Structural and electronic effects of oxazolidine ligands derived from (1 R,2 S)-ephedrine in the asymmetric addition of diethylzinc to aldehydes

Abstract

The purpose of this research was to determine the activity of chiral oxazolidine ligands prepared from (1 R,2 S)-ephedrine for the enantioselective addition of diethylzinc to aldehydes. The configuration on the newly formed C2 stereogenic center was determined as (2 S) by X-ray structural analysis. Oxazolidine ligands reveal medium enantioselectivity with the ee exceeding 57%, and the yields obtained being 68–99%. The results indicate that the absolute configuration of the addition product depends not only on the N3-methyl as an important stereocontrol element but also on both the electronic and steric effects of the substrates and oxazolidine ligands.