Under nitrogen, to a suspension of sodium hydride (60% in oil, 12 mg) in N,N-dimethylformamide (2 ml) was dropwise added N-(3-hydroxy-6,7,8,9-tetrahydro-5H-benzocyclohepten-6-yl)-N-[(2S)-3-phenoxy-2-(triethylsilyloxy)propyl]-tert-butoxycarbonylamine (150 mg) in N,N-dimethylformamide (1 ml) at 5° C., and the mixture was stirred at the same temperature for 30 minutes. To this one was added ethyl iodide (27 μl), and the mixture was stirred at room temperature for 2 hours. The resulting mixture was poured into saturated aqueous sodium hydrogencarbonate, and extracted with ethyl acetate. The organic layer was washed with brine, dried over anhydrous magnesium sulfate, and evaporated in vacuo. The residue was purified by column chromatography on silica gel (hexane:ethyl acetate=20:1) to give N-(3-ethoxy-6,7,8,9-tetrahydro-5H-benzocyclohepten-6-yl)-N-[(2S)-3-phenoxy-2-(triethylsilyloxy)propyl]-tert-butoxycarbonylamine (130 mg).
