New Rearrangements of Arylhydrazones in Polyphosphoric Acid: Extension to the Thiophene and Indole Series. 5

Article abstract of DOI:10.1021/jo00348a016

The behavior toward polyphosphoric acid of arylhydrazones of a few heterocyclic carbonyl compounds of the thiophene and indole series is described.The phenylhydrazone and 2,6-dimethylphenylhydrazone of ethyl α-thienylglyoxylate gave ethyl 4- and 5-(4-aminoaryl)-α-thienylglyoxylate, arising from two different sigmatropic rearrangements.The N,3,5-trimethylphenylhydrazone of 2-methylindole-3-carboxaldehyde afforded the 4-<4-(methylamino)-2,6-dimethylphenyl>-2-methylindole-3-carboxaldehyde resulting from a <5,5> sigmatropic rearrangement, while the 2,6-dimethylphenylhydrazone of the same carbonyl compound unexpectedly gave the 3-(4-amino-3,5-dimethylphenyl)-2-methylindole-3-carboxaldehyde generated through a <3,5> sigmatropic reaction.Chemical evidences are given for the assigned structures.