2-Thiopheneboronic acid

1003-09-4

6165-68-0

General procedure for the synthesis of 2-thiophene boronic acid from 2-bromothiophene: Triphenylphosphine (0.131 g, 0.5 mmol, 20 mol%), p-iodoanisole (0.585 g, 2.5 mmol), and triethylamine (1.78 mL, 12.5 mmol) were added sequentially to a 50 mL round-bottomed flask (equipped with a side arm, condenser, and stirring bar). The reaction system was degassed three times by alternating vacuum and argon displacement. Palladium dichloride (0.023 g, 0.13 mmol, 5 mol%) was added under positive argon pressure. After stirring at room temperature for 15 minutes, diisopropylaminoborane (5 mL, 1 M THF solution, 5 mmol) was added and again degassed three times by alternating vacuum and argon displacement. The reaction mixture was heated to reflux and kept at reflux for 12 hours. Upon completion of the reaction, the mixture was cooled to 0°C and 6 mL of methanol was slowly added (note: this process is exothermic and accompanied by hydrogen release). After stirring for 15 minutes, all solvent was removed by distillation under reduced pressure to give a black solid. The solid was dissolved with 3M sodium hydroxide solution (8 mL) and subsequently washed with hexane (3 x 10 mL). The aqueous layer was cooled to 0°C (ice bath) and acidified with concentrated hydrochloric acid to pH ≤ 1, at which point 2-thiopheneboronic acid precipitated as a white solid. The aqueous layer was extracted with ether (3 x 10 mL), the organic phases were combined, dried with magnesium sulfate and filtered. Finally, the solvent was removed by distillation under reduced pressure to obtain 2-thiopheneboronic acid as a white solid.