Recent advances in directing group assisted transition metal catalyzed para-selective C-H functionalization

The transition metal-catalyzed C[sbnd]H activation have been considered as increasingly useful approach for installing new functional groups onto organic small molecules due to their high step- and atom-economy, the abundance of hydrocarbon compounds, and the potential for late-stage functionalization of complex organic molecules. The ortho- and meta-C-H activation and functionalization of aromatic compounds have been widely explored in recent years, however the distal para-C-H activation and functionalization has remained a significant challenge because of the difficulty in forming energetically favorable metallacyclic transition states. The utilization of appropriate directing groups or templates as well as the meticulous design of catalysts and ligands has proven to be effective in transition-metal-catalyzed remote para-C-H bonds activation and functionalization of aromatic compounds. This review aims to summarize the strategies for controlling para-selective C[sbnd]H functionalization using the directing group, template engineering, and catalyst/ligand design under transition metals catalysis in recent years.