Electrochemical synthesis of 1,2,4-triazole-fused heterocycles

A reagent-free intramolecular dehydrogenative C-N cross-coupling reaction has been developed under mild electrolytic conditions. In this atom- and step-economical one-pot process, valuable 1,2,4-triazolo[4,3-a] pyridines and related heterocyclic compounds could be synthesized efficiently from commercially available aliphatic or (hetero) aromatic aldehydes and 2-hydrazinopyridines. Various functional groups are compatible with this metal- and oxidant-free protocol which can be carried out on a gram scale easily. This novel method was applied to the synthesis of one of the top-selling drugs Xanax and late stage functionalization for generating chemical diversity in biologically relevant lead molecules.