A jackpot C–H activation protocol using simple ruthenium catalyst in deep eutectic solvents†
Deep eutectic solvents (DESs) have been used for the first time as a sustainable medium in a ruthenium-catalyzed C–H activation reaction. This study describes an efficient, simple and straightfoward protocol for the direct C–H activation of a broad range of aromatic substrates and reaction with several olefins and alkynes, affording interesting heterocyclic systems as products. A simple, robust and commercially available ruthenium catalyst was used along with different DESs under different reaction conditions. This methodology was compatible with the use of either internal or external oxidant (oxygen from air) using a catalytical amount of copper salts for the last case. Different functional directing groups were well tolerated obtaining promising results, that were comparable and even better that those reported in the literature. Also, the reaction medium could be recycled up to 3 consecutive times and this transformation could be carried out on a gram scale with excellent yield. Several green chemistry mass metrics, such as reaction mass efficiency, process mass intensity and optimum efficiency, as well as qualitative parameters were calculated and compared with those of the classical protocols, showing the advantages of using DESs for C–H activation processes.