To a solution of 10 (2.56 g; 7.74 mmol) in CH2Cl2 (75 ml), CBr4 (3.63 g; 10.83 mmol) and triphenylphosphine (2.47 g; 9.31 mmol) were added respectively at 0° C. and the reaction was stirred at room temperature for 40 min. Cooled to 0° C., ethyl acetate (100 mL) and saturated aqueous NaHCO3 (30 mL) were added. The organic layer was separated and washed by saturated aqueous NaCl, and dried over anhydrous Na2SO4. After evaporation of the solvent, the residue was purified by flash column chromatography over silica gel using CH2Cl2-hexane (1:5) as the eluent to afford 11 as white solid (3.02 g; 92% yield): 1H NMR (400 MHz, CDCl3) δ 7.42-7.48 (m, 6H, six of ArH), 7.27-7.33 (m, 6H, six of ArH), 7.20-7.27 (m, 3H, three of ArH), 5.37 (s, 1H, one of C═CH2), 5.31 (s, 1H, one of C═CH2), 4.01 (s, 2H, CH2Br), 3.75 (s, 2H, Ph3COCH2); 13C NMR (100 MHz, CDCl3) δ 143.6, 142.6, 128.4, 127.6, 126.9, 115.8, 86.9, 64.2, 33.5, (9).
