Transition-metal-catalyzed ortho-selective C−H functionalization reactions of free phenols

Phenols are important readily available chemical feedstocks and versatile synthetic building blocks for diverse synthetic transformations. Their motifs are prevalent in a diverse array of natural products, pharmaceuticals, functional materials, and privileged chiral ligands. Consequently, the development of facile and direct site-selective C–H bond functionalization of free phenols is of great importance and considerable interest to both industry and academic research. Over the past decades, transition-metal-catalyzed C–H bond functionalization has become as a powerful synthetic tool in organic synthesis. In this review, we provide a brief overview of recent progress in the transition-metal-catalyzed direct ortho-selective C−H functionalization of free phenols.