4-Chlorophenyl boronic acid (1.08 g, 6.97 mmol) and 3-methoxycarbonylmethyl-piperazine-1-carboxylic acid tert-butyl ester (0.9 g, 3.48 mmol) were dissolved in dichloromethane. To this mixture was added copper acetate (0.63 g, 3.48 mmol), 4 Å molecular sieves and pyridine (0.56 mL, 6.97 mmol) and the reaction mixture was stirred at room temperature for 72 h. The reaction mixture was concentrated in vacuo and dissolved in ethyl acetate, filtered through celite and concentrated. The crude product was purified using gradient elution from hexane/ethyl acetate (5%) to hexane/ethyl acetate (20%). ESI-MS m/z: 369 (M+1), UV retention time: 2.97 min.
