Synthesis of 4-oxo-2-azetidineacetic acids by means of radical cyclization of N-vinylic α-bromo amides

Article abstract of DOI:10.1016/0040-4020(96)00849-6

Bu₂SnH-mediated radical cyclization of α-bromo amide 8, bearing phenyl and phenylthio substituents at the terminus of the N-vinylic bond, proceeded in a 4-exo-trig manner to give β-lactam 9. Ruthenium tetroxide oxidation of the phenyl group incorporated into the product 9 provided a new synthesis of 4-oxo-2-azetidineacetic acid 13, a useful intermediate for (±)-PS-5. Chiral 4-oxo-2-azetidineacetic acids 23 and 36, key intermediates for the synthesis of (+)-PS-5 and (+)-thienamycin, respectively, were also obtained through the asymmetric radical cyclization of N-vinylic α-bromo amides having chiral auxillaries at the side-chain.