1-Oxo-1,3-dihydroisobenzofuran-6-carbonitrile (3.01 g, 18.9 mmol) obtained from Example 5-(2) was dissolved in a mixed solvent (200 ml) of tetrahydrofuran-methanol (3:1), and an aqueous solution of sodium hydroxide (1.004N; 17.4 ml, 17.4 mmol) was added thereto over a period of 10 minutes. The mixture was stirred at room temperature for 30 minutes, and the solvent was distilled off under reduced pressure. The resulting residue was dried using a vacuum pump. The obtained solid was dissolved in N,N-dimethylformamide (40 ml), and 4-methoxybenzyl chloride (2.96 g, 18.9 mmol) was added thereto. The mixture was heated at 70-80° C. for 1 hour. After cooling the mixture to 0° C., dichloromethane (40 ml) was added thereto, and 4-(N,N-dimethylamino)pyridine (5.78 g, 47.3 mmol) and allyl chloroformate (4.56 g, 37.9 mmol) were added thereto, then the mixture was stirred at the same temperature for 30 minutes. The mixture was diluted with ethyl acetate and then washed successively with water and an aqueous solution of sodium chloride. The resulting mixture was dried over anhydrous magnesium sulfate, and the solvent was distilled off under reduced pressure to give an oily residue. The residue was subjected to chromatography on a silica gel (100 g) column (eluent; hexane:ethyl acetate=3:1) to afford the title compound (3.11 g, 43% yield) as a colorless oil.
