Synthetic studies on optically active .BETA.-lactams. II. Asymmetric synthesis of .BETA.-lactams by (2+2)cyclocondensation using heterocyclic compounds derived from L-(+)-tartaric acid, (S)- or (R)-glutamic acid, and (S)-serine as chiral auxiliaries.

Abstract

Asymmetric synthesis of β-lactams by the [2+2]cyclocondensation of an imine (7) to chiral ketene species (2b, 4b, and 6c) bearing heterocycles derived from L-(+)-tartaric acid, (S)-glutamic acid, and (S)-serine was carried out. The reaction of 2b with 7 gave the trans-β-lactams with 74% diastereomeric excess, and cis-β-lactams were predominantly formed with high diastereomeric purity (up to 96%) when 4b and 6c were employed. Asymmetric synthesis of (3S, 4S)- and (3R, 4R)-1-benzyl-3[(benzyloxycarbonyl)amino]-4-hydroxymethyl-2-azetidinones (26 and 30g) using (R)-4b as a ketene species and the chiral imine (21) prepared from L-(+)-tartaric acid was also achieved.