Selective Synthesis of Benzo[a]Carbazoles and Indolo[2,1‐a]‐Isoquinolines via Rh(III)‐Catalyzed C−H Functionalizations of 2‐Arylindoles with Sulfoxonium Ylides

Abstract A highly chem‐ and regioselective synthesis of diversely substituted benzo[a]carbazoles and indolo[2,1‐a]‐isoquinolines through Rh(III)‐catalyzed cascade reactions of 2‐arylindoles with sulfoxonium ylides is presented. To be specific, treatment of 2‐arylindoles, 2‐arylindole‐3‐carbaldehydes, 2‐arylindole‐3‐carbonitriles or 2‐aryl‐3‐methylindoles with sulfoxonium ylides under the catalysis of Rh(III) led to the selective formation of 6‐aryl/alkyl benzo[a]carbazoles, 5‐acylbenzo[a]carbazoles, 6‐amino‐5‐acylbenzo[a]carbazoles or 12‐methylindolo[2,1‐a]isoquinolines, respectively. Mechanistically, the formation of the title compounds involves a cascade process including metalation of the inert C(sp2)−H bond, migratory insertion of ylide into the carbon‐metal bond via an in situ carbenoid formation, protodemetalation, and condensation. To our knowledge, this is the first example in which β‐carbonyl sulfoxonium ylides were used as stable carbene precursors and bifunctional C2 synthons to afford benzo[a]carbazoles and indolo[2,1‐a]isoquinolines. magnified image