Rh(III)‐Catalyzed Reaction of 2‐Aryl‐3‐acyl‐1H‐indoles with α‐Diazo Carbonyl Compounds: Synthesis of 5‐Carbonyl Substituted Benzo[a]carbazoles via [5+1] Annulation

Abstract In this paper, an efficient synthesis of 5‐carbonyl substituted benzo[a]carbazoles via Rh(III)‐catalyzed [5+1] annulation reaction of 2‐aryl‐3‐acyl‐1H‐indoles with α‐diazo carbonyl compounds is presented. The cascade process is accomplished by a C−H bond alkylation, cyclization and aromatization. Notably, this novel method features broad substrate compatibility and good functional group tolerance. In addition, the synthetic applications of this protocol have also been demonstrated by gram‐scale synthesis and derivatization to an antitumor agent.