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.