Hydroarylations by cobalt-catalyzed C-H activation.

As an earth-abundant first-row transition metal, cobalt catalysts offer a broad range of economical methods for organic transformations via C-H activation. One of the transformations is the addition of C-H to C-X multiple bonds to afford alkylation, alkenation, amidation, and cyclization products using low- or high-valent cobalt catalysts. This hydroarylation is an efficient approach to build new C-C bonds in a 100% atom-economical manner. In this review, the recent developments of Co-catalyzed hydroarylation reactions and their mechanistic studies are summarized.