From N-benzoylpyridinium imides to pyrazolo[1,5-a]pyridines: a mechanistic discussion on a stoichiometric Cu protocol.

A Cu-mediated preparation of 2-substitiuted pyrazolo[1,5-a]pyridines from N-benzoylpyridinium imides and terminal alkynes is described using stoichiometric Cu(OAc)(2) as both the mediator and the oxidant. Extensive DFT calculations suggest a Cu(III) intermediate via disproportionation of Cu(II).