Cleavage of some annulated tetrahydropyridines under the action of dimethyl acetylene dicarboxylate in protic solvents. New practical route to substituted pyrroles and indoles

Tetrahydropyrrolo[3,2-c] pyridines and tetrahydropyrido[4,3-b] indoles undergo piperidine ring opening under the action of dimethyl acetylene dicarboxylate in alcohols or in aqueous dioxane, providing beta-(alk)oxy-substituted pyrroles (indoles) in moderate to high yields.