Copper‐Catalyzed 1,2‐Addition of Nucleophilic Silicon to Aldehydes: Mechanistic Insight and Catalytic Systems
- 24 October 2011
- journal article
- research article
- Published by Wiley in Chemistry – A European Journal
- Vol. 17 (48) , 13538-13543
Abstract
Activation of the SiB inter‐element bond with copper(I) alkoxides produces copper‐based silicon nucleophiles that react readily with aldehydes to yield α‐silyl alcohols (that is, α‐hydroxysilanes) after hydrolysis. Two independent protocols were developed, one employing a well‐defined NHCCuOtBu complex and one using the simple CuCN–NaOMe 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 SiB reagent and the aldehyde (a boric acid ester of the α‐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 NHCCuOtBu catalytic setup performs nicely at elevated temperature. A more reactive catalytic system is generated from CuCN–NaOMe, showing fast turnover at a significantly lower temperature. Both aromatic and aliphatic aldehydes are transformed into the corresponding α‐silyl alcohols in good to very good yields under these mild reaction conditions.Keywords
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