A CONTRIBUTION TO THE CONFUSION SURROUNDING THE REACTION OF KETENES WITH IMINES TO PRODUCE BETA-LACTAMS - A COMPARISON OF STEREOSELECTIVITY DEPENDENCE ON THE METHOD OF KETENE GENERATION - ACID CHLORIDE TRIETHYLAMINE VS PHOTOLYSIS OF CHROMIUM CARBENE COMPLEXES

The stereoselectivity of the reaction of imines of benzaldehyde and cinnamaldehyde with ketenes generated by the reaction of optically active oxazolidinone acid chlorides with triethylamine and complexed ketenes generated by photolysis of optically active oxazolidine- and oxazolidinone-chromium-carbene complexes in the presence and absence of added triethylamine was compared. The absolute stereochemistry was determined primarily by the structure of the chiral auxiliary. The relative (cis-trans) stereochemistry was determined primarily by the structure of the imine and the free or bound character of the ketene. Triethylamine addition to reactions of carbene complexes afforded results that closely paralleled that of acid chloride generated ketenes. A mechanistic scheme accounting for these results and the general trends observed in other ketene/imine cyclizations is provided.