Divergent Synthesis of Functionalized 1,2,4-Triazoles and 1,3,4-Oxadiazoles via a Microwave-Assisted [3 + 2] Annulation of Heteroaryl Carbonitriles with Arylhydrazides: A Synthetic and Density Functional Theory Study

The functional group interconversion of heteroaryl carbonitriles and benzohydrazides via microwave-assisted organic synthesis presents an opportunity to construct (1H)-1,2,4-triazole, 1,3,4-oxadiazole, or 1,3,4-thiazoles contingent on the electronic environment of the heteroaryl carbonitrile and benzohydrazide. The developed reaction protocol is atom economical, involving only the carbonitrile and benzohydrazide synthons and producing only water, or ammonia, as byproducts. The reaction strategy is free of metals and external oxidants and scalable. Complete chemoselectivity is achievable. This synthetic approach affords entry into a new class of non-C2-symmetric, tridentate, soft-N-donor complexants with potential utility in the selective separation of minor actinides from lanthanides in spent nuclear fuel toward potential closure of the nuclear fuel cycle. Synthetic method development, complexant and heteroaryl substrate scope, competition, application, and scale-up experiments as well as DFT calculations are reported herein.