Copper-catalyzed [4 + 2] annulation reaction of ß-enaminones and aryl diazonium salts without external oxidant: Synthesis of highly functionalized 3: H -1,2,4-triazines via homogeneous or heterogeneous strategy

Herein, both homogeneous and heterogeneous strategies were developed to access highly functionalized 3H-1,2,4-triazines using Cu-catalyzed [4 + 2] annulation. This new protocol featured external oxidant-free conditions, a non-noble copper catalyst and good functional group compatibility. The multiple valence states of copper were further confirmed by X-ray photoelectron spectroscopy.