The first examples of Lewis base catalyzed enantioselective boron conjugate additions (BCAs) that afford products containing boron-substituted quaternary carbon stereogenic centers are presented. The carbon�boron bond forming reactions are performed in the presence of 1.0�5.0 mol % of a chiral N�hererocyclic carbene (NHC), which is generated in situ from a readily accessible C1�symmetric chiral imidazolinium salt, and commercially available bis(pinacolato)diboron [B2(pin)2]. Cyclic or linear a,ߖunsaturated ketones can be used as suitable substrates and the desired products are obtained in 63�95% yield and 91:9 to >99:1 enantiomeric ratio (e.r.). The utility of the NHC-catalyzed approach is demonstrated in the context of an enantioselective synthesis of antifungal natural product (-)�crassinervic acid.

Enantioselective synthesis of boron�substituted quaternary carbon stereogenic centers through NHC�catalyzed conjugate additions of (pinacolato)boron units to cyclic and acyclic enones

248th National Meeting (2014)

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