Efficient Synthesis of 3-Substituted 1,2,4-Triazolo[4,3-a]pyridine by [Bis(Trifluroacetoxy)iodo]benzene-Catalyzed Oxidative Intramolecular Cyclization of Heterocyclic Hydrazones

Abstract

A series of 1,2,4-triazolopyridines have been prepared by oxidative intramolecular cyclization of heterocyclic hydrazones with [bis(trifluroacetoxy)iodo]benzene. General applicability of this simple transformation was confirmed by synthesis of 1,2,4-triazolo[4,3-a]pyridine. The advantages of this protocol are the nontoxicity of catalyst and shorter reaction time to obtain good preparative yield.

Keywords:

• [Bis(trifluroacetoxy)iodo]benzene
• hydrazones
• oxidation
• 1,2,4-triazole

ACKNOWLEDGMENT

The author is thankful to Indian Institute of Technology Mumbai, for providing the ¹H NMR facility.

Notes

^a Reagents and reaction conditions: 2-hydrazinopyridine (10 mmol), aldehydes (10 mmol); solvent: ethanol; temperature: reflux temperature; time: 20 min.

^b Starting compound 2-hydrazinopyridine prepared by the standard reported procedure.

^c Isolated yield.

^d Compounds were confirmed by physical constants.

^a Isolated yield after crystallization in benzene.

Note. Catalyst: [bis(trifluroacetoxy)iodo]benzene (11 mmol equivalent); time: 10 min.

^a Reagents and reaction conditions: Hydrazones (10 mmol), [bis-(trifluroacetoxy)iodo]benzene (11 mmol); solvent: anhydrous dichloromethane; temperature: room temperature; time: 10 min.

^b Isolated yield after crystallization and structure were confirmed by ¹H NMR spectra and physical constants.