An Efficient Synthetic Route towards Novel Furo- and Thieno-triazolopyridines

Tandem Ring‐Opening/Double Ring‐Closing Synthesis of 1,2,4‐Triazolo[1,5‐a]pyridines from Chromone‐Containing Acrylonitriles

“…Finally, the nucleophilic attack of the imine group of compounds 4 aa on the C=O group closed the aromatic triazole cycle, resulting in the 1,2,4‐triazolo[1,5‐ a ]pyridine 3 aa . Also, a similar mechanism for the formation of 1,2,4‐triazolo[1,5‐ a ]pyridines was proposed by Yamagata's group [11] . However, the substrates in that work have a cyano group in the desired position.…”

“…Literature data on the preparation of pyridin-2-ones and pyridin-2-imines from chromones [8,9] as well as construction of 1,2,4-triazolo [1,5-a]pyridines based on pentadienenitrile fragments, [11] suggested the following reaction pathway (Scheme 2). The process starts with a nucleophilic attack of hydrazide 2 a on C-2 of chromone 1 a, which opens the pyran ring.…”

“…Also, a similar mechanism for the formation of 1,2,4-triazolo[1,5-a]pyridines was proposed by Yamagata's group. [11] However, the substrates in that work have a cyano group in the desired position. Thus, the authors did not consider the issue of changing the configuration of the double bond.…”

“…In relation to our work, the study of Yamagata's group (Scheme 1, part c), in which hydrazides were used as 1,3-amphiphilic reagents in the tandem syn-thesis of certain 1,2,4-triazolo[1,5-a]pyridines, [11] turned out to be especially important. Moreover, their substrates are derivatives of vinylfuran and vinylthiophene containing a pentadienenitrile fragment.…”