Palladium-Catalyzed Benzannulations of 1-(Indol-2-yl)but-3-yn-1-ols: Easy Access to Functionalized Carbazoles.

An atom-economical direct synthesis of carbazoles having aryl and aryl ketone groups has been achieved through Pd(II)-catalyzed cascade reactions between 1-(indol-2-yl)but-3-yn-1-ols and aldehydes. The reaction proceeds through alkyne-carbonyl metathesis, an uncommon pathway using palladium catalysts, and constitutes a fast intermolecular assembly through four carbon-carbon bond formations in one pot. Absence of the aldehyde substrate resulted in the formation of C4-aryl-substituted carbazoles. The reaction is amenable to the synthesis of biscarbazole derivatives.