Carboxylate-Assisted Transition-Metal-Catalyzed C-H Bond Functionalizations: Mechanism and Scope

The development and scope of carboxylates as cocatalysts in transition-metal-catalyzed C-H functionalizations is reviewed. Ryabov and co-workers probed the mechanism of ortho-palladation reactions with N,N-dimethylbenzylamines (DMBA-H, 5) as substrate. Jones and coworkers performed detailed mechanistic studies on the formation of irida- and rhodacycles derived from electron-rich and electron-poor imines, which indicated [Cp*M(OAc)]+ (M = Rh, Ir) to be the key intermediates for acetate-assisted electrophilic activations via transition state. Intermolecular palladium-catalyzed direct benzylations of various five-membered heteroarenes through carboxylate assistance were reported by Fagnou and Lapointe. Dixneuf and Pozgan also reported a ruthenium-catalyzed direct arylation of one 2-phenylpyridine with KOAc as additive.