2,4-Difluorophenylacetonitrile → 3-(2,4-difluorophenyl)-6-trifluoromethyl-2H-pyran-2-one

7.7 g (69 mmol) of potassium tert-butoxide was dissolved in 200 ml of THF, and 10 g (65 mmol) of 2,4-difluorophenyl acetonitrile was dropwise added thereto under cooling with ice. Ten minutes later, 13.5 g (69 immol) of (E)-4-ethoxy-1,1,1-trifluoro-3-buten-2-one was dropwise added thereto, followed by stirring at room temperature for 4 hours. THF was distilled off under reduced pressure. Then, the obtained residue was poured into water, acidified to pH 1 with 1N hydrochloric acid and then extracted with ethyl acetate. After washing with water and an aqueous sodium hydrogencarbonate solution, the organic layer was dried over anhydrous magnesium sulfate. And then, the ethyl acetate was distilled off under reduced pressure. To the obtained residue, 150 ml of concentrated hydrochloric acid was added, followed by stirring for 4 hours under heating and refluxing. This reaction solution was poured into ice water and extracted with ethyl acetate, followed by washing with water. The organic layer was dried over anhydrous magnesium sulfate, and then, ethyl acetate was distilled off under reduced pressure. The obtained residue was purified by silica gel column chromatography to obtain 13.8 g (yield: 76%) of the desired product. Melting point: 98-100° C. 1H-NMR (400 MHz, CDCl3) δ value: 6.78(1H,d), 6.95(2H,m), 7.52(1H,d), 7.56(1H,q)ppm.