PREPARATION OF 3-ALKYL BETA-LACTAMS VIA THE KETENE IMINE CYCLOADDITION REACTION USING ALPHA-(PHENYLTHIO)ALKANOYL HALIDES AS STARTING MATERIALS - APPLICATION TO THE SYNTHESIS OF (+/-)-CARBAPENEM BUILDING-BLOCKS AND RELATED-COMPOUNDS

Preparation of appropriately substituted 3-alkyl beta-lactams via the ketene (or equivalent)-imine cycloaddition reaction is described. The dehydrochlorination reaction of alpha-(phenylthio)alkanoyl chlorides with triethylamine in the presence of imines derived from cinnamaldehydes and p-anisidine produced a high-yield formation of alpha-phenylthio beta-lactams, which upon desulfuration furnished a variety of 3-alkyl beta-lactams in a highly stereoselective fashion. In contrast, reaction between alpha-haloalkanoyl chlorides and cinnamylideneamines in the presence of triethylamine furnished the corresponding [4 + 2] cycloadducts as main products. Preparation of highly functionalized alpha-alkylidene beta-lactams through thermal decomposition of the corresponding beta-lactam sulfoxides or by cycloaddition of alpha,beta-unsaturated acid chlorides to imino esters in the presence of triethylamine is also described. Addition of Flemming's silylcuprate reagent to alpha-alkylidene beta-lactams furnished the corresponding 3-(1'-(dimethylphenylsilyl(ethyl) beta-lactams as (+/-)-thienamycin intermediates.