Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 17, Issue 48, Pages 13538-13543Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201102367
Keywords
aldehydes; copper; nucleophilic addition; silicon; transmetalation; X-ray diffraction
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Funding
- Fonds der Chemischen Industrie
- Deutsche Forschungsgemeinschaft [Oe 249/3-2]
- NRW Graduate School of Chemistry
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Activation of the Si-B inter-element bond with copper(I) alkoxides produces copper-based silicon nucleophiles that react readily with aldehydes to yield a-silyl alcohols (that is, a-hydroxysilanes) after hydrolysis. Two independent protocols were developed, one employing a well-defined NHC-CuOtBu complex and one using the simple CuCNNaOMe combination without added ligand. The mechanism of the aldehyde addition was investigated in detail by stoichiometric and catalytic experiments as well as NMR spectroscopic measurements. The primary reaction product of the addition of the Si-B reagent and the aldehyde (a boric acid ester of the a-silyl alcohol) and also the dead-end intermediate, formed in the competing [1,2]-Brook rearrangement, were characterized crystallographically. Based on these data, a reasonable catalytic cycle is proposed. The NHC-CuOtBu catalytic setup performs nicely at elevated temperature. A more reactive catalytic system is generated from CuCNNaOMe, showing fast turnover at a significantly lower temperature. Both aromatic and aliphatic aldehydes are transformed into the corresponding a-silyl alcohols in good to very good yields under these mild reaction conditions.
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