Ethyl 2-amino-1,3,4-thiadiazole-5-carboxylate (21 g, 121.38 mmol) was used as starting material, which was dissolved in acetonitrile (400 mL), copper (II) bromide (53.3 g, 239.01 mmol) was added with stirring, and stirred at room temperature for 15 min. Subsequently, tert-butyl nitrite (24.65 g, 239.04 mmol) was slowly added dropwise over 20 minutes. After the dropwise addition, the reaction mixture was continued to be stirred at room temperature for 30 min and then warmed up to 60 °C for 30 min. The reaction process was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the mixture was diluted with water, extracted with ethyl acetate and filtered through a bed of diatomaceous earth. The organic layer was separated, washed with saturated brine, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford the target product ethyl 5-bromo-1,3,4-thiadiazole-2-carboxylate (25 g, 87.40% yield) as a yellow solid.TLC conditions: 20% ethyl acetate/hexane (Rf value: 0.7).1H NMR (400 MHz, DMSO-d6) data: δ 4.45-4.40 (m, 2H), 1.34 (t, J=6.8Hz, 3H).
