Using 4-pyrazoleboronic acid pinacol ester (2.0 g, 10.31 mmol) and tert-butyl bromoacetate (2.212 g, 11.34 mmol) as the raw material, the mixture was reacted with potassium carbonate (1.709 g, 12.37 mmol) in acetone (20 mL) for 13 h at 65 °C with stirring under nitrogen protection. Upon completion of the reaction, the reaction mixture was poured into ice water (20 mL) and extracted with ethyl acetate (50 mL × 2). The organic phases were combined, washed with saturated brine, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: petroleum ether/ethyl acetate = 5/1) to afford the target compound tert-butyl 2-(4-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazol-1-yl)acetate (3 g, 8.76 mmol, 85% yield) as an oil. lC-MS (Method C): m/z 309.2 ([M+H]+), retention time: 1.946 min; 1H NMR (400 MHz, CDCl3) δ 7.82 (s, 1H), 7.75 (s, 1H), 4.82 (s, 2H), 1.47 (s, 9H), 1.28 (s, 12H).
