Radical Cation Diels–Alder Cycloadditions by Visible Light Photocatalysis

Ruthenium(II) polypyridyl complexes promote the efficient radical cation Diels-Alder cycloaddition of electron-rich dienophiles upon irradiation with visible light. These reactions enable facile 4 + 2 cycloadditions that would be electronically mismatched under thermal conditions. Key to the success of this methodology is the availability of ligand-modified ruthenium complexes that enable rational tuning of the electrochemical properties of the catalyst without significantly perturbing the overall photophysical properties of the system.