The compound (4.0 g, 10.46 mmol) synthesized in Example 2 (2a) was dissolved in pyridine (30 mL) and benzoyl chloride (12.1 mL, 104.24 mmol) was added thereto under ice-cooling, followed by stirring of the mixture at room temperature for 14 hours. The reaction mixture was poured to 10% aqueous hydrochloric acid solution (20 mL) and methyl chloride (20 mL) and the organic layer was washed with 10% aqueous hydrochloric acid solution (20 mL), saturated aqueous sodium hydrogencarbonate solution (20 mL) and saturated brine (20 mL) and dried with anhydrous sodium sulfate, followed by distilling off of the solvent under reduced pressure. The residue was purified using silica gel flash column chromatography (hexane:ethyl acetate, 5:1-5:2, V/V) to obtain the desired title compound (8.10 g, yield 70%) as a colorless oil.
