Reaction of primary and secondary enamines with anhydrides of unsaturated dicarboxylic acids

It was established that donor-acceptor complexes are formed in the reaction of some conjugated enamines with anhydrides of unsaturated dicarboxylic acids; in all likelihood, this constitutes evidence in favor of a scheme that includes nucleophilic addition of the enamine to the double bond. Addition of this type with subsequent intramolecular cyclization leads to the formation of ²-pyrrolin-5-ones. In the case of citraconic anhydride it is shown (on the basis of data from the PMR and mass spectra) that nucleophilic attack is directed to the unsubstituted carbon atom of the ethylene bond.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 474–476, April, 1977.