3-Hydroxypyrroles. I. A general synthetic route to 4,5-unsubstituted alkyl 3-hydroxpyrrole-2-carboxylates.

The synthesis of 4, 5-unsubstituted alkyl 3-hydroxypyrrole-2-carboxylates was described. An equimolar mixture of glycine esters (6) and diethyl ethoxymethylenemalonate (7) gave the condensation products (8) with liberation of ethanol. 3-Hydroxypyrrole-2, 4-dicarboxylates (9) were obtained by the Dieckmann condensation of 8 using alkoxide as condensing agent. Selective partial hydrolysis of pyrrole-diesters (9) using a large excess of alkali hydroxide afforded the 4-carboxylic acids (10), which readily gave alkyl 3-hydroxypyrrole-2-carboxylates (5) on decarboxylation in boiling β-picoline or pyridineacetic acid in good yields.