To a solution of N,N-dimethylformamide (DMF, 52 mL) of pinacol ester of 4-pyrazoleboronic acid (5.0 g, 25.8 mmol) was added cesium carbonate (Cs2CO3, 8.396 g, 25.8 mmol) and methyl bromoacetate (2.52 mL, 25.8 mmol). The reaction mixture was stirred at 90 °C under nitrogen protection overnight. After completion of the reaction, the mixture was cooled to room temperature, diluted with water and extracted with ethyl acetate. The organic phases were combined, washed sequentially with water three times, brine once and dried over anhydrous sodium sulfate (Na2SO4). The organic phase was concentrated under reduced pressure to afford methyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole-1-acetate (4.27 g, 62% yield).
