The general procedure for the synthesis of 2-chloro-6-(trifluoromethyl)benzothiazole from 2-amino-6-(trifluoromethyl)benzothiazole was as follows: in a three-necked flask equipped with a condenser tube, copper chloride (370 mg, 2.75 mmol) was suspended in acetonitrile (5 mL), tert-butyl nitrite (0.41 mL, 3.44 mmol) was added, and the solution was stirred for 10 min at room temperature. Subsequently, a solution of 2-amino-6-trifluoromethylbenzothiazole (500 mg, 2.29 mmol) in acetonitrile (1 mL) was added slowly and dropwise. The reaction mixture was heated to 65 °C, maintained for 30 min and then cooled and diluted with excess 1N hydrochloric acid aqueous solution. The reaction mixture was extracted with ethyl acetate, the organic phase was separated, dried over anhydrous magnesium sulfate and concentrated under reduced pressure to give an orange semi-solid product (501 mg, 92% yield), which could be used in subsequent reactions without further purification. The product was identified by 1H NMR (300 MHz, CDCl3): δ 8.10-8.05 (m, 2H), 7.74 (d, 1H); LC-MS detection showed m/z 238.2 (MH+) with a retention time of 3.76 min; and TLC analysis showed an Rf value of 0.50 (unfolding reagent ratio of hexane/ethyl acetate 9:1).
