Formation of Vinyl-, Vinylhalide- or Acyl-Substituted Quaternary Carbon Stereogenic Centers through NHC−Cu-Catalyzed Enantioselective Conjugate Additions of Si-Containing Vinylaluminums to β-Substituted Cyclic Enones
- 20 December 2010
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 133 (4), 736-739
- https://doi.org/10.1021/ja110054q
Abstract
A catalytic method for enantioselective conjugate addition (ECA) of Si-containing vinylaluminum reagents to β-substituted cyclopentenones and cyclohexenones is described. Reactions are promoted by 1.0−5.0 mol % of a bidentate NHC−Cu complex, which is prepared from air-stable CuCl2•2H2O and used in situ, and typically proceed to completion within 15−20 min. The requisite vinylmetals are generated efficiently by a site-selective hydroalumination of an alkyne with dibal-H. The desired products, containing a quaternary carbon stereogenic center, are obtained in 48−95% yield after purification and in 89:11 to >98:2 enantiomer ratio (er). The vinylsilane moiety within the products can be functionalized to afford acyl, vinyliodide, or desilylated alkenes in 67% to >98% yield and with >90% retention of the alkene’s stereochemical identity. The utility of the catalytic process is illustrated in the context of a concise enantioselective synthesis of riccardiphenol B.Keywords
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