Veratraldehyde → 3-(3,4-Dimethoxyphenyl)propionic acid

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By boiling Meldrum's acid (formula III with R9 =R10 =methyl group) with veratraldehyde in an ethanolic medium in the presence of formic acid and triethylamine, monoethyl 3,4-di-(methoxy)-benzylmalonate was obtained. According to our experimental observation, diethyl 3,4-di-(methoxy)-benzylidene malonate could not be hydrogenated to diethyl 3,4-di-(methoxy)-benzylmalonate when using formic acid and triethylamine as reagents. Further on we have observed that by reacting veratraldehyde with Meldrum's acid, formic acid and triethylamine at 100° C. for 2 hours and then by boiling with ethanol for 2 hours 3,4-dimethoxyhydrocinnamic acid and not ethyl 3,4-di-(methoxy)-hydrocinnamate was obtained as final product. Thus, the reaction can be interpreted only in such a way that 5-[3',4'-di-(methoxy)-phenylmethyl]-Meldrum's acid is formed in the manner described above, the dioxane ring of which is opened and one carboxyl group of the 3,4-di-(methoxy)-benzylmalonic acid formed is simultaneously esterified. When the temperature of the reaction mixture is increased after removing the ethanol, the carboxyl group is eliminated and 3,4-di-(methoxy)-hydrocinnamic acid ester is obtained.

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