Efficient Synthesis of Indolyl Benzo[b]carbazoles via Surfactant‐Type Brønsted Acid‐Catalyzed Three‐Component Cyclization of Ortho‐Formylarylketones with Indoles

The surfactant‐type Brønsted acid‐catalyzed multi‐component cascade reaction of ortho‐formylarylketones with indoles was investigated in an aqueous medium for the synthesis of indolyl benzo[b]carbazoles. The reaction was carried out in the presence of dodecylbenzenesulfonic acid, which was initiated by two consecutive nucleophilic additions of indoles to the aldehyde group of ortho‐formylarylketones, followed by a Friedel−Crafts‐type cyclization and dehydrative aromatization. This protocol afforded the desired products in good yields under mild conditions and demonstrated a broad substrate scope.