Chiral Cyclobutane Synthesis by Exploiting a Heteroatom-Directed Conjugate Addition

The syntheses of both enantiomers of cyclobutanes B and ent-B are achieved through heteroatom-directed conjugate addition (HADCA) of nucleophiles to the epoxyvinylsulfone-substituted carbohydrates A and ent-A, which provided carbanions that intramolecularly attacked the epoxide with concomitant formation of the cyclobutane ring.