Access to 1,3- and 1,5-Disubstituted 1,2,4-Triazoles by Condensation of Acyl Hydrazides with Formamidinium Acetate

Abstract A simple redox-neutral method for the regioselective preparation of 1,3- and 1,5-disubstituted 1,2,4-triazoles from the corresponding unactivated acyl hydrazides and the inexpensive, non-toxic, and shelf-stable formamidinium acetate was developed. The addition of zinc salts proved to be pivotal to ensure full regioselectivity for the 1,3-disubstitution pattern, while 1,5-disubstituted 1,2,4-triazoles could be accessed without. A variety of sensitive functional groups were tolerated, and [1,2,4]triazolo[4,3-a]pyridines were obtained from the corresponding 2-hydrazopyridines without Dimroth rearrangement.