A Highly Efficient and Flexible Synthesis of Substituted Carbazoles by Rhodium-Catalyzed Inter- and Intramolecular Alkyne Cyclotrimerizations

An A→ABC or A→ABCD ring-formation strategy proves extremely efficient for generating substituted carbazoles ([Eq. (1)]; Ts=tosyl). Inter- and intramolecular alkyne cyclotrimerizations mediated by Wilkinson's catalyst provide substituted carbazoles of relevance for natural product and drug-related synthesis. The diynes required for these reactions are obtained in a few steps by a combination of Sonogashira and N-ethynylation reactions.