Intra- and intermolecular reactions of indoles with alkynes catalyzed by gold |
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Authors: | Ferrer Catalina Amijs Catelijne H M Echavarren Antonio M |
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Affiliation: | Institute of Chemical Research of Catalonia (ICIQ), Av. Pa?sos Catalans 16, 43007 Tarragona, Spain, Fax: (+34)?977‐920‐225 |
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Abstract: | Indoles react intramolecularly with alkynes in the presence of gold catalysts to give from six- to eight-membered-ring annulated compounds. The cationic Au(I) complex [Au(P{C(6)H(4)(o-Ph)}(tBu)(2))(NCMe)]SbF(6) 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 AuCl(3) 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. |
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Keywords: | alkynes allenes cyclization gold homogeneous catalysis indoles |
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