Recent Developments in Transition Metal-Catalyzed Cross-Dehydrogenative Coupling Reactions of Ethers and Thioethers

Cross-dehydrogenative coupling of two C-H bonds or a C-H and an X-H bond (X=N, O, P, S, etc.) has emerged as a powerful new synthetic methodology in the last 12 years. Using this approach, simple ethers, often utilized as solvents, and more complex ones, as well as thioethers, have become important alkylating agents, when reacted directly, under oxidative conditions in the presence of suitable reagents. This environmentally friendly, sustainable procedure, has been used to alkylate a wide range of substrates, from simple ketones and acids to alkyl benzenes, coumarins, indoles, oxazoles, benzoxazoles or (benzo)thiazoles and more. This Review is a systematic presentation of the developments in transition metal-catalyzed CDC reactions, including photoredox processes, which took place between 2014 and early 2018, with an emphasis on the later years.