Ruthenium(II)-Catalyzed C–H Bond Activation and Functionalization

Organic reactions that involve the direct functionalization of non-activated C–H bonds represent an attractive class of transformations which maximize atom- and step-economy, and simplify chemical synthesis. Due to the high stability of C–H bonds, these processes, however, have most often required harsh reaction conditions, which has drastically limited their use as tools for the synthesis of complex organic molecules. Following the increased understanding of mechanistic aspects of C–H activation gained over recent years, great strides have been taken to design and develop new protocols that proceed efficiently under mild conditions and duly benefit from improved functional group tolerance and selectivity. In this review, we present the current state of the art in this field and detail C–H activation transformations reported since 2011 that proceed either at or below ambient temperature, in the absence of strongly acidic or basic additives or without strong oxidants. Furthermore, by identifying and discussing the major strategies that have led to these improvements, we hope that this review will serve as a useful conceptual overview and inspire the next generation of mild C–H transformations.

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Mild metal-catalyzed C–H activation: examples and concepts

Transition metal-catalyzed direct functionalization of C–H bonds is one of the key emerging strategies that is currently attracting tremendous attention with the aim to provide alternative environmentally friendly and efficient ways for the construction of C–C and C–hetero bonds. In particular, the strategy involving regioselective C–H activation assisted by various functional groups shows high potential, and significant achievements have been made in both the development of novel reactions and the mechanistic study. In this review, we attempt to give an overview of the development of utilizing the functionalities as directing groups. The discussion is directed towards the use of different functional groups as directing groups for the construction of C–C and C–hetero bonds via C–H activation using various transition metal catalysts. The synthetic applications and mechanistic features of these transformations will be discussed, and the review is organized on the basis of the type of directing groups and the type of bond being formed or the catalyst.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

Significant progress has been accomplished in direct olefinations through twofold C–H bond functionalization of arenes and heteroarenes employing readily accessible, selective and relatively inexpensive ruthenium catalysts. Particularly, ruthenium(II) complexes have allowed challenging direct double C–H/C–H bond alkenylations of arenes with ample scope. These catalysts set the stage for step-economical C–H/C–H bond functionalization with electron-rich as well as electron-deficient arenes and heteroarenes, and, thereby, provide versatile access to diversely decorated styrenes.

Ruthenium-catalyzed direct oxidative alkenylation of arenes through twofold C–H bond functionalization

Ruthenium-catalyzed oxidative C-H bond olefination of N-methoxybenzamides using an oxidizing directing group.

Ruthenium-Catalyzed Pyrrole Synthesis via Oxidative Annulation of Enamides and Alkynes

The title reaction affords either N-acetyl-substituted or N-unsubstituted pyrrole derivatives in dependancy on conditions used.

Nuancheng Wang

Papers

Ruthenium-catalyzed oxidative C-H bond olefination of N-methoxybenzamides using an oxidizing directing group.

Ruthenium-Catalyzed Pyrrole Synthesis via Oxidative Annulation of Enamides and Alkynes

Ruthenium‐Catalyzed Pyrrole Synthesis via Oxidative Annulation of Enamides and Alkynes.