Formation of 1,2,4-Triazoles by Cation Radical Induced Oxidative Addition of Arylhydrazones of Benzaldehyde and Butyraldehyde to Nitriles

Article abstract of DOI:10.1021/jo00253a029

1,3,5-Trisubstituted 1,2,4-triazoles have been made in excellent yields by oxidative cycloaddition of arylhydrazones of benzaldehyde and butyraldehyde to aceto-, propio-, and acrylonitrile.Oxidation was achieved with the cation radicals thianthrenyl perchlorate (Th^(radical)+ClO4^-) and tris(2,4-dibromophenyl)aminium hexachloroantimonate (Ar3N^(radical)+SbCl6^-).The triazoles thus had a phenyl, p-nitrophenyl, or 2,4-dinitrophenyl group in the 1-position, either a phenyl or propyl group in the 3-position, and a methyl, ethyl, or vinyl group in the 5-position.The formation of 5-vinyltriazoles was confirmed by their hydrogenation to 5-ethyltriazoles, which were obtained also by cycloadditions to propionitrile.New triazoles (eight) were also synthesized by a known alternative route, but in lower yields.The fact that 5-vinyltriazoles were formed instead of 5-cyano-2-pyrazolines shows that cation radical induced cycloadditions do not go through the nitrilimines.Cycloadditions with N-phenylbenzohydrazonoyl chloride and acrylonitrile in the presence of aluminum chloride and of triethylamine were carried out for comparison with the corresponding cation radical reaction.