Brønsted-Acid-Catalyzed Friedel–Crafts Reaction and Electrocyclization Cascade of Indoles with α‑Functionalized Carbonyls

Reported here is an efficient Friedel–Crafts-type reaction followed by electrocyclization cascade under an air atmosphere, employing readily available building blocks as starting materials, ethanol as a solvent, and Brønsted acid as a catalyst. On the basis of the cascade strategy, 2-(2-aminophenyl)-9H-carbazole has been furnished with excellent regioselectivity, exceptional functional group tolerance, and tolerated large-scale synthesis. Furthermore, one-pot syntheses of quino­[3,4-a]­carbazoles have been accomplished, demonstrating the broad synthetic utility of this strategy in the synthesis of valuable heteroaryl-annulated [a]­carbazoles.