ASYMMETRIC PUMMERER-TYPE REACTIONS INDUCED BY O-SILYLATED KETENE ACETALS

O-Silylated ketene acetals are effective reagents for the asymmetric P ummerer-type rearrangement and the asymmetric intramolecular Pummerer- type cyclization of chiral, non-racemic sulfoxides. The reactions proc eed smoothly in the presence or absence of a catalytic amount of zinc iodide or zinc chloride in acetonitrile, tetrahydrofuran or dichlorome thane. These Pummerer-type reactions show the highest optical inductio n of all previously examined methods. Moreover, the reaction can be ap plied to an asymmetric synthesis of beta-lactam antibiotics.