Visible Light-Induced Catalyst-Free Synthesis of Dibenzo[a,g]carbazoles

Dibenzocarbazoles are a class of important materials used in optoelectronic devices. Their simple and practical construction, therefore, holds great potential from both academic and industrial application aspects. However, the conventional synthetic methods for these compounds often suffer the inadequacies, such as tedious synthetic processes, harsh reaction conditions, limited substrate scope, and high cost. Considering the advantage of the rapid development of photochemistry in organic synthesis, we report a concise and efficient synthetic method for these dibenzo[a,g]carbazole compounds under visible light irradiation. This new protocol enables the reaction to proceed under ambient temperature without any catalyst or metal additives, representing a highly efficient and costeffective pattern. The results infer that the synthesis takes place via 6π electrocyclization and the consequent dehydrogenation in one pot under mild reaction conditions. Starting from the easily available β-tetralone and arylamine, a variety of substrates bearing diverse substituents are smoothly converted into the corresponding dibenzo[a,g]carbazoles with moderate to good yields. It is concluded that the electronic properties of the substituents could not exert a significant influence on the product yield, but the steric hindrance showed an obvious negative effect. This newly developed protocol features the easy availability of starting materials and high cost-efficiency, providing a good alternative for the efficient synthesis of dibenzocarbazoles and their derivatives.