4.2 ml (30 mmoles) of triethylamine and 3.28 g (24 mmoles) of N-bromosuccinimide were sequentially added to a solution of 7.8 g (20 mmoles) of t-butyl 7-benzamido-3-methyl-3-cephem-4-carboxylate 1-oxide in 150 ml of methylene chloride under nitrogen and cooled in an ice bath and the mixture was irradiated with a 150 W tungsten lamp for 15 minutes. The dark-brown reaction mixture was washed with a dilute hydrochloric acid solution (pH 1) and then twice with 250 ml portions of water. The organic layer was dried over magnesium sulfate, filtered and evaporated to dryness to obtain 10.6 g (70% yield-purity 62%) of t-butyl 7-benzamido-2-bromo-3-methyl-3-cephem-4-carboxylate 1-oxide.
