BETA-LACTAMS FROM ESTER ENOLATES AND SILYLIMINES - AN ENANTIOSPECIFIC SYNTHESIS OF MONOCYCLIC BETA-LACTAMS

Optically active 3,4-disubstituted azetidin-2-ones have been prepared by annelation of chiral silylimines derived from (S) or (R)-lactaldehyde with the ester enolate of the ethyl 2,2,5,5,-tetramethyl-1,2,5-azadisilolidin-1-acetate (STABASE). Oxidation of the hydroxyethyl side chain on the C-4 position of the beta-lactam ring, followed by Baeyer-Villiger oxidation led to the optically active (3S, 4S) 3-amino-4-acetoxy-beta-lactam. The absolute configuration of this compound was determined by elaboration of this substrate to a key intermediate in the synthesis of the antibiotic ''Aztreonam''. Nucleophilic displacement of the acetoxy group led to optically active 3-amino-4-alkyl (aryl)-azetidin-2-ones.