CS([O:5][CH2:6][CH2:7][CH2:8][CH2:9][C:10]([CH3:14])=[C:11]([F:13])[F:12])(=O)=O.[N:15]1[S:19][N:18]=[C:17]2[CH:20]=[C:21]([C:24](O)=[O:25])[CH:22]=[CH:23][C:16]=12.C(=O)([O-])O.[Na+]>CN(C)C=O.O>[N:15]1[S:19][N:18]=[C:17]2[CH:20]=[C:21]([C:24]([O:5][CH2:6][CH2:7][CH2:8][CH2:9][C:10]([CH3:14])=[C:11]([F:13])[F:12])=[O:25])[CH:22]=[CH:23][C:16]=12To 30 ml of ethanol was dissolved 2.0 g (10 mmol) of methyl benzo[1,2,5]thiadiazole-5-carboxylate, followed by the addition of 3.3 g of a 25% aqueous solution of sodium hydroxide and stirring at room temperature for 3 hours. To the reaction liquid was added 50 ml of water and a dilute hydrochloric acid to make pH of 2. Crystal precipitated was filtered off and dried under reduced pressure to obtain 1.7 g (yield: 92%) of benzo[1,2, 5]thiadiazole-5-carboxylic acid. In a separate reactor, 0.50 g (2.2 mmol) of 6,6-difluoro-5-methyl-5-hexenyl methanesulfonate and 0.43 g (2.4 mmol) of benzo[1,2,5]thiadiazole-5-carboxylic acid were dissolved in 7 ml of N,N-dimethylformamide, followed by the addition of 0.37 g (4.4 mmol) of sodium hydrogencarbonate and stirring at 100° C. for 3 hours. The reaction liquid was then poured in water and extracted with ethyl acetate. The organic layer was washed with water and a saturated saline solution in this order, followed by drying over anhydrous magnesium sulfate and concentration under reduced pressure. The residue was purified with silica gel column chromatography (ethyl acetate:hexane=1:19) to obtain 0.44 g (yield: 64%) of 6,6-difluoro-5-methyl-5-hexenyl benzo[1,2,5]thiadiazole-5-carboxylate.
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