Intra- and Intermolecular Reactions of Indoles with Alkynes Catalyzed by Gold

• Published in: Chemistry : a European journal 2007-01, Vol.13 (5), p.1358-1373
• Main Authors: Ferrer, Catalina, Amijs, Catelijne H. M., Echavarren, Antonio M.
• Format: Article
• Language: English
• Subjects: alkynes; allenes; cyclization; gold; homogeneous catalysis; indoles
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200601324

Indoles react intramolecularly with alkynes in the presence of gold catalysts to give from six‐ to eight‐membered‐ring annulated compounds. The cationic AuI complex [Au(P{C6H4(o‐Ph)}(tBu)2)(NCMe)]SbF6 is the best catalyst for the formation of six‐ and seven‐membered rings by 6‐endo‐dig, 6‐exo‐dig, and 7‐exo‐dig cyclizations. Indoloazocines are selectively obtained with AuCl3 as catalyst in a rare 8‐endo‐dig process. In this process allenes or tetracyclic annulated derivatives are also formed as a result of an initial fragmentation reaction. The intermolecular reaction of indoles with alkynes proceeds to form 3‐alkenylated intermediates that react with a second equivalent of indole to give bisindolyl derivatives. Indoles that are substituted at the 3‐position react intermolecularly with alkynes to give 2‐alkenylated intermediates that can be trapped intramolecularly with the appropriate nucleophiles. The golden touch: Indoles react intramolecularly with alkynes in the presence of gold catalysts to give from six‐ to eight‐membered ring annulated compounds. The intermolecular reaction of indoles with alkynes proceeds to form 3‐alkenylated intermediates that react with a second equivalent of indole to give bisindolyl derivatives (see scheme).