[Br:1][C:2]1[C:13]([F:14])=[CH:12][C:5]2[C:6]([C:9]([OH:11])=[O:10])=[N:7][S:8][C:4]=2[CH:3]=1.OS(O)(=O)=O.[C:20]([O-])([O-])=O.[Na+].[Na+]>CO.O>[Br:1][C:2]1[C:13]([F:14])=[CH:12][C:5]2[C:6]([C:9]([O:11][CH3:20])=[O:10])=[N:7][S:8][C:4]=2[CH:3]=16-Bromo-5-fluorobenzo[d]isothiazole-3-carboxylic acid (I-25D) (57 mg, 0.21 mmol) was suspended in dry methanol (5 mL) and H2SO4 (0.2 mL) and refluxed for 3 hours. After this time the reaction was cooled to room temperature and diluted with water (3 mL) and neutralized with 5% aquesou Na2CO3 and extracted with ethyl acetate. The organic layer was washed with brine, dried over sodium sulfate and concentrated in vacuo to yield methyl 6-bromo-5-fluorobenzo[d]isothiazole-3-carboxylate (I-25E). MS 289.9 and 291.9 (M+1; Br79/Br81 isotope pattern).
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