The 7-iodo-3-(2-trifluoromethylphenyl)-2H-isoquinolin-1-one (20.8 mg, 0.05 mmol) prepared in step D of Example 1-1, tris(dibenzylideneacetone)dipalladium (2.2 mg, 0.0025 mmol), 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (4.2 mg, 0.0075 mmol), cesium carbonate (22.8 mg, 0.07 mmol), and 2-pyrrolidone (4.6 μl) were suspended in 1,4-dixane (0.5 ml), and the suspension was then stirred under heating to reflux overnight. Thereafter, the reaction solution was cooled to a room temperature, and a saturated ammonium chloride aqueous solution was then added thereto, followed by extraction with ethyl acetate. The extract was dried over anhydrous sodium sulfate, and the solvent was then distilled away under reduced pressure. The obtained residue was purified by silica gel column chromatography (ethyl acetate hexane=2:1 to 5:1), so as to obtain 7-(2-oxopyrrolidin-1-yl)-3-(2-trifluoromethylphenyl)-2H-isoquinolin-1-one (15.3 mg; yield: 82%) in the form of a colorless solid.
