A Cation-exchange Resin Promoted Imino Aldol Reaction, Leading to the Synthesis of 2-Isocephem and 2-Oxa-isocephem

Imino aldol reaction of ketene silyl acetals with the chiral imine 1 proceeds smoothly to give(beta)-amino esters in good yields with high diasetereoselectivity under the influence of a cation-exchange resin, and the subsequent functional group transformations provide a formal synthesis of 2-isocephem and 2-oxa-isocephem (beta)-lactam antibiotics.