Synthesis
Step 2: Ethyl 2-amino-4-(trifluoromethyl)oxazole-5-carboxylate (A-1) (9.8 g) was suspended in acetonitrile (100 mL), and copper (II) bromide (11.8 g) and tert-butylnitrite (13.8 mL) were slowly added sequentially at 0 °C. The reaction mixture was slowly warmed from 0 °C to room temperature under nitrogen protection and stirred at this temperature for 4 hours. Upon completion of the reaction, the mixture was concentrated. The concentrated residue was suspended in EtOAc (200 mL), washed sequentially with 1N HCl (3 x 100 mL) and brine (1 x 100 mL), and the organic phase was dried over Na2SO4, filtered and concentrated. The crude product was purified by fast column chromatography (eluent: EtOAc/hexane) to afford ethyl 2-bromo-4-trifluoromethyl oxazole-5-carboxylate (A-2) as a colorless liquid (9.18 g, 73% yield).LCMS (ESI) [M + 1]+ 288.2.
References
[1] Patent: WO2010/59606, 2010, A2. Location in patent: Page/Page column 159
[2] Patent: WO2018/11628, 2018, A1. Location in patent: Paragraph 00321
[3] Bioorganic and Medicinal Chemistry Letters, 2013, vol. 23, # 23, p. 6410 - 6414
