Chiral C-2-symmetric 2,3-disubstituted aziridine and 2,6-disubstituted piperidine as chiral ligands in the addition reaction of diethylzine with arylaldehydes

Chiral C-2-symmetric 2,3-disubstituted aziridines and 2,6-disubstituted pip eridines having a p-amino alcohol moiety have been successfully synthesized and their catalytic chiral induction properties have been examined in the asymmetric addition reactions of diethylzinc with arylaldehydes in hexane. When N-(2,2-diphenyl-2-hydroxyethyl)-(S,S)-2,3-bis(methoxymethyl)aziridine III was used as a catalytic chiral ligand, sec-alcohols having (S)-configur ation formed in high yields of 86-92% but low enantiomeric excesses (ee's) of 11-13%. However, when N-(2,2-diphenyl-2-hydroxyethyl)-(R,R)-2,6-disubsti tuted piperidine derivatives 16 and 20 were used as the chiral ligands unde r the same reaction conditions, the ee's of the corresponding sec-alcohols were 20-30 and 5-6%, respectively, along with the inversion of absolute con figuration. A plausible mechanism for this inversion is proposed. (C) 2001 Elsevier Science Ltd. All rights reserved.