Tin tetrachloride → Ethyl4-[2,2-dimethyl-4-(5-methyl-thien-2-yl)-benzo[1,2-g]-chrom-3-en-7-yl]benzoate

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Reaction Steps

To a cold (−78° C.) solution of ethyl 4-(diethoxyphosphoryl-3,3-dimethoxypropyl)benzoate (Compound D, 690 mg, 1.75 mmol) in THF (8 mL) was added n-BuLi in hexane (1.6 M solution, 1.1 mL). The mixture was gradually warmed to ambient temperature over 30 min and stirred for 5 minutes. The mixture was recooled to −78° C. and 2,2-dimethyl-4(5-methyl-thien-2-yl)-chrom-3-en-6-al (Compound S, 300 mg, 1.1 mmol) in THF (1 mL) was added to the reaction mixture. The mixture was stirred at ambient temperature for 2 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 material was subjected to flash chromatography on silica gel to obtain the E and Z olefinic compounds, which were dissolved in dichloromethane (5 mL) and cooled to −78° C. A solution of SnCl4 in dichloromethane (52 mg in 0.2 mL) was added to the olefinic compounds. The resulting mixture was stirred for 30 minutes, quenched with methanol, water and diluted with ethyl acetate (100 mL). The organic layer was washed with brine and dried. Solvent was removed under reduced pressure and purified by silicagel chromatography to afford the title compound as a white solid.

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