Palladium-Catalyzed Regioselective Oxidative Annulation of Cyclohexanones and 2-Aminophenyl Ketones Using Molecular Oxygen as the Sole Oxidant

A facile oxidative annulation of cyclohexanones and 2-aminophenyl ketones that uses molecular oxygen as the sole oxidant is described. The reaction provides a direct approach to acridines, a structural motif for a large number of fluorescent sensors, functional materials, ligands, and pharmaceuticals. In the presence of a palladium catalyst, high regioselectivity is observed when using non-symmetric 3-substituted cyclohexanones. With the use of oxygen as the terminal redox moderator, the electron gap of the global redox condensation process is filled and the reaction efficiency is significantly promoted. This protocol possesses many advantages such as using non-hazardous oxidant and readily available starting materials, high regioselectivity, and water as the only by-product. (Figure presented.).