A solution of the compound (526 mg, 1.0 mmol) obtained in Example 25-3), phenylboronic acid (244 mg, 2.0 mmol), tetrakis(triphenylphosphine)palladium(0) (231 mg, 0.2 mmol), and potassium carbonate (276 mg, 2.0 mmol) in dimethoxyethane (4 mL) and water (1 mL) was stirred at 100° C. for 3.5 h. The reaction mixture was cooled to room temperature, saturated aqueous sodium hydrogencarbonate was added to the reaction mixture, the mixture was extracted with dichloromethane, and the organic layer was washed with saturated sodium chloride solution and dried with anhydrous sodium sulfate. After filtration, the filtrate was concentrated under reduced pressure, and the residue was partially purified by silica gel chromatography (Isco Combiflash, 40 g, methanol:ethyl acetate=0:100 to 40:60, gradient). A solution of this partially purified product and 4 M hydrochloric acid (1,4-dioxane solution, 2 mL) in methanol (2 mL) was stirred at room temperature for 14 h. The reaction mixture was concentrated under reduced pressure, saturated aqueous sodium hydrogencarbonate was added to the residue, the mixture was extracted with dichloromethane, and the organic layer was washed with saturated sodium chloride solution and dried with anhydrous sodium sulfate. After filtration, the filtrate was concentrated under reduced pressure, and the residue was purified by silica gel chromatography (Isco Combiflash, 12 g, methanol:ethyl acetate=0:100 to 40:60, gradient) to obtain the title compound (138 mg, 34%) as a colorless solid.
