Direct synthesis of aryl-annulated []carbazoles by gold(i)-catalysed cascade reaction of azide-diynes and arenes.

The gold-catalysed annulation of conjugated alkynes bearing an azido group with arenes gave annulated []carbazoles. Using benzene, pyrrole, and indole derivatives as the nucleophiles, benzo[]-, pyrrolo[2,3-]-, and indolo[2,3-]carbazoles were produced, respectively. The reaction proceeded through pyrrole and benzene ring construction accompanied by the formation of two carbon-carbon and one carbon-nitrogen bond and the cleavage of two aromatic C-H bonds. The mechanism of the reaction with pyrrole was investigated by density functional theory calculations. ,'-dimethylated indolo[2,3-]carbazole showed dual ultraviolet-visible-near-infrared and fluorescence spectral changes upon electrolysis.