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Synfacts 2009(11): 1197-1197  
DOI: 10.1055/s-0029-1218141
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of Indoloazocine by Hg(OTf)2-Catalyzed Intramolecular Carbocyclization

Contributor(s): Victor Snieckus, Cédric Schneider
P. A. Donets, K. van Hecke, L. van Meervelt, E. V. van der Eycken*
Katholieke Universiteit Leuven, Belgium
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Publication History

Publication Date:
22 October 2009 (online)

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Significance

Reported is the synthesis of indoloazocinones 2 or 5 via a microwave-assisted protocol based on an Hg(OTf)2-catalyzed intramolecular alkyne carbocyclization reaction of amides 1 and 4 to products 2 and 5, respectively. A screening of Brønsted acids (CF3CO2H and TfOH) and Lewis acids showed that the product is formed only when using Hg(OTf)2. Optimized conditions include the use of CH2Cl2 as solvent and microwave-assisted heating (decreased reaction time). Several limitations on the structure of amides 1 were discovered in particular when R² = H, and R³ is very bulky (e.g., R³ = t-Bu), when R³ = H and when R¹ = EWG. Moreover, in order to expand the scope of the reaction, the tryptamine part was varied (e.g., 4, l-tryptophan derivatives). Finally, the hydrogenation of the conjugated double bond in 5 and amide group in a derivative of 2 were also described.