Synthesis
(Step 1) Synthesis of 2-bromo-6-chlorobenzothiazole: Copper(I) bromide (1.40 g, 9.76 mmol) was suspended in acetonitrile (25 ml). To this suspension tert-butyl nitrite (1.45 ml, 12.2 mmol) was added dropwise, followed by stirring the reaction mixture at 60 °C for 15 min. Next, 2-amino-6-chlorobenzothiazole (1.50 g, 8.12 mmol) was added to the reaction system and stirring was continued at 60°C for 30 minutes. After completion of the reaction, the mixture was cooled to room temperature and diluted with ethyl acetate. The resulting organic phase was washed sequentially with 1N hydrochloric acid and saturated brine and dried over anhydrous sodium sulfate. After the solvent was removed by distillation under reduced pressure, the residue was purified by silica gel column chromatography using hexane/ethyl acetate (7:1, v/v) as eluent to afford 2-bromo-6-chlorobenzothiazole (1.39 g, 69% yield) as a yellow solid.1H-NMR (CDCl3) δ: 7.42-7.46 (m, 1H), 7.76-7.90 (m, 2H).
