Typical procedure: Under an air atmosphere, a Schlenk tube is charged with Cu(OAc)2·H2O (4.0 mg, 0.02 mmol), dppf (16.6 mg, 0.03 mmol), arylboronic acid (0.4 mmol), aldehyde (0.2 mmol), NaOAc (49.2 mg, 0.6 mmol), and toluene (3 mL) under ice-salt (-20 °C). The mixture is stirred for 0.5 h at room temperature, refluxed for 24 h, and then cooled in a Schlenk tube to room temperature. The mixture is extracted with ethyl acetate (4×5 mL), and the organic layers are washed with water. The organic layers are dried over MgSO4, concentrated, and purified by flash column chromatography on silica gel to give the desired product.