Rearrangement of Arylhydrazones of α,β-Unsaturated Carbonyl Compounds in Polyphosphoric Acid. 6

Article abstract of DOI:10.1021/jo00197a009

The reactions of a series of N-methyl-N-arylhydrazones of α,β-unsaturated carbonyl compounds 1 with hot polyphosphoric acid are described.Three main courses were observed, depending on the structure of the carbonyl portion of the substrate.Unsaturated α-oxo ester hydrazones (1a-c) rearranged to give substituted 3-<2-(methylamino)aryl>-2-oxo-3-butenoic acid esters (2a-c); the reaction mechanism strictly resembles the initial steps of the Fischer indole synthesis.Unsaturated aldehyde hydrazones alternatively gave either the di-3-indolylmethane derivatives (3a,b) or the amino nitriles (4a-c).The first process develops through intermediates structurally similar to 2; the latter was demonstrated to be exclusively intramolecular.