereochemical result of the reaction and the behavior of thiourea catalyst 74 were discussed based on computational studies and DFT transition-state analysis. 

Although natural amino acids are readily available, there is a continuing need for unnatural amino acids. Jon C. AntiUa of the University of South Florida has described J. Am. Chem. Soc. 2007,129, 5830) a promising approach, based on the enantioselective organocatalytic reduction of imines such as 1 derived from a-keto esters. The aryl group is easily removed to give the primary amine. 

During the study on enantioselective organocatalytic reductive amination, MacMillan et al. found that the pyruvic acid-derived cyclic imino ester could be efficiently reduced to yield the corresponding alanine amino ester with 97% ee and 82% yield... 

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