Substrate-Directed C-H Functionalization of 2-Aryl Pyridines by Transition Metal Complexes

摘要

Transition metal mediated C-H activation is a powerful synthetic tool for the total synthesis of complex natural products and biologically active molecules. The strategy involves mainly C-H activation, nucleophilic addition and regeneration of the catalyst. It proceeds through a C-H bond cleavage by ligand coordination to transition metal. Transition metals like Pd, Rh, Ru, Co, and Ir are the most often used catalysts, which form a complex with 2-aryl pyridine and facilitates the functionalization of various C-H bonds to generate diverse C-C and C-X bonds under typically mild reaction conditions with low catalyst loading. In particular, the chelation-assisted cleavage of C-H bonds at ortho-position of the pyridine directing group has been recognized as one of the most powerful strategies for the functionalization of unreactive C-H bonds. Recently, transition metal catalyzed C-H bond activation has received significant interest because it does not require the prefunctionalization of the substrate. Therefore, the metal-catalyzed C-H activation and functionalization is currently considered as atom economy and simplified procedure in comparison with the traditional strategies.