A New Preparative Route to 3-Unsubstituted Cephalosporins From Penicillin V

Abstract

p- Nitrobenzyl (2R,3R)-2-(benzothiazol-2′-yldithio)-α-isopropylidene-4- oxo-3-phenoxyacetyl-aminoazetidine-1-acetate (7), readily prepared from penicillin V, can be converted into the corresponding 2-allylthio compound (2) by addition of allyl bromide and sodium borohydride at a low temperature. This compound (2) on treatment with ozone, followed by cyclization with trimethyl phosphite, produces a 3H-ceph-3-em ester (4). The ester can be easily de-esterified to the free acid (1b).