To 4-pyrazoleboronic acid pinacol ester (1 g, 5.15 mmol, 1.00 eq.) and isobutyl bromide (1.05 g, 7.66 mmol, 1.49 eq.) in ethyl acetate (60 mL), Cs2CO3 (3.36 g, 10.31 mmol, 2.00 eq.) was added. The reaction mixture was stirred at 80 °C for 4 hours. After completion of the reaction, it was cooled to room temperature and filtered to remove insoluble solids. The filtrate was diluted with ethyl acetate (30 mL) and subsequently washed with brine (40 mL). The organic layer was dried over anhydrous sodium sulfate and concentrated in vacuum to afford 1-isobutyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (1.14 g, 88% yield) as a colorless oil.1H-NMR (300 MHz, CDCl3): δ 7.78 (s, 1H), 7.65 (s, 1H), and 3.91 (d, J=7.2Hz, 2H), 2.24-2.19 (m, 1H), 1.32 (s, 12H), 0.90 (d, J=7.2Hz, 6H) ppm. lcms (method D, ESI): rt=1.51min, m/z=251.0[M+H]+.
