A suspension of thallium (III) trifluoroacetate (733 mg 1.35 mmoles) in dichloromethane (12 ml) was cooled in an ice bath, under nitrogen. Ethyl 2-carbethoxy-2-(3,5-dimethoxy-4-hydroxybenzyl)-4-(3,4-methylenedioxyphenyl)butyrate (XIII; R2 = ethyl) (474 mg, 1.00 mmoles) and boron trifluoride etherate (1.45 ml, 11.49 mmoles) were added quickly, the mixture was allowed to come to room temperature, and stirred overnight. Excess aqueous potassium iodide was added, the mixture was stirred for 30 min., made basic with sodium carbonate, and sodium metabisulphite (300 mg, 1.58 mmoles) was added. The thallium (I) iodide was removed by filtration, and washed thoroughly with chloroform. Ethyl acetate was added to the combined filtrate and washings, the organic phase was dried (brine, sodium sulphate) and the solvents were removed. An ether solution of the resulting brown solid (430 mg) was percolated through Florisil. Removal of the solvent gave a yellow oil which deposited fine white needles (260 mg, 55%) on trituration with ether. Crystallization from ether gave 2,2 -dicarbethoxy-1-(4'-hydroxy-3',5'-dimethoxyphenyl)-6,7-methylenedioxytetralin as white needles m.p. 147°-148°.
