Visible light photocatalysis of intramolecular radical cation Diels-Alder cycloadditions.

Intramolecular radical cation Diels-Alder reactions can be conducted under photocatalytic conditions using visible light irradiation. The photocatalyst system involves the use of a Ru(bpy)(3) (2+) chromophore and methyl viologen as a co-oxidant. These reactions enable the cycloaddition of substrates whose thermal Diels-Alder cycloadditions are electronically mismatched and thus require forcing conditions. Nevertheless, the radical cation cycloadditions can be conducted on gram scale using ambient sunlight as the only source of irradiation.