Under nitrogen protection, 2,3-dibromothiophene (12.1 g, 0.025 mol) was dissolved in anhydrous ether (15 mL) and cooled to -78°C. A solution of n-butyllithium (2.5 M, 22 mL, 0.055 mol) in ether was slowly added dropwise. After the dropwise addition, stirring was continued at -78 °C for 10 minutes. Subsequently, gaseous carbon dioxide was passed into the reaction system and a white precipitate was immediately observed to form. After keeping the reaction at -78 °C for 30 min, the reaction was slowly warmed up to room temperature. Upon completion of the reaction, the reaction was quenched with Milli-Q water and the aqueous phase was extracted with 10% sodium hydroxide solution (3 x 50 mL). The aqueous phase was combined, acidified with 6 N hydrochloric acid and the precipitate precipitated was collected by filtration. The resulting solid was recrystallized with ethanol (50 mL) and water (200 mL) and dried in vacuum to give the white powdery product 3-bromothiophene-2-carboxylic acid (9.23 g). The product was analyzed by 19F NMR, mass spectrometry (70 eV, EI): m/z 208 (M-1), 1H NMR (CDCl3): δ 7.81 (d, 1H, J=5.2 Hz), 7.19 (d, 1H, J=5.2 Hz) and 13C NMR (CDCl3): δ 117.6, 133.8, 134.6, 162.6, 207.6 Confirmed structure.
