General procedure for the synthesis of ethyl 2-bromobenzothiazole-6-carboxylate from ethyl 2-aminobenzothiazole-6-carboxylate: commercially available ethyl 2-aminobenzothiazole-6-carboxylate (10 g, 45 mmol) was dissolved in acetonitrile (40 mL), and this solution was then added to a solution containing copper(II) bromide (12 g, 54 mmol) and tert-butyl nitrite (9 mL, 75 mmol) in a solution of acetonitrile (100 mL). The reaction was carried out at room temperature and under nitrogen protection with continuous stirring for 45 min. Upon completion of the reaction, the reaction mixture was diluted with 1N HCl (300 mL) and subsequently extracted with dichloromethane (3 x 300 mL). The organic extracts were combined, washed with water (300 mL), dried with anhydrous magnesium sulfate, filtered through a silica gel plug, and finally the solvent was removed under reduced pressure to afford the target product ethyl 2-bromobenzothiazole-6-carboxylate (Step 1) as an off-white solid (11.5 g, 89% yield). The product was characterized by 1H NMR (CDCl3): δ 1.40 (t, 3H), 4.40 (q, 2H), 8.00 (d, 1H), 8.20 (d, 1H), 8.60 (s, 1H).
