Synthesis of Indolo[1,2-a]quinoxalinones through Pd/Cu-cocatalyzed Oxidative Isocyanide-insertion Cyclizations of Indoles and Hydrolysis of Enamines

A novel Pd/Cu-cocatalyzed isocyanide-insertion cyclizations of indoles and hydrolysis of enamines has been developed for the construction of indolo[1,2-a]quinoxalinones. The secondary amine group on the N-phenylindole skeleton acted as important directing groups to participate in C2 position activations of indoles and the following isocyanide insertion cyclizations. The fragile generated enamine bond was easily hydrolyzed by the acid medium and afforded the corresponding quinoxalinone skeletons. This regioselective and high-yielding transformation, avoiding the utilizations of traditional hazardous gas CO could be extended to its applications for the synthesis of the natural polycyclic products.