CATION RADICALS WITH 2-PYRIDYLHYDRAZONES IN NITRILE SOLVENTS S-TRIAZOLO[4,3-ALPHA]PYRIDINES BY THIANTHRENE CATION-RADICAL PERCHLORATE AND 1-(2-PYRIDYL)-1,2,4-TRIAZOLES BY TRIS(2,4-DIBROMOPHENYL)-AMINIUM HEXACHLOROANTIMONATE

Reactions of arenealdehyde 2-pyridylhydrazones (1) with thianthrene ca tion radical (Th+.) and tris(2,4-dibromophenyl)aminium hexachloroantim onate (Ar3N+.SbCl6-) were investigated. The major product was switched depending on the cation radical being used. That is, s-triazolo[4,3-a ]pyridines (2), an intramolecular cyclization product, and 1-(2-pyridy l)-1,2,4-triazoles (3), an intermolecular cycloaddition product, were obtained as a major product when reacted with Th+. and Ar3N+., respect ively in nitrile solvents. The plausible mechanisms are proposed based on both the reduction potentials of Th+. and Ar3N+. and control exper iments.