General procedure for the synthesis of 2-bromo-5-phenyl-1,3,4-oxadiazole from 2-phenyl-1,3,4-oxadiazole: To a 500 mL four-necked flask was added tetrahydrofuran (170 mL) and 2-phenyl-1,3,4-oxadiazole (17.0 g, 0.1163 mol). The reaction mixture was cooled to -65 to -70 °C under nitrogen protection and n-butyllithium (60.66 mL, 2.3 M in hexane, 0.1395 mol) was added dropwise over a period of 1 h. The reaction was stirred for 1.0 h at the same temperature. Subsequently, bromine (11.15 g, 0.1395 mol) was added slowly at -65 to -70 °C. The reaction was continued to be stirred at the same temperature for 1.0 h. The progress of the reaction was monitored by TLC. After completion of the reaction, the mixture was slowly warmed to -10 °C and the reaction was quenched with 1.0 N HCl solution (100 mL). The mixture was further warmed to room temperature and extracted with ethyl acetate (2 x 100 mL). The organic layers were combined, washed sequentially with water (100 mL) and brine (100 mL), dried over anhydrous sodium sulfate, and concentrated to a volume under reduced pressure. Crystallization by petroleum ether gave 2-bromo-5-phenyl-1,3,4-oxadiazole as a white solid (yield: 24.3 g, 93%). 1H-NMR (400 MHz, DMSO-d6): δ 7.57-7.68 (m, 3H), 7.95-7.98 (m, 2H). MS (ESI) m/z: 226.0.
