To a stirred solution of ethyl {cis-5-[(tert-butoxycarbonyl)amino]piperidin-2-yl}acetate (2.25 g, 7.86 mmol, step 5 of Example 1), N,N-diisopropylethylamine (1.12 g, 8.64 mmol) in acetonitrile (45 mL) was added benzyl bromide (1.48 g, 8.64 mmol) at room temperature. After stirring at room temperature for 28 h, the mixture was concentrated under reduced pressure. The resulting residue was dissolved in ethyl acetate (250 mL). The organic solution was washed with water (100 mL×3), brine (50 mL), dried over magnesium sulfate, and concentrated under reduced pressure. The resulting residue was chromatographed on a column of silica gel eluting with n-hexane/ethyl acetate (4:1) to give 2.44 g (82%) of the title compound as a colorless oil.
