Palladium-Catalyzed Regioselective Arylation of Pyrazolo[1,5‑a]pyridines via C–H Activation and Synthetic Applications on P38 Kinase Inhibitors

A direct arylation of pyrazolo­[1,5-a]­pyridines with aryl iodides selectively occurring at the C-3 and C-7 positions via palladium-catalyzed C–H activation is described. In these reactions, (a) cesium­(I) fluoride and (b) silver­(I) carbonate were employed as the additive to afford 3- and 7-arylated pyrazolo­[1,5-a]­pyridines, respectively, in modest to good yields. These reactions showed good compatibility with functional groups, and the catalytic mechanisms of these reactions were proposed. Finally, the synthetic application on the potent p38 kinase inhibitors was demonstrated.