Divergent Asymmetric Dialkylation of Dienoic Acids with Carbonyls and Zinc Reagents via Tandem Ni(0) and Ni(II) Catalysis

Reductive elimination of dialkyl Ni(II) species for the enantioselective construction of a C(sp 3 )–C(sp 3 ) bond represents a fundamental challenge due to the low oxidative ability of the Ni(II) ion. Here we report that a Ni(0) complex can perform as a π-Lewis base to activate the 2,4-dienoic carboxylate salts formed in situ with zinc reagents, such as dimethylzinc, and undergo vinylogous addition to carbonyls α-regioselectively and stereoselectively. After transmetalation with another organometallic reagent, the resultant alkyl allylic nickel(II) species readily undertake reductive elimination to finally forge two C(sp 3 )–C(sp 3 ) bonds, even with switchable diastereodivergence and α,β- or α,δ-regiodivergence via ligand or substrate control. A self-assembled dinuclear Zn cage framework is believed to enhance the latter process through an intriguing outer-sphere π-acidic activation mode.