The reaction was carried out with 4-pyrazoleboronic acid pinacol ester (1.7 g, 8.8 mmol) and N-(2-chloroethyl)pyrrolidine hydrochloride (1.48 g, 8.70 mmol) in the presence of potassium carbonate (3.7 g, 27.00 mmol) for 6 hours at 80 °C with stirring in DMF (15 mL). After completion of the reaction, the reaction mixture was diluted with water (50 mL) and extracted with dichloromethane (50 mL x 3). The organic layers were combined, washed with saturated aqueous sodium chloride solution (15 mL), dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by silica gel column chromatography with dichloromethane/ethyl acetate (v/v, 20/1) as eluent to afford the light yellow liquid product 1-[2-(1-pyrrolidinyl)ethyl]-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (1.27 g, 50.10% yield). Mass spectrum (ESI, positive ion mode) m/z: 292.10 [M + 1]+.
