Chloroform → 2-Methoxy-8,9-dihydro-5H-benzo[7]annulen-6(7H)-one

The title compound was synthesized by referring to Tetrahedron Lett., 1977, 21, 1827. To a suspension of methyltriphenylphosphonium bromide (11.5 g) in tetrahydrofuran (50 ml) was added dropwise potassium tert-butoxide (1.0 M solution in tetrahydrofuran) (40 ml) on an ice bath under a nitrogen atmosphere, the solution was stirred for 1 hour, then a solution of 6-methoxy-1-tetralone (4.74 g) in tetrahydrofuran (26 ml) was added dropwise thereto followed by stirring for 2.5 hours at room temperature. Water was added thereto, the solution was stirred, extracted with ethyl acetate, then sequentially washed with water and brine, dried over anhydrous magnesium sulfate, and then the solvent was evaporated in vacuo. The residue was purified by silica gel column chromatography (hexane-ethyl acetate system) to provide 6-methoxy-1-methylene-1,2,3,4-tetrahydronaphthalene (4.4 g). To a solution of thallium(III) nitrate trihydrate (4.5 g) in methanol (40 ml) was added dropwise a solution of 6-methoxy-1-methylene-1,2,3,4-tetrahydronaphthalene (1.7 g) in methanol (13 ml) on an ice bath, and the solution was stirred for 10 minutes at room temperature. Chloroform was added thereto, the solution was stirred, then filtered through celite pad, extracted with diethyl ether, then sequentially washed with water and brine, dried over anhydrous magnesium sulfate, and then the solvent was evaporated in vacuo. The residue was purified by silica gel column chromatography (hexane-ethyl acetate system) to provide the title compound (1.7 g).