Methyl iodide (0.214 mL, 3.43 mmol) was added to a suspension of tert-butyl (6R,7R)-6-(2-amino-2-thioxoethyl)-7-(3,4-dichlorophenyl)-1,4-oxazepane-4-carboxylate (288 mg, 0.69 mmol) and potassium carbonate (142 mg, 1.03 mmol) in acetone (5 mL) at room temperature. The reaction mixture was stirred at room temperature for 4 hr, 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 dissolved in toluene (5 ml), acetohydrazide (61.1 mg, 0.82 mmol) was added, and the mixture was stirred at 120° C. overnight while using a Dean-Stark trap. To the reaction mixture 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 (241 mg, 0.545 mmol, 79%).
