Photoiodocarboxylation of Activated C═C Double Bonds with CO2 and Lithium Iodide.

The photolysis at 254 nm of lithium iodide and olefins 1 carrying an electron-withdrawing Z-substituent in CO2-saturated (1 bar) anhydrous acetonitrile at room temperature produces the atom efficient and transition metal-free photoiodocarboxylation of the C═C double bond. The reaction proceeds well for terminal olefins 1 to form the new C-I and C-C σ-bonds at the α and β-positions of the Z-substituent, respectively, and is strongly inhibited by polar protic solvents or additives. The experimental results suggest that the reaction channels through the radical anion [CO2•-] in acetonitrile, yet involves different intermediates in aqueous medium. The stabilizing ion-quadrupole and electron donor-acceptor interactions of CO2 with the iodide anion play a crucial role in the reaction course as they allow CO2 to penetrate the solvation shell of the anion in acetonitrile, but not in water. The reaction paths and the reactive intermediates involved under different conditions are discussed.