New, Readily Available Organocatalysts for the Enantioselective Reduction of α-Imino- and β-Imino Esters

Novel metal-free, readily available chiral catalytic systems for the enantioselective reduction of keto imines are reported. Different beta-imino esters were reduced by trichlorosilane in the presence of 10 mol% of a chiral Lewis base easily obtained in one step only from prolinol, in high yields and in up to 85% enantioselectivity; imines bearing an inexpensive and removable chiral auxiliary, were reduced with complete control of the absolute stereochemistry. The methodology was successfully extended to the stereoselective synthesis of alpha-amino esters.