4-Bromo-1,3-dimethyl-1H-pyrazole (5.00 g, 28.60 mmol) and pinacol ester of bisboronic acid (8.71 g, 34.32 mmol) were reacted in anhydrous 1,4-dioxane (100.0 mL). Potassium acetate (5.63 g, 57.41 mmol) and Pd(dppf)Cl2-CH2Cl2 (2.38 g, 2.86 mmol) were added to the reaction system. The reaction mixture was displaced three times with nitrogen to remove air, followed by warming to 100 °C and stirring the reaction overnight. After completion of the reaction, the reaction mixture was concentrated under reduced pressure. The concentrated residue was diluted with water (30 mL) and extracted with ethyl acetate (50 mL x 3). The organic layers were combined and dried over anhydrous sodium sulfate. The obtained residue was purified by silica gel column chromatography (eluent: ethyl acetate/petroleum ether) to afford the target product 1,3-dimethylpyrazole-4-boronic acid pinacol ester as a brown viscous liquid (3.80 g, 60% yield).
