The general procedure for the synthesis of 5-amino-4-bromobenzothiazole from 1,3-benzothiazol-5-amine is as follows: a solution of bromine (2.3 g, 14.4 mmol) in trichloromethane (10 mL) was slowly added dropwise to a solution of benzo[d]thiazol-5-amine (2.1 g, 14.0 mmol) in trichloromethane (100 mL) at 10 °C. The reaction mixture was stirred continuously for 1 hour at room temperature. Subsequently, the reaction mixture was alkalized with saturated aqueous sodium carbonate solution (100 mL) and extracted with dichloromethane (3 x 30 mL). After combining the organic layers, they were dried with anhydrous sodium sulfate and concentrated under vacuum. The residue was purified by silica gel column chromatography (eluent ratio ethyl acetate/petroleum ether = 1:4) to give a final yellow solid 5-amino-4-bromobenzothiazole (2.3 g). The product was characterized by 1H NMR (300 MHz, CDCl3): δ 9.01 (s, 1H), 7.66 (d, 1H), 6.95 (d, 1H), 4.33 (s, 2H).
