Pyrido[1,2-c][1,2,4]triazol-3-ylidene: reactivity and its application in organocatalysis and organometallic catalysis.

The reactivity and catalytic performance of 2-ethylpyrido[1,2-c][1,2,4]-triazol-3-ylidene 6 have been comprehensively investigated. The carbene 6 has shown unusual properties owing to the effect of the pyrido-annulation. While formohydrazide 8 and hydrazine 9 are obtained via the destruction of the triazole skeleton of the carbene, 3-((1Z,3E)-4-(1H-pyrrol-1-yl)buta-1,3-dienyl)-1-ethyl-1H-1,2,4-triazole 10 is achieved through the cleavage of the C-N bond of the pyridine ring. The carbene has turned out to be a powerful catalyst in a variety of organocatalyzed and Pd(II)-catalyzed transformations.