Synthesis
General procedure for the synthesis of 5-hydroxymethylthiophene-2-boronic acid from 2-thiophene methanol: 2-hydroxymethylthiophene (2.28 g, 20 mmol) was dissolved in molecularly sieve-dried tetrahydrofuran (40 mL), the solution was cooled to -78 °C, and a 1.6 M n-butyllithium solution (25 mL, 40 mmol) in n-hexane was added slowly and dropwise, protected by argon gas. Subsequently, the reaction mixture was warmed to -30 °C and then cooled again to -78 °C and a solution of tetrahydrofuran (20 mL) of trimethyl borate (6.69 mL, 60 mmol) was added dropwise at this temperature. The reaction was held between -78 °C and -70 °C for 15 minutes. After continuing to stir at -78 °C for 2 h, the mixture was slowly warmed to room temperature and poured into water (50 mL) and the pH was adjusted to 3. 2 N aqueous hydrochloric acid (28 mL) was added and the mixture was extracted with ether, the extract was washed with saturated aqueous sodium chloride, dried over anhydrous sodium sulfate, filtered, and concentrated. The product 5-hydroxymethylthiophene-2-boronic acid 1.1 g (yield 36%) was obtained as a brown oil. Mass spectrum (MS): 158 (M).
