To a cold (-78° C.) solution of ethyl 4-(diethoxyphosphoryl-3,3-dimethoxypropyl)benzoate (Compound D, 1.4 g, 3.6 mmol) in THF (9 mL) was added n-BuLi in hexane (1.6M solution, 2.8 mL). The mixture was gradually warmed to ambient temperature over 30 minutes and stirred for 5 minutes. To this mixture was added 2,2-dimethyl-4(tol-4-yl)-chrom-3-en-6-al (Compound Q, 260 mg, 0.93 mmol) in THF (1 mL) at ambient temperature and the mixture was stirred for 5 hours. The reaction mixture was diluted with ethyl acetate (100 mL) and washed with brine (10 mL) dried and the solvent was removed by evaporation. The residual material was subjected to flash chromatography on silicagel to obtain the E and Z olefinic compounds, which were dissolved in dichloromethane (5 mL) and cooled to -50° C. A solution of SnCl4 in dichloromethane (150 mg in 0.7 mL) was added to the olefinic compounds. The reaction mixture was gradually warmed to -10° C. over 3hours and then quenched with methanol and water. The reaction mixture was diluted with ethyl acetate (100 mL). The organic layer was washed with brine and dried. Solvent was removed under reduced pressure and the residue purified by chromatography on silicagel to afford the title compound as a white solid.
