Synthesis of furo[2,3-f]- and furo[3,2-e]indole derivatives

Two compounds — the diethylamides of 1,2-dimethyl-3-carbethoxy-6-carboxyfuro2,3-f]- and 1,2-dimethyl-3-carbethoxy-5-carboxvfuro3,2-e]indoles — are formed in the reaction of 1,2-dimethyl-3-carbethoxy-5-hydroxyacetic acid (I) with dimethylformamide and phosphorus oxychloride as a result of subsequent intramolecular cyclization of the intermediates. This constitutes evidence for formylation of the starting acid in the 6 and 4 positions. Formylation of the ethyl ester of acid I gives only the 6-formyl derivative, the intramolecular cyclization of which under the influence of sodium ethoxide gives 1,2-dimethyl-3,6-dicarbethoxyfuro2,3-f]-indole. Hydrolysis of the latter with alcoholic alkali gives the corresponding dicarboxylic acid. The structures of the synthesized compounds were confirmed by the PMR, IR, and mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 766–769, June, 1977.