A solution of the compound (800 mg, 1.57 mmol) obtained in Example 52-1), oxazole (217 mg, 3.15 mmol), tetrakis(triphenylphosphine)palladium(0) (91 mg, 0.08 mmol), and lithium tert-butoxide (260 mg, 3.15 mmol) in dioxane (12 mL) was stirred for 2 h with heating to reflux. The reaction mixture was cooled to room temperature, saturated aqueous ammonium chloride (50 mL) was added to the reaction mixture, the mixture was extracted with ethyl acetate, and the organic layer was washed with saturated sodium chloride solution and dried with anhydrous sodium sulfate. After concentration under reduced pressure, the residue was purified by silica gel chromatography (ethyl acetate:methanol=70:30) to obtain the title compound (674 mg, 86%) in a yellow oily form.
