Asymmetric synthesis of 1,3,4-trisubstituted and 3,4-disubstituted 2-azetidinones: strategy based on use of D-glucosamine as a chiral auxiliary in the Staudinger reaction

An efficient asymmetric approach to the synthesis of trisubstituted azetidin-2-ones is presented. The strategy relies on the use of ketene–imine cycloaddition between ketenes generated from phthalimidoacetic and methoxyacetic acids and a chiral Schiff base (3) derived from 3,4;5,6-di-O-isopropylidene-D-glucosamine propane dithioacetal (2) and cinnamaldehyde; the removal of the chiral auxiliary group by β-elimination is a noteworthy facet of this communication.