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DOI: 10.1055/s-2008-1042702
Asymmetric Ruthenium-Mediated Propargylation of Indoles
Contributor(s):Mark Lautens, Frédéric MénardThe University of Tokyo, Japan
Remarkable Effect of N-Substituent on Enantioselective Ruthenium-Catalyzed Propargylation of Indoles with Propargylic Alcohols
Org. Lett. 2007, 9: 5561-5564
Publication History
Publication Date:
21 February 2008 (online)
Key words
ruthenium - indoles - propargylation - sulfur ligands
Significance
The above reaction with indoles represents an extension of Nishibayashi’s earlier report for the nucleophilic attack of furans and anilines (Synfacts 2007, 1170). Though a number of methods exist for the propargylation of indoles with Brønsted or Lewis acids, none were reported to be asymmetric. The dimeric ruthenium-thiolate complex is prepared in situ and accomplishes the asymmetric Friedel-Crafts-type alkylation to afford 1,1-disubstituted, unprotected propynes in moderate to good yield and good enantioselectivity.
Review
M. Bandini, E. Emer, S. Tommasi, A. Umani-Ronchi Eur. J. Org. Chem. 2006, 3527.
Comment
The use of the free propargylic alcohol makes the method attractive for the synthesis of unsymmetrically substituted alkynes. The isomerization of the propargylic alcohol to the allenylidene-ruthenium species is supported by control experiments done in previous studies (Angew. Chem. Int. Ed. 2007, 46, 6488). Due to the limited number of examples, a clear trend in the electronic behavior of either reacting partner cannot be identified. The exact stereochemistry of the products obtained remains to be confirmed.