In a three-necked reaction flask equipped with a dosing loophole, tetrahydrofuran solution was added, the stirring device was started, 4-bromo-1-propyl-1H-pyrazole and pinacol borane were added to 350mL of tetrahydrofuran, the reaction solution was cooled to -10C, 175mL of tetrahydrofuran solution of n-butyllithium was added slowly dropwise, after the dropwise, the reaction was carried out for 12 hours at room temperature. To the reaction solution was added 300 mL of aqueous ammonium chloride solution, stirred for 30 minutes, then 400 mL of ethyl acetate was added, the organic layer was separated, the organic layer was dried over anhydrous sodium sulfate, filtered, the filtrate was evaporated, and the residue was recrystallized with 20% by volume ethanol to obtain the product 1-propyl-1H-pyrazole-4-boronic acid pinacol ester.
