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DOI: 10.1055/s-2007-968406
Mukaiyama Aldol Reactions Catalyzed by N-Heterocyclic Carbenes
J. J. Song*, Z. Tan, J. T. Reeves, N. K. Yee, C. H. Senanayake
Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, USA
Publication History
Publication Date:
24 April 2007 (online)
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Significance
A highly efficient organocatalytic protocol for Mukaiyama aldol reactions of trimethylsilyl ketene acetals as well as trimethylsilyl enol ethers with various, mostly aromatic aldehydes is described. In the presence of only 0.5 mol% of bis(adamantyl)-substituted imidazol-2-ylidene, aldol products are obtained in moderate to high yields (25-91%). In addition, the activated ketone 2,2,2-trifluoroacetophenone was also found to undergo aldol reactions in high yields. The authors propose that the N-heterocyclic carbene (NHC) acts as a carbon-centered nucleophilic catalyst activating the Si-O bond of enoxysilanes through the formation of a pentavalent silicon complex. Furthermore, it was shown that NHCs show a better performance compared to commonly employed P- or N-centered Lewis base catalysts.