Synthesis
General procedure for the synthesis of 2-chloro-5-phenyloxazole from 5-phenyloxazole: 5-phenyloxazole (1.0 g, 6.89 mmol) and anhydrous THF (10 mL) were added to a round bottom flask. The reaction system was cooled to -78 °C. At -78 °C, 2.5 M n-butyllithium (nBuLi, 3.03 mL, 7.58 mmol) was slowly added dropwise to the reaction solution, which turned dark red. After keeping the reaction at -78 °C for 15 min, hexachloroethane (1.170 mL, 10.33 mmol) was added. Subsequently, the reaction system was slowly warmed to room temperature over a period of 2 h. The reaction solution was then quenched by pouring it into ice water. The aqueous phase was extracted with ethyl acetate (EtOAc, 2 x 30 mL). The organic phases were combined, washed with saturated aqueous sodium chloride (NaCl), dried over anhydrous magnesium sulfate (MgSO4), filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (ISCO system) using 0-100% ethyl acetate/hexane gradient elution to afford the target product 2-chloro-5-phenyloxazole (600 mg, 3.34 mmol, 49% yield) as a colorless liquid. The product was analyzed by mass spectrometry (calculated value: C9H6ClNO m/z 179.1, measured value: 180.1 [M+H]+); 1H NMR (500 MHz, CDCl3) δ 7.60 (d, J=7.15 Hz, 2H), 7.43 (t, J=7.42 Hz, 2H), 7.38-7.33 (m, 1H), 7.29 (s, 1H). 1H); 13C NMR (126 MHz, CDCl3) δ 153.78, 146.16, 129.01, 126.93, 124.03, 123.31.
References
[1] Organic Letters, 2005, vol. 7, # 15, p. 3351 - 3354
[2] Patent: WO2018/64119, 2018, A1. Location in patent: Paragraph 0819
[3] Patent: WO2013/12827, 2013, A1. Location in patent: Paragraph 00208
[4] Journal of Organic Chemistry, 1996, vol. 61, # 16, p. 5192 - 5193
