Regioselective Synthesis of Polysubstituted Carbazoles from Indoles and Simple Dicarbonyl Compounds

Polysubstituted carbazoles were efficiently synthesized through direct benzannulation reaction between 1,4‐dicarbonyl compounds and indoles with catalytic amount of inexpensive zirconium(IV) chloride. This transformation proved to be regioselective and furnishes 1,4‐disubstituted and 1,2,4‐trisubstituted carbazoles with yields ranging from 26% to 91% and broad substrate scope. Moreover, this protocol benefits from using readily accessible starting materials without the need of their pre‐functionalization. The synthetic utility of the products was exemplified by functionalization of an iodocarbazole by means of Suzuki‐Miyaura reactions and by the synthesis of a 3‐deaza‐derivative of the natural product canthin‐6‐one.