Practical Access to Fused Carbazoles via Oxidative Benzannulation and their Photophysical Properties

An aryne annulation strategy for the synthesis of fused carbazoles is developed using indolyl β-ketonitrile in a cascade manner. The reaction sequence involves aryne-mediated [2 + 2] cycloaddition cleavage and intramolecular Michael addition, followed by oxidation under transition-metal-free reaction conditions. Subsequently, conversion of benzo[b]carbazole-6-carbonitrile to carbazole quinone is observed upon prolongation of the reaction time. Furthermore, these materials exhibit high quantum efficiency, which promotes the light-emitting diode applications.