Counter anions modulate selectivity in the divergent copper-catalyzed dehydrogenation of cyclohexanones

Dehydrogenation of carbon-carbon bonds to form valuable unsaturated products is an important transformation in chemistry. Cyclohexanones have been reported to form either phenol or semi-oxidized enone products via precious metal catalysis. Divergent catalytic systems for these transformations are highly desirable but remain scarce. Here, we report a mild, cost-effective, copper-catalyzed, switchable dehydrogenation of cyclohexanones to phenols or enones via silyl enol ethers. β-Diketiminate ligands are found to be crucial for the dehydrogenation, and the counter anions of the simple and commercially available copper salts maintain the selectivity. The current system exhibits efficient catalytic competency for various cyclohexanones and heterocycles with high-functional group tolerance, and the procedure is quite convenient, using a simple combination of enols, oxidant, and copper catalyst/ligand under neutral conditions. Mechanistic studies, including computational and experimental studies, disclose that the basicity and nucleophilicity of the counter anions tune the reaction pathways.