Stereoselective synthesis of N-phenylsulfonyl substituted spiro-beta-lactams

A stereoselective synthesis of N-phenylsulfonyl substituted spiro-\u3b2- lactams obtained from the N-(phenylmethylene)benzenesulfonamide and the ketene valence tautomer of the bicyclic mesoionic compounds derived from 4- hydroxy substituted N-acyl-L-prolines in the presence of acetic anhydride as the dehydrating agent is presented. The reaction of (2S,4R)-4-acetyloxy or benzoyloxy-N-acyl-proline with the above imine afforded a mixture of two diastereoisomeric spiro-\u3b2-lactams with complete stereoselectivity for the spiro carbon