Copper-Catalyzed Three-Component Formal [3+1+2] Benzannulation for Carbazole and Indole Synthesis

Three-component formal [3 + 1 + 2] benzannulation reactions of indole-3-carbaldehydes or 1-methyl-pyrrole-2-carbaldehydes with two different molecules of saturated ketones have been successfully developed under Cu-catalyzed and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated conditions. Various unsymmetrically substituted carbazoles and indoles were obtained up to 95% yield. Furthermore, the resulting products exhibit unusual aggregation-induced emission (AIE) properties in the solid state. This method features high atom-economy, cheap catalysts and oxidants, wide substrate scope, and saturated ketones as one-carbon and two-carbon sources, thus providing an efficient approach to polycyclic carbazole and indole compounds.