[2+2] Cycloadditions by Visible Light Photocatalysis

Significance

Previously, the authors have reported intramolecular [2+2] cycloadditions of symmetric aryl enones under visible light photo­catalysis (J. Am. Chem. Soc. 2008, 130, 12886). In the present work, the intermolecular [2+2] cycloaddition reaction of aryl enones with various Michael acceptors is described. Importantly, the acceptor must be more reactive than an aryl enone to minimize homodimerization, yet be less susceptible to one-electron reduction by the photocatalyst. Further, the reaction is initiated by photoexcitation of Ru(bipy)₃Cl₂ and does not involve electronically excited states of the enone.