AN APPROACH TO CLAVAMS AND 1-OXACEPHAMS FROM HYDROXY-ACIDS

[2 + 2] Cycloaddition of chlorosulfonyl isocyanate to chiral alkyl vin yl ethers bearing a sterogenic center in the alkyl part of the ether a fford the corresponding azetidin-2-ones with relatively good asymmetri c induction in certain cases. Reactions were shown to depend on steric requirements of the ligands at the stereogenic center. The model that rationalizes the stereochemical outcome is based on the s-cis conform ation of the vinyl ether in which the bulkiest of the ligands is situa ted in the plane of the double bond, and the next most demanding subst ituent is placed gauche to the double bond.