1-(4-Bromophenyl)-4-ethylpiperazine (3 g, 11 mmol) and pinacolborane were dissolved in dioxane (100 mL) and then 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (1.8 g, 12 mmol), dichlorobis(triphenylphosphine)palladium(II) (0.392 g, 0.57 mmol) and triethylamine (4.65 g, 33 mmol). The reaction mixture was heated to reflux for 12 hours. After completion of the reaction, the mixture was poured into water and extracted with dichloromethane. The organic phase was dried with anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by silica gel column chromatography with dichloromethane/methanol (9/1, v/v) as eluent. 4-(4-Ethyl-1-piperazinyl)phenylboronic acid pinacol ester was obtained as a brown oil, which crystallized on standing (2 g, yield 55.48%), melting point 130-134°C.
