Facile One-Pot Synthesis of [1,2,3] Triazolo[ 1, 5-a] Pyridines from 2Acylpyridines by Copper(II)-Catalyzed Oxidative N-N Bond Formation

An efficient and simple method for the synthesis of various [1,2,3]triazolo[1,5-a]pyridines has been established. The method involves a copper(II)-catalyzed oxidative NN bond formation that uses atmospheric oxygen as the terminal oxidant following hydrazonation in one pot. The use of ethyl acetate as the solvent dramatically promotes the oxidative NN bond-formation reaction and enables the application of oxidative cyclization in the efficient one-pot reaction. A mechanism for the reaction was proposed on the basis of the results of a spectroscopic study.