To a solution of tert-butyl (6R,7S)-6-amino-7-(3,4-dichlorophenyl)-1,4-oxazepane-4-carboxylate (100 mg) in THF (2 mL) was added benzyl bromide (0.036 mL) at 50° C., and the mixture was stirred at 50° C. overnight. The reaction mixture was diluted with ethyl acetate. The diluted solution was washed with brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure, and the residue was purified by silica gel chromatography (hexane/ethyl acetate) to give the title compound (80 mg).
