[Cl:1][C:2]1[CH:15]=[CH:14][C:5]2[NH:6][C:7]([S:12][CH3:13])=[N:8][S:9](=[O:11])(=[O:10])[C:4]=2[CH:3]=1.[C:16](=O)([O-])[O-].[K+].[K+].CI>C(#N)C.CO>[Cl:1][C:2]1[CH:15]=[CH:14][C:5]2[N:6]([CH3:16])[C:7]([S:12][CH3:13])=[N:8][S:9](=[O:11])(=[O:10])[C:4]=2[CH:3]=1A solution of 7-chloro-3-methylsulfanyl-4H-1,2,4-benzothiadiazine 1,1-dioxide (0.8 g) in acetonitrile (24 mL) and methanol (0.5 mL) was supplemented with potassium carbonate (0.96 g), then with methyl iodide (3 mL), and stirred at room temperature for 10 h. The solvent was removed by distillation under reduced pressure. The residue was suspended in water (40 mL) and the pH was adjusted to pH 2 with formic acid. The precipitate of the title compound was collected by filtration, washed with water and dried. The compound was used without further purification in the next step (yield: 0.53 g).
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