4-Bromothiophene-2-carboxylic acid (3.0 g, 14.5 mmol) was used as starting material and dissolved in 36 mL of anhydrous tert-butanol. Subsequently, diphenylphosphoryl azide (DPPA, 4.06 mL, 18.8 mmol) and triethylamine (Et3N, 4.04 mL, 29.0 mmol) were added sequentially to the solution. The reaction mixture was stirred at 100 °C for 5 h. The reaction process was monitored by high performance liquid chromatography (HPLC). After completion of the reaction, the solvent was removed by distillation under reduced pressure to give the crude product. The crude product was purified by Combiflash silica gel column chromatography with the eluent being a hexane solution of 0-5% ethyl acetate, resulting in 3.10 g (77% yield) of tert-butyl (4-bromothiophen-2-yl)carbamate as a white solid. The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ= 7.04 (br.s, 1H), 6.73 (dd, J = 1.8 Hz, 0.4 Hz, 1H), 6.44 (d, J = 1.8 Hz, 1H), 1.52 (s, 9H).
