[OH:1][C:2]1[CH:3]=[CH:4][C:5]2[S:10][C:9]([C:11]3[CH:16]=[CH:15][CH:14]=[CH:13][N:12]=3)=[N:8][C:7](=[O:17])[C:6]=2[CH:18]=1.[CH2:19](Br)[CH:20]([CH3:22])[CH3:21].C(=O)([O-])[O-].[K+].[K+].CN(C=O)C>O>[CH2:19]([O:1][C:2]1[CH:3]=[CH:4][C:5]2[S:10][C:9]([C:11]3[CH:16]=[CH:15][CH:14]=[CH:13][N:12]=3)=[N:8][C:7](=[O:17])[C:6]=2[CH:18]=1)[CH:20]([CH3:22])[CH3:21]
A mixture of 6-hydroxy-2-(2-pyridyl)-4H-1,3-benzothiazine-4-one (0.35 g, 1.3 mmol), isobutyl bromide (0.64 g, 4.6 mmol) and potassium carbonate (0.57 g, 4.1 mmol) and DMF (10 ml) was stirred at room temperature for 15 hrs. The reaction mixture was diluted with water and extracted with ethyl acetate. The extract was washed with water and dried. The solvent was evaporated. The residue was subjected to a silica gel column chromatography and eluted with hexane-ethyl acetate (2:1, v/v). The obtained crystals were recrystallized from ethyl acetate-hexane to give the titled compound (0.08 g, 19%).
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