Under nitrogen protection, 3-bromo-5-(trifluoromethyl)pyridine (2.5 g, 11.06 mmol) and triisopropyl borate (3.06 mL, 13.27 mmol) were dissolved in anhydrous tetrahydrofuran (20 mL) and cooled to -78 °C. A hexane solution of n-butyllithium (2.5 M, 4.9 mL, 12.17 mmol) was slowly added dropwise, keeping the reaction mixture stirred at -78 °C for 3 hours. Subsequently, the reaction mixture was slowly warmed to -10 °C. The reaction was quenched by addition of water (20 mL) and the tetrahydrofuran was removed by distillation under reduced pressure. The remaining aqueous phase was diluted with water (40 mL) and washed with ether (2 x 40 mL). The aqueous phase was adjusted to pH 5 with acetic acid and the resulting suspension was extracted with ethyl acetate (80 mL). The organic phase was separated, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to give 3-(trifluoromethyl)pyridine-5-boronic acid as a brown solid (2.022 g, 96% yield). HPLC/MS analysis: retention time 1.47 min, mass-to-charge ratio 192.1 (M+H+).
