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 beta-functionalization of alpha, beta-unsaturated 2-acyl imidazoles is described. The method uses a previously devised chiral-at-metal rhodium catalyst (Lambda-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.