In a 50-ml flask, 0.70 g (0.0023 mol) of 8-fluoro-4-methoxy-2,5-dimethylthiochroman-6-carboxylic acid-1,1-dioxide, 0.28 g (0.0025 mol) of 1-ethyl-5-hydroxypyrazole and 0.52 g (0. 0025 mol) of DCC (N,N'-dicyclohexylcarbodiimide) were added to 5 ml of tert-amyl alcohol at the same time, and the mixture was stirred at room temperature for 30 minutes. Then, 0.17 g (0.00125 mol) of anhydrous potassium carbonate was added. The reaction mixture was allowed to react at 80° C. for 8 hours, and then the reaction solvent was distilled off under reduced pressure. The remainder was dispersed in a 2% potassium carbonate aqueous solution and ethyl acetate to separate it into two phases. Further, the aqueous phase was acidified with 5% hydrochloric acid, and the precipitated oil was extracted with ethyl acetate. The extract was dried over anhydrous sodium sulfate and then concentrated under reduced pressure to give 0.70 g of 8-fluoro-4-methoxy-2,5-dimethyl-6-(1-ethyl-5-hydroxypyrazol-4-yl)carbonylthiochroman-1,1-dioxide (Compound 40) shown in Table 5. The yield thereof was 78%.
