palladium-catalyzed oxidative coupling reactions of N-substituted indoles or their carboxylic acid derivatives with alkynes. Unsymmetrically 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
The palladium-catalyzedoxidative coupling of indole-3-carboxylic acids with alkynes effectively proceeds in a 1:2 manner accompanied by decarboxylation to produce the corresponding 1,2,3,4-tetrasubstituted carbazoles, some of which exhibit solid-state fluorescence. Pyrrole-, benzofuran-, and furancarboxylic acids also undergo the decarboxylative coupling to afford highly substituted indole, dibenzofuran