Fused Ring Construction around Pyrrole, Indole, and Related Compounds via Palladium-Catalyzed Oxidative Coupling with Alkynes

The selective synthesis of 1,2,3,4-tetrasubstituted carbazoles can be performed effectively through the palladium-catalyzed oxidative coupling reactions of N-substituted indoles or their carboxylic acid derivatives with alkynes. Unsyrnmetrically octasubstituted carbazoles can also be obtained by the stepwise couplings of 1-methylpyrrole-2-carboxylic acid with two different alkynes. In addition, the present coupling procedure is applicable to the synthesis of other various heteroarenes possessing di-, tri-, and tetracyclic cores. Some of the products exhibit intense fluorescence in the solid state.