General procedure for the synthesis of 2-bromo-4-(trifluoromethyl)thiazole from 2-amino-4-(trifluoromethyl)thiazole: 2-amino-4-(trifluoromethyl)thiazole (500 mg, purchased from Wako Pure Chemical Industries, Ltd.) was dissolved in a 48% aqueous hydrogen bromide solution (6 mL), and sodium nitrite (266) was added slowly and dropwise, under the cooling of an ice bath. mg) in aqueous sodium nitrite (1 mL) was slowly added dropwise under cooling in an ice bath. The reaction mixture was stirred at 0°C for 1 hour. Subsequently, the reaction was quenched by the addition of aqueous sodium bisulfite, then the pH was adjusted with aqueous sodium hydroxide and finally extracted with ether. The organic layers were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The resulting crude product was purified by silica gel column chromatography with ethyl acetate-hexane (1:9, v/v) as eluent to give 2-bromo-4-(trifluoromethyl)thiazole (167 mg, 24% yield).1H-NMR (300 MHz, DMSO-d6) δ: 8.55 (s, 1H). Referring to the operation of Example 17 of the starting material synthesis, 1-[4-(trifluoromethyl)-1,3-thiazol-2-yl]piperazine hydrochloride (194 mg, 53% yield) was prepared by the reaction of 2-bromo-4-(trifluoromethyl)thiazole (309 mg) with 1-(tert-butoxycarbonyl)piperazine (300 mg).1H-NMR (300 MHz, DMSO-d6) δ: 3.19-3.24 (m, 4H), 3.66-3.75 (m, 4H), 7.68 (s, 1H), 9.57 (brs, 2H).
