Benzyl 4-(2-hydroxyethoxy)piperidine-1-carboxylate (6.70 g, 24.0 mmol) produced in Reference Example 1 (1b) and 3,4-epoxytetrahydrofuran (1.03 g, 12.0 mmol) were dissolved in dichloromethane (5.0 mL). To the resulting mixture, a boron trifluoride diethyl ether complex (0.34 g, 2.4 mmol) was added at room temperature, followed by stirring for 16 hours. More boron trifluoride diethyl ether complex (0.34 g, 2.4 mmol) was added, followed by further stirring for two hours. Triethylamine (1.82 g, 18.0 mmol) was then added, and the resulting reaction liquid was directly purified by basic silica gel column chromatography (hexane:ethyl acetate, 100:0-0:100, ethyl acetate:methanol, 100:0-95:5, V/V) to give the desired title compound (2.14 g, yield 49%).
