Nenitzescu indole synthesis: 1929-2019 unexpected formation of a pyrrole-azepine hybrid in the Nenitzescu indole synthesis: A reinvestigation

Abstract

The condensation of 1,4-benzoquinones with enamines reported ninety years ago is a name reaction known as the Nenitzescu indole synthesis which has proved to be a very useful method for obtaining both 5-hydroxyindoles and nonindole derivatives. An unexpected compound containing two condensed azepine rings was isolated in 1988 from the reaction between 1,4-benzoquinone and ethyl 3-aminocinnamate performed in 1-butanol. The reinvestigation of the proposed bisazepine structure by X-ray analysis revealed instead a pyrrole-azepine hybrid having the two heterocycles rings connected by a double bond.