Thallium (III) trifluoroacetate (6.5 g; 11.96 mmoles) was suspended in 1,2-dichloroethane (75 ml) and heated to reflux under nitrogen. Ethyl 2-carbethoxy-2-(3,5-dimethoxy-4-hydroxybenzyl)-4-(3,4-methylenedioxyphenyl)butyrate (XIII) (4.2 g, 8.86 mmoles) in 5 ml of 1,2-dichloroethane was then added and the reaction mixture became deep red. Refluxing was continued for 30 min. The solution was cooled, poured into saturated sodium bisulfite, and turned yellow. The aqueous layer was extracted with ethyl acetate and the organic layer was washed with saturated sodium bicarbonate, water, and saturated brine, and was dried over sodium sulfate. Filtration and evaporation gave a brown oil which was dissolved in 50 ml of acetone. To this was added 3 ml of dimethyl sulfate and 18 g of anhydrous potassium carbonate. This mixture was refluxed overnight, cooled and poured into water. The aqueous phase was extracted with chloroform and the chloroform was washed with water and saturated brine, and dried over sodium sulfate. Filtration and evaporation gave a brown oil which, when triturated with methanol, gave 1.8 g of the title product (XIV-b; R2 = ethyl). Chromatography of the methanol residue on silica gel (1/l ether/cyclohexane) gave an additional 0.5 g (55% total yield). Recrystallization from methanol gave a white solid (mp 149°-152°).
