A STEREOCONTROLLED METHOD FOR THE SYNTHESIS OF EACH OF THE 4 DIASTEREOMERS OF 3,4-DIALKYL-SUBSTITUTED BETA-LACTAMS USING DIFFERENT METAL ESTER ENOLATES AND A CHIRAL IMINE

The reaction of the different metal ester enolates of t-butyl alpha-alkyl substituted acetates with a chiral imine possessing a dioxolane ring derived from (2S,3S)-1,4-dimethoxy-2,3-butanediol as a chiral auxiliary followed by cyclization of the initial products of beta-amino esters gave each of the diastereomers of 3,4-dialkyl-substituted beta-lactams in a highly stereoselective manner, i.e., the titanium enolate gave trans-(3R,4S)-isomer, while the lithium and zinc ones afforded cis-(3S,4S)- and (3R,4R)-isomers, respectively, and the cis-(3R,4R)-beta-lactams thus obtained were readily epimerized to the corresponding trans-(3S,4R)-beta-lactams without loss of the stereochemical integrity at C4.