General procedure: preparation of ethyl 2-chloro-4-(trifluoromethyl)thiazole-5-carboxylate; ethyl 2-amino-4-(trifluoromethyl)thiazole-5-carboxylate (1.0 g, 4.16 mmol) was slowly added to CuCl2 (671 mg, 4.99 mmol) and isoamyl nitrite (732 mg, 6.24 mmol) in acetonitrile (10 ml) at 0°C in a in the mixture. The reaction mixture was stirred at room temperature for 1 hour and then heated to 50 °C to continue the reaction for 1 hour. After completion of the reaction, most of the solvent was removed under reduced pressure and the residue was poured into a mixture of ice and concentrated hydrochloric acid. The mixture was extracted with dichloromethane, the organic layer was washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by fast silica gel column chromatography (eluent: hexane/ethyl acetate = 20:1) to afford the target compound ethyl 2-chloro-4-(trifluoromethyl)thiazole-5-carboxylate (762 mg, 71% yield).1H NMR (300 MHz, DMSO-d6) δ 1.26 (t, J=7.0 Hz, 3H), 4.31 (q, J=7.0 Hz, 2H).
