New method for synthesis of triazolo[1,5-a]pyridines from N‘-[bis(methylthio)methylene]cyanoacetohydrazide and push pull systems

Abstract

The N’-[bis(methylthio)methylen]cyanoacethydrazides derived from cyanoacethydrazide possess the structural requirements for the formation, in basic media of methylenic carbanions which make possible the synthesis of interesting heterocyclic systems with potential activity. On the other hand, it is known that the triazolo[1,5a]pyridines are very useful compounds as pharmaceutical agents for the treatment of several diseases. Their synthesis usually requires several steps and even in the most simple cases, good yields could be not achieved. In this paper, the direct synthesis of new triazolo[1,5a]pyridines is described , which is advantageous in relation to the other methods reported. All reactions were carried out at room temperature using several basic media without satisfactory results. The best yields could be obtained by reflux temperature in presence of sodium ethoxide. Reaction mechanisms were proposed, which explain clearly the formation of these condensed heterocycles starting from the nucleophilic attack of the corresponding carbanion to the electrophilic C-atom of keten-S,S-acetals and dithiethane push pull systems. The best results were obtained with the former ethylenicones. The compounds synthesized were characterized through their quantitative elemental analysis and spectroscopic techniques (IR, 1H and 13C-NMR and mass spectrometry).