Syntheses of gallic acid and pyrogallol

Abstract

Condensation of trimethyl propane-1,2,3-tricarboxylate (I) with dimethyl dimethoxymalonate (II) gave the cyclic β-keto-ester (III) and a smaller amount of a phenolic acid (IV). Treatment of the ester (III) with acid yielded gallic acid. Condensation of dimethyl glutarate with the diester (II) yielded the cyclic β-keto-ester (V), which was converted into 4,5,6-trihydroxyisophthalic acid (IX) on treatment with acid. The latter decarboxylated smoothly at 200 °C to give pyrogallol.