A novel one-step diastereo- and enantioselective formation of trans-azetidinones and its application to the total synthesis of cholesterol absorptioninhibitors

An efficient and practical asymmetric process was developed for the synthes is of azetidinone-based cholesterol absorption inhibitors. Key to this synt hesis was the discovery of a novel one-step diastereo- and enantioselective formation of trans p-lactams starting from commercially available 3(S)-hyd roxy-gamma-lactone. Various trans a-lactams can be prepared in good yields and with better than 95:5 enantio- and diastereoselctivity. A Lewis acid-ca talyzed aldol condensation and a highly enantioselective oxazaborolidine-ca talyzed chiral reduction completes the side chain.