A Sustainable Access Route to Carbazoles via C-H/C-H Oxidative Functionalization/Cyclization of Arylamines

Carbazole is an important structural motif found in natural products and active pharmaceutical ingredients. In addition, the special optoelectronic properties shown by this class of molecules have led to interesting applications in the field of material science. Given the potential of this N-heterocycle system, we have searched for a novel and more sustainable methodology for their preparation. Herein, we report a novel protocol based on a heterogeneous Pd-catalyzed intramolecular oxidative C-H/C-H coupling methodology, allowing access to carbazoles from variously functionalized diarylamines and triarylamines. Optimal results could be achieved using Pd/C as a heterogeneous catalyst in combination with molecular oxygen at atmospheric pressure. This newly developed methodology allows the facile and clean synthesis of structurally diverse carbazoles, including both natural products and light-emitting molecular entities.