[NH2:1][C:2]1[CH:7]=[CH:6][C:5]([Br:8])=[CH:4][C:3]=1[SH:9].C(=O)([O-])[O-].[Cs+].[Cs+].Br[CH:17]([CH2:21][CH3:22])[C:18](Br)=[O:19]>CN(C=O)C>[Br:8][C:5]1[CH:6]=[CH:7][C:2]2[NH:1][C:18](=[O:19])[CH:17]([CH2:21][CH3:22])[S:9][C:3]=2[CH:4]=1To a mixture of 2-amino-5-bromo-benzenethiol (20 g, 0.1 mol) and cesium carbonate (33 g, 0.1 mol) in DMF (500 ml) at −35° C. was added dropwise 2-bromobutyrylbromide (23 g, 0.1 mol). The mixture was allowed to warm to room temperature, poured into ice/water, and extracted with CH2Cl2 (2×50 mL). The combined organic extracts were washed with water, then brine, dried (MgSO4) and evaporated. The residue was purified by column chromatography (SiO2, ethyl acetate:hexane/1:6) to afford 7-bromo-2-ethyl-4H-benzo[1,4]thiazin-3-one (3.7 g, 14%): mp 100° C.; MS (EI) m/z 271/273 (M+).
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