STUDIES ON LACTAMS .87. STEREOREGULATED SYNTHESIS OF BETA-LACTAMS FROM SCHIFF-BASES DERIVED FROM THREONINE ESTERS

A variety of optically active 3-substituted-2-azetidinones has been prepared by the annelation of Schiff bases derived from cinnamaldehyde and D-threonine esters and their absolute configuration determined. When the beta-hydroxyl group of threonine is unprotected, both enantiomeric forms of N-unsubstituted 3,4-disubstituted-2-azetidinones can be prepared from a single beta-lactam-forming reaction. On the other hand, by converting the hydroxyl group of D-threonine to a bulky group (e.g., triphenylsilyl ether), very high diastereoselectivity can be induced. The multiple functional groups on these beta-lactams can be easily modified to generate useful synthons for optically active sugars, alkaloids. and monocyclic and bicyclic beta-lactam antibiotics,