Visible Light Photocatalysis for
[2+2] Cycloadditions

Significance

The present work was inspired by Krische and co-workers who demonstrated that cobalt- and copper-catalyzed [2+2] cycloadditions of bis(enones) are initiated by one-electron reduction of the enone (J. Am. Chem. Soc. 2001, 123, 6716). The authors report that irradiation of Ru(bipy)₃ ^²+ by visible light effectively catalyzes the [2+2] cycloaddition of a wide array of acyclic and cyclic bis(enones) under ambient conditions in short reaction times. The presence of at least one aryl enone is requisite as aliphatic enones and enoates have more negative reduction potentials and the corresponding radical anion cannot be generated under the reaction conditions.