N,N-Dimethylformamide (0.2 ml) was added to a solution of [4-(3-bromophenyl)-7-chloro-6-methyl-2-oxo-2H-chromen-3-yl]acetic acid (13.5 g) in tetrahydrofuran (135 ml), and then thionyl chloride (5.12 g) was added dropwise to the resulting mixture with passing nitrogen through the reaction vessel at 25° C. After completion of the addition, the mixture was warmed to 40° C. and stirred for 1.5 hours. Then, 2-amino-5-fluorobenzotrifluoride (6.53 g) was added thereto, and the mixture was warmed to 60° C. and then stirred for 2.5 hours. Acetonitrile (67.5 ml) and water (67.5 ml) were added dropwise successively thereto at 40 to 50° C. The resulting mixture was stirred at 40° C. for 1 hour and at 5° C. for 1 hour. Crystals precipitated was collected by filtration, and washed with cold tetrahydrofuran/acetonitrile/water (2/1/1, 40.5 ml). The resulting crystals (17.3 g) were dissolved in acetone (173 ml) by heating. Activated charcoal (0.865 g) was added to the solution, and the mixture was stirred for 10 minutes. The activated charcoal was removed by filtration, and washed with acetone (86.5 ml). The combined filtrate and washings were kept at 40° C., and water (51.9 ml) was added dropwise thereto with stirring. The mixture was cooled to 5° C. and stirred for 1 hour. Crystals were collected by filtration and washed with cold acetone/water (5/1, 51.9 ml) to obtain the title compound (16.1 g, yield 85.7%).
