Asymmetric Synthesis of Chiral gamma- and delta-Amino Esters Using Trichlorosilane Activated with a Lewis Base Catalyst

Abstract

Novel chiral gamma- and delta- amino esters 2 a-k were synthesized by enantioselective reduction of N-aryl gamma- and delta-imino esters with aryl, substituted aryl, and heteroaryl groups 1 a-k using trichlorosilane activated with optically active N-pivaloyl L-proline I in high yields (50%-98%) with enantioselectivities (10%-84% enantiomeric excess). The structures of the chiral amino esters 2 a-k were clarified by infrared, nuclear magnetic resonance (H-1 and C-13) and gas chromatography-mass spectrometry. The enantiomeric excess of these compounds were identified by chiral high-performance liquid chromatography using a Chiralpak AD-H column. The highest ee of 84% and highest yield of 98% were found for 2 d.