According to the method of Example 103, Step A, a mixture of Intermediate 90 (121 mg), tert-butyl 4-oxo-1-piperidinecarboxylate (274 mg), titanium tetraisopropoxide (0.41 ml) and dichloromethane (7 ml) was stirred at room temperature for 138 hours. The reaction mixture was added with sodium borohydride (114 mg) and methanol (1 ml) and stirred for 1.5 hours with ice cooling. The reaction mixture was added with saturated aqueous sodium hydrogencarbonate (10 ml) with ice cooling and extracted twice with ethyl acetate (15 ml for each time). The organic layer was dried over anhydrous sodium sulfate, and then the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (n-hexane:ethyl acetate=1:1) to obtain the title compound (53.5 mg).
