Sulfuryl chloride (0.094 mL, 1.16 mmol) was added to a solution of tert-butyl (6R,7R)-7-(3,4-dichlorophenyl)-6-(4-ethoxy-2,4-dioxobutyl)-1,4-oxazepane-4-carboxylate (500 mg, 1.05 mmol) in toluene (5 mL). The reaction mixture was stirred at room temperature for 45 min, and concentrated under reduced pressure. To the residue were added ethanol (5 ml) and thioacetamide (87 mg, 1.16 mmol), and the mixture was stirred at 80° C. for 1.5 hr. To the reaction mixture were added triethylamine (0.294 mL, 2.11 mmol) and di-tert-butyl dicarbonate (0.291 ml, 1.26 mmol) at room temperature, and the mixture was stirred at room temperature for 30 min, and concentrated under reduced pressure. To the residue was added aqueous sodium hydrogen carbonate solution, and the mixture was extracted with ethyl acetate. The extract was washed with brine, and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography to give the title compound (358 mg).
