To a solution of 2,5-dibromothiophene (2.0 g, 8.3 mmol) in anhydrous THF (40 mL) was slowly added n-butyllithium (n-BuLi, 15 mL, 1.6 M hexanes solution, 25 mmol) dropwise at -78 °C and the reaction mixture was stirred for 1 hour keeping the temperature at -78 °C. Subsequently, tributyl borate (6.4 mL, 25 mmol) was added to the reaction mixture at the same temperature and the reaction system was gradually warmed to room temperature. After continued stirring for 2 hours, pinacol (3.8 g, 33 mmol) and acetic acid (1.4 mL, 25 mmol) were added sequentially and the resulting mixture was stirred and reacted for 14 hours at room temperature. After completion of the reaction, the reaction solution was filtered through a diatomaceous earth pad and the filtrate was concentrated under reduced pressure. The residue (brown solid) was purified by recrystallization from a solvent mixture of ethyl acetate and hexane to afford the target product dipinacol ester of thiophene-2,5-diboronic acid (2.0 g, 75% yield) as a white solid.
