New Synthetic Protocol in Organic Synthesis: Catalytic Functionalization of Unreactive C-H Bonds

Catalytic addition of carbon-hydrogen bonds to olefins and acetylenes takes place with the aid of transition metal complexes. Coordination of a heteroatom to the metal is important for attaining both the C-H bond cleavage and the C-C bond formation. The C-C bond formations occur exclusively at the position ortho or the position β to the directing group. Various aromatic and olefinic compounds such as ketones, esters, aldehydes, imines, imidates, hydrazones, and nitriles can be used in this coupling reaction. The mechanistic studies of the ruthenium-catalyzed reaction of aromatic esters with olefins revealed that there is a rapid equilibrium prior to the C-C bond formation and the C-C bond formation is rate-determining. Catalytic arylation of C-H bond in aromatic ketones with organoboronates gave the ortho arylation products in high yield. The chelation-assisted C-H bond cleavage protocol is also applicable to the regioselective silylation of aromatic C-H bonds with hydrosilanes or vinylsilanes. Various aromatic and heteroaromatic compounds can be used in the silyaltion reaction.