1: 85 mg / boron trichloride / CH2Cl2 / 1) o-5 deg C, 3 h; 2) 5 deg C --> room temperature, 1 h 2: potassium carbonate / acetone / 1 h / Heating 3: potassium t-butoxide / dimethylsulfoxide / 6 h / 100 - 105 °C View Scheme