Visible-Light-Activated Catalytic Enantioselective β‑Alkylation of α,β-Unsaturated 2‑Acyl Imidazoles Using Hantzsch Esters as Radical Reservoirs

An efficient and practical method for the enantioselective β-functionalization of α,β-unsaturated 2-acyl imidazoles is described. The method uses a previously devised chiral-at-metal rhodium catalyst (Λ-RhS, 4 mol %) along with Hantzsch ester derivatives as alkyl radical sources. The rhodium complex exerts a dual role as the visible-light-absorbing unit upon substrate binding and as the asymmetric catalyst. The method provides up to quantitative yields with excellent enantioselectivities up to 98% ee and can be classified as a redox-neutral, electron-transfer-catalyzed reaction.