Piperonal → 2-Bromo-4, 5-methylenedioxyphenylpropiolic acid

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Bromination of piperonal (1) readily gave 6-bromopiperonal (2) which was conveniently converted to ethyl-2-bromo-4,5-methylenedioxyphenylpropiolate (3) by treatment with triethyl phosophonoiodoacetate under the general conditions devised by Wadsworth and Emmons for the synthesis of propiolate esters. The corresponding 2-bromo-4, 5-methylenedioxyphenylpropiolic acid (4) was obtained by alkaline hydrolysis of the ester (crude). Treatment of compound (4) with dicyclohexylcarbodiimide in DMSO to form the anhydride followed by closure of the ring yielded 5-bromo-7,8-methylenedioxy-1-(2′-bromo-4′,5′-methylenedioxyphenyl)napthalene-2,3-dicarboxylic acid anhydride (5), 1-bromo-6,7-methylenedioxy-4-(2′-bromo-4′, 5′-methylenedioxyphenyl)napthalene-2,3-dicarboxylic acid anyhdride (6) and 6,7-methylenedioxy-1-(2′-bromo-4′,5′-methylenedioxyphenyl)napthalene-2,3-dicarboxylic acid anhydride (7). The conversion of the dibromo-anhydride 5 into 2,3-dihydroxymethyl-5-bromo-7,8-methylenedioxy-1-(3′, 4′-methylenedioxyphenyl)napthalene (8) and 2,3-dihydroxymethyl-5,6-methylenedioxy-4-(3′,4′-methylenedioxyphenyl)napthalene (9) was accomplished on using lithium aluminum hydride and aluminum chloride in THF. Selective oxidation of compound 9 using silver carbonate -celite reagent yielded 7,8-methylendioxy-1-(3′,4′-methylenedioxyphenyl)-3-hydroxymethylnapthalene-2-carboxylic acid lactone (10) and 7,8-methylenedioxy-1-(3′,4′-methylenedioxyphenyl)-2-hydroxymethylnaphthalene-3-carboxylic acid lactone (11).

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