[NH2:1][C:2]1[CH:7]=[CH:6][C:5]([Br:8])=[CH:4][C:3]=1[SH:9].Br[CH2:11][C:12](OCC)=[O:13].C(=O)(O)[O-].[Na+]>CN(C=O)C.O>[Br:8][C:5]1[CH:6]=[CH:7][C:2]2[NH:1][C:12](=[O:13])[CH2:11][S:9][C:3]=2[CH:4]=1A mixture of 2-amino-5-bromo-benzenethiol (20 g, 0.1 mol), ethyl bromoacetate (19 g, 0.1 mol), and sodium bicarbonate (8.8 g, 0.1 mol) in DMF (200 ml) was heated to reflux for 2 hours. The mixture was diluted with water and extracted with ethyl acetate (2×100 mL). The combined organic extracts were washed with water, then brine, dried (MgSO4) and evaporated to obtain the crude 7-bromo -4H-benzo[1,4]thiazin-3-one (20 g, 82%). A small portion of sample was recrystallized from ethanol to afford pure 7-bromo-4H-benzo[1,4]thiazin-3-one: mp 212-213° C.; MS (EI) m/z 243/245 (M+).
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