A mixture of 4-bromo-2,2-bis(fluoromethyl)-6-trifluoromethyl-2H-1-benzopyran (1.72 g), potassium acetate (2.00 g), potassium iodide (0.85 g), triphenylphosphine (27 mg), palladium acetate (11 mg) and N,N-dimethylacetamide (10 ml) was stirred under a CO atmosphere at 120° C. for 9 hours. To the reaction mixture, 2 N HCl was added and the precipitating crystals were recovered by filtration. To the recovered crystals, ethyl acetate was added and the insoluble matter was filtered off; the filtrate was washed with a saturated aqueous solution of sodium thiosulfate and a saturated aqueous solution of sodium chloride, dried with anhydrous sodium sulfate and concentrated under reduced pressure; the resulting residue was dissolved in a saturated aqueous solution of sodium hydrogencarbonate and washed with dichloromethane; to the resulting aqueous layer, concentrated HCl was added to render it acidic and the precipitating crystals were recovered by filtration. The recovered crystals were dissolved in ethyl acetate, dried with anhydrous magnesium sulfate and concentrated under reduced pressure; the resulting residue was recrystallized with an ethyl acetate/hexane mixed solvent to give 2,2-bis(fluoromethyl)-6-trifluoromethyl-2H-1-benzopyran-4-carboxylic acid (1.25 g) having a melting point of 162-163° C.
