Palladium‐Catalyzed Regioselective C−H Arylation of 4‐Azaindazole at C3, C5 and C7 Positions

Direct and site-selective C5 and C7 palladiumcatalyzed C-H arylations of 4-azaindazole N-oxide have been achieved. A bidentate ligand and Pd(OAc)2 catalyst in toluene promoted the activation of C5 position, while a phosphine ligand and PdCl2 catalyst in DMA directed the arylation at C7 position. Using this new method, the synthesis of C5, C7-diarylated 4-azaindazole N-oxides as well as the C3, C5 C7 triarylated 4-azaindazoles was achieved towards future medicinal compound development.