Palladium-Catalyzed Divergent Arylation of Triazolopyridines: A Computational Study.

The mechanisms for new palladium-catalyzed divergent reactions of triazolopyridines were investigated by means of DFT calculations. Previously, it was observed experimentally that cross-coupling at the C7-position of triazolopyridines occurred when a strong base was used, whereas the reaction could be diverted to the C3-position if a weak base was employed. Calculations suggest that a strong base, such as tert-butoxide, can easily deprotonate C7-H, independent of the palladium metal, and deliver the preactivated substrate to palladium, which can reductively eliminate the final product. Without a strong base, the palladium(II) center reacts with the ring-opened diazo imine isomer of triazolopyridine to initially form a palladium(II)-carbene intermediate, which undergoes migratory insertion followed by β-hydride elimination to afford a 1,1-disubstituted alkene.