Synthesis of some 1‐methyl‐3‐alkoxy‐5‐arylpyrrolecarboxylic acids and derivatives

By a combination of hydrolysis, decarboxylation, and methylation diethyl 1‐methyl‐3‐hydroxy‐5‐phenylpyrrole‐2,4‐dicarboxylate was converted into 1‐methyl‐3‐methoxy‐5‐phenyl‐pyrrole‐2,4‐dicarboxylic acid (5) and into the isomeric compounds ethyl 1‐methyl‐2‐phenyl‐4‐methoxypyrrole‐3‐carboxylate (4a) and ethyl 1‐methyl‐3‐methoxy‐5‐phenylpyrrole‐2‐carboxylate (9a). 1‐Methyl‐2‐phenyl‐4‐methoxypyrrole‐3‐carboxylic acid was synthesized both by the selective decarboxylation of 5 and by the hydrolysis of 4a. Hydrolysis of 9a, however, did not give the corresponding acid, but rather an oxidation product, 1‐methyl‐3‐methoxy‐5‐hydroxy‐5‐phenyl‐3‐pyrrolin‐2‐onc (10a). Compound 10a was shown to arise from the air oxidation of the completely decarboxylated product, 1‐methyl‐2‐phenyl‐4‐methoxypyrrole. Reduction of 9a with lithium aluminum hydride gave 1‐methyl‐3‐methoxy‐5‐phenylpyrrole‐2‐methanol, which yielded 10a upon oxidation with silver oxide.