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

A highly enantio- and diastereoselective copper-catalyzed conjugate monoborylation of γ,γ-disubstituted cyclohexadienone derivatives is reported. Two contiguous stereocenters are generated in this group-selective 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.

本文报道了一种兼具高对映选择性与非对映选择性的铜催化γ,γ-二取代环己二烯酮衍生物的共轭单硼化反应。该基团选择性反应可生成两个连续手性中心，其一位于新戊基位的含硼碳原子上，其二位于季碳原子上。后续通过硼亲核试剂对剩余α,β-不饱和受体的1,4-加成，可在另一新戊基位构建第三个手性中心，从而在高度拥挤的空间环境中得到三个相邻的手性碳原子。第二次硼化反应的非对映选择性可通过不同手性配体进行调控，以选择性地获得顺式（syn）或反式（anti）-1,3-二硼化产物。