[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([N:8]2[C:13](=[O:14])[NH:12][C:11]3[CH:15]=[C:16]([O:19][CH3:20])[CH:17]=[CH:18][C:10]=3[S:9]2(=[O:22])=[O:21])=[CH:4][CH:3]=1.[H-].[Na+].[CH3:25]I>CN(C)C=O>[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([N:8]2[C:13](=[O:14])[N:12]([CH3:25])[C:11]3[CH:15]=[C:16]([O:19][CH3:20])[CH:17]=[CH:18][C:10]=3[S:9]2(=[O:21])=[O:22])=[CH:4][CH:3]=1To a solution of 2-(4-chlorophenyl)-6-methoxy-2H-1,2,4-benzothiadiazine-3(4H)-one 1,1-dioxide (23.50 g) in dried N,N-dimethylformamide (150 ml) was added sodium hydride (60% oil dispersion) in one portion at 0° C. The suspension was stirred for one hour at ambient temperature and then methyl iodide (5.18 ml) was added therein at the same temperature. The reaction mixture was stirred for one and half hours a ambient temperature and then poured into ice water. The separated solid was filtered, dried and recrystrallized from ethanol to yield 2-(4-chlorophenyl)-6-methoxy-4-methyl-2H-1,2,4-benzothiadiazine-3(4H)-one 1,1-dioxide (21.07 g) as a white needle crystal.
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