A Practical Method for Enantioselective Synthesis of All-Carbon Quaternary Stereogenic Centers through NHC-Cu-Catalyzed Conjugate Additions of Alkyl- and Arylzinc Reagents to β-Substituted Cyclic Enones

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Abstract
We present the first examples of Cu-catalyzed enantioselective conjugate additions of alkyl- and arylzinc reagents to unactivated cyclic β-substituted enones. Transformations are promoted in the presence of 2.5−15 mol % of a readily available chiral NHC-based Cu complex, affording the desired products bearing all-carbon quaternary stereogenic centers in 67→98% yield and in up to 97% ee. Catalytic enantioselective reactions can be carried out on a benchtop, with undistilled solvent and commercially available (not further purified) Cu salts. Mechanistic models, accounting for the observed levels and trends in enantioselectivity are provided.

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