Synthesis
Under nitrogen protection, 2-bromo-6-fluoropyridine (2.5 g, 14.2 mmol, 1 eq.) and triisopropyl borate (4 mL) were dissolved in a solvent mixture of toluene (50 mL) and tetrahydrofuran (12.5 mL) and the reaction system was cooled to -78 °C. n-Butyllithium (10.8 mL, 1.6 M hexane solution) was slowly added dropwise over 1.25 hours. After the dropwise addition was completed, the reaction mixture was stirred at -78 °C for 30 min, followed by slow warming to 0 °C over 2 h. Upon completion of the reaction, the reaction was quenched with 2M aqueous hydrochloric acid solution (10 mL) and stirred at room temperature for 1 hour. The organic phase was separated, washed with 0.5 M aqueous hydrochloric acid, dried over anhydrous sodium sulfate and concentrated under a stream of nitrogen to remove the solvent. The aqueous phase was neutralized with saturated sodium bicarbonate solution and extracted with ethyl acetate, the organic phases were combined, dried over anhydrous sodium sulfate and concentrated under a stream of nitrogen to give the second product. Final isolation afforded 2-fluoropyridine-6-boronic acid as a white solid (1.27 g, 64% yield).
