Ni(I)-Catalyzed β,δ-Vinylarylation of γ,δ-Alkenyl α‑Cyanocarboxylic Esters via Contraction of Transient Nickellacycles

We
disclose a transmetalation-initiated Ni­(I)-catalyzed regioselective
β,δ-vinylarylation of γ,δ-alkenyl α-cyanocarboxylic
esters with vinyl triflates and arylzinc reagents. This reaction proceeds
via contraction of six-membered nickellacycles to five-membered nickellacycles
to form carbon–carbon bonds at the nonclassical homovicinal
sites, and it provides expeditious access to a wide range of complex
aliphatic α-cyanoesters, α-cyanocarboxylic acids, dicarboxylic
acids, dicarboxylic acid monoamides, monocarboxylic acids, nitriles,
and spirolactones. Control, deuterium labeling, and crossover experiments
indicate that (i) the nickellacycle contraction occurs by β-H
elimination, followed by hydronickellation on transiently formed alkenes,
and (ii) the Ni species are stabilized as Ni-enolates.