Desymmetrization of Cyclohexadienones Containing a Quaternary γ-Carbon Atom by Conjugate Addition of Boron Nucleophiles

Abstract

A highly enantio-and diastereoselective copper-catalyzed conjugate monoborylation of γ,γ-disubstituted cyclohexadienone derivatives is reported. Two contiguous stereocenters are generated in this groupselective reaction, one at the formed boron-bearing carbon atom in a neopentylic position and one at the quaternary carbon atom. A subsequent 1,4-addition of a boron nucleophile to the remaining α,β-unsaturated acceptor allows for the construction of another stereocenter in the other neopentylic position, thereby leading to three adjacent stereogenic carbon atoms in a highly congested environment. The diastereoselectivity of that second borylation can be controlled by different chiral ligands to selectively afford either the syn-or the anti-1,3-diborylated product.