Versatile Synthesis of Polyfunctionalized Carbazoles from (3-Iodoindol-2-yl)butynols via a Gold-Catalyzed Intramolecular Iodine-Transfer Reaction

The controlled gold-catalyzed preparation of 3-iodo 2,4,6-trisubstituted 9 H -carbazoles has been developed by starting from (3-iodoindol-2-yl)butynols. These results could be explained through an initial 6- endo -dig alkyne carbocyclization by chemo- and regiospecific attack of the C3-indole position at the external alkyne carbon followed by a stepwise 1,3-iodine transfer and dehydration. This reaction outcome for the gold-catalyzed transformation of (3-iodoindol-2-yl)alkynols sharply contrasts with that observed for conventional metal-catalyzed processes of iodoarenes, because iodine transfer is feasible. This selective reaction has been studied experimentally; additionally, its mechanism has been investigated by means of density functional theory calculations.