To a solution of p-nitrobenzyl α-[4-carbobenzoxythio-3-phenoxyacetamido-2-oxoazetidin-1-yl]-α-(2-bromo-1-hydroxyethylidene)acetate (480 mg) in methylene chloride (5 ml) containing 20% of nitromethane is added a solution of aluminum chloride (270 mg) in methylene chloride containing 20% of nitromethane (4 ml), and the mixture is stirred at room temperature for 1 hour. The reaction mixture is poured into diluted hydrochloric acid, and is extracted with methylene chloride. The extract solution is washed water, dried over magnesium sulfate, and evaporated to give p-nitrobenzyl α-[4-mercapto-3-phenoxyacetamido-2-oxoazetidin-1-yl]-α-(2-bromo-1-hydroxyethylidene)acetate (376 mg). Yield: 99.5%.
