Iodine-Catalyzed Regioselective Synthesis of Diphenyl-Substituted Carbazoles via [4 + 2] Annulation of β-Formyl Ketones with Indoles

The [4 + 2] annulation of β-formyl ketones with an indole has been developed for the regioselective synthesis of diphenyl-substituted carbazoles in the presence of a catalytic amount of iodine. The 1,4-dicarbonyl compound containing a phenyl group at the α-position of an aldehyde group reacts more readily with indoles to form carbazole derivatives. Using this method, a variety of carbazole derivatives can be readily accessed under mild reaction conditions.