8 N Aqueous sodium hydroxide solution (0.620 mL) was added to a solution of tert-butyl (6R,7R)-6-(2-amino-2-oxoethyl)-7-(3,4-dichlorophenyl)-1,4-oxazepane-4-carboxylate (500 mg) in n-butanol (5 mL), and the mixture was stirred at 120° C. for 4.5 hr. The reaction mixture was neutralized with 1 N hydrochloric acid, 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 (434 mg).
