Copper-Catalyzed 1,2-Addition of Nucleophilic Silicon to Aldehydes: Mechanistic Insight and Catalytic Systems

✍ Scribed by Dr. Christian Kleeberg; Evgenia Feldmann; Eduard Hartmann; Devendra J. Vyas; Prof. Dr. Martin Oestreich

• Book ID: 101838234
• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 303 KB
• Volume: 17
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.201102367

✦ Synopsis

Abstract

Activation of the SiB 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 NHCCuO__t__Bu 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 SiB 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 NHCCuO__t__Bu 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.