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  • Title: Site- and enantioselective formation of allene-bearing tertiary or quaternary carbon stereogenic centers through NHC-Cu-catalyzed allylic substitution.
    Author: Jung B, Hoveyda AH.
    Journal: J Am Chem Soc; 2012 Jan 25; 134(3):1490-3. PubMed ID: 22214185.
    Abstract:
    Catalytic enantioselective allylic substitutions that result in addition of an allenyl group (<2% propargyl addition) and formation of tertiary or quaternary C-C bonds are described. Commercially available allenylboronic acid pinacol ester is used. Reactions are promoted by a 5.0-10 mol % loading of sulfonate-bearing chiral bidentate N-heterocyclic carbene (NHC) complexes of copper, which exhibit the unique ability to furnish chiral products arising from the S(N)2' mode of addition. Allenyl-containing products are generated in up to 95% yield, >98% S(N)2' selectivity, and 99:1 enantiomeric ratio (er). Site-selective NHC-Cu-catalyzed hydroboration of enantiomerically enriched allenes and conversion to the corresponding β-vinyl ketones demonstrates the method's utility.
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