4-(Phenylsulfonylthio)-2-azetidinones have been prepared conveniently by the reaction of 4- (2-benzothiazolyldithio)-2-azetidinones with 2-benzothiazolyl benzenethiosulfonates. A combination of this reaction with the electrolytic cross-coupling of bis (benzothiazolyl) disulfide and ammonium benzenesulfinate can establish a recycling system, in which S-(2- benzothiazolyl) benzenethiosulfonate is regenerated to play a critical role in penicillin– ...