A 100 ml heavy wall round bottom flask was charged with the crude intermediate 4-trifluoromethanesulfonyloxy-cyclohex-3-ene-1,1-dicarboxylic acid diethyl ester (4.0 g, 80% purity, 8.55 mmol, 1.0 equiv) from last step, PdCl2(dppf)-CH2Cl2 adduct (0.628 g, 0.769 mmol, 0.09 equiv), 4-chloro-phenylboric acid (2.67 g, 17.1 mmol, 2.0 equiv), tripotassium phosphate (4.54 g, 21.37 mmol, 2.5 equiv), ethanol (8 ml), dimethoxyethane (32.0 ml) and t-butyl acetylene (7.9 g, 97 mmol, 2.0 equiv). The flask was sealed, flushed with nitrogen for three times and stirred at 80° C. for 16 hours. After cooled at room temperature, the reaction mixture was filtered and washed with ethyl acetate (20 ml). The filtrate was concentrated under vacuum and the residue was purified by chromatography (heptanes/ethyl acetate 2/1) to give 4-(4-chloro-phenyl)-cyclohex-3-ene-1,1-dicarboxylic acid diethyl ester (2.2 g, 76%) as colorless oil. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.27 (t, J=8.00 Hz, 6H) 2.29 (t, J=6.38 Hz, 2H) 2.46 (td, J=6.25, 2.02 Hz, 2H) 2.65-2.85 (m, 2H) 4.21 (q, J=8.00 Hz, 4H) 6.07 (m, 1H) 7.26 (s, 4H).
