Synthesis and Characterization of N-Substituted (S)-1,2,3,4-Tetrahydroisoquinoline-3-carboxamides and Thioamides as Organocatalysts for Asymmetric Aldol Reaction

Abstract

In this paper, the preparation and characterization of eight optically pure N-functionalized (S)-1,2,3,4-tetrahydroisoquinoline-3-carboxamides and thioamides is described. The prepared amides and thioamides were tested as organocatalysts of aldol reaction of 4-nitrobenzaldehyde and acetone. The highest ee of formation of 4-hydroxy-4-(4-nitrophenyl)butan-2-one was obtained with (S)-N-[(1R)-1-phenylethyl]-1,2,3,4-tetrahydroisoquinoline-3-thiocarboxamide (77% ee). The observed deceleration of the aldol reaction catalyzed in this way, as compared with that catalyzed with (S)-proline, was attributed to the formation of little reactive cyclic intermediate, which was isolated and characterized.