Trimethyl borate → 1-Methyl-3-(trifluoroMethyl)pyrazole-5-boronic acid

To a stirred solution of 1-methyl-3-(trifluoromethyl)-1H-pyrazole (1.89 g, 12.6 mmol) in anhydrous tetrahydrofuran (20 mL) under nitrogen cooled to −78° C. was added n-butyllithium (8.3 mL, 1.6 M solution in hexanes, 13.2 mmol) slowly over 5 minutes. The resulting yellow solution was stirred at −78° C. for 1 hour and trimethyl borate (1.56 mL, 13.9 mmol) was then added slowly. The reaction flask was covered in foil and allowed to warm to room temperature for 16 hours. The white solution was quenched with aqueous 1 M hydrogen chloride solution (10 mL) and stirred at room temperature for 1.5 hours. The mixture was extracted with ethyl acetate (2×30 mL), dried with anhydrous magnesium sulphate and evaporated in vacuo to give an off-white foam (2.11 g). The foam was triturated with dichloromethane, filtered and dried in vacuo to afford the title compound as a white solid (1.57 g, 64%).