The yellow oil obtained in Example 50 was dissolved in 1,2-dichloroethane (20 mL), sodium triacetoxyborohydride (1.26 g, 6.0 mmol) was added at room temperature by small portions, and the mixture was stirred at room temperature for 60 hr. Propionaldehyde (200 mg, 3.0 mmol) was added to the reaction mixture at room temperature, and the mixture was stirred at room temperature for 3 hr. The reaction mixture was poured into 10% aqueous sodium hydrogencarbonate solution, and the mixture was extracted with ethyl acetate. The ethyl acetate layer was dried using a Presep Dehydration tube (manufactured by Wako Pure Chemical Industries, Ltd.), and concentrated. The residue was purified by silica gel column chromatography (5%-70% ethyl acetate/hexane) to give the title compound (549 mg, yield 80%, 2 steps) as a yellow oil.
