Radical Cyclization Approach to 4-Oxo-2-azetidineacetic Acids: Synthesis of a Chiral Key Intermediate for Carbapenem Antibiotic PS-5

Abstract

α-Bromo amide 8 bearing phenyl and phenylthio substituents at the terminus of the N-vinylic bond underwent radical cyclization in a 4-exo-trig manner to give β-lactam 9, which was transformed, via oxidation of its phenyl group, into the key intermediate 14 for the synthesis of (±)-PS-5. The chiral key intermediate 23 for (+)-PS-5 was also obtained via an asymmetric radical cyclization of bromide 16 bearing (S)-1-phenylethyl group on the nitrogen atom.