Photocatalysis of intermolecular [2+2] cycloadditions of acyclic enones using visible light irradiation

ORGN 689

Juana Du, and Tehshik P. Yoon, Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, WI 53706
We demonstrate that Ru(bpy)3Cl2 is an efficient visible light photocatalyst for the formal [2+2] intermolecular cycloaddition of enones. Dimerization of aryl enones is achieved with good yields and diastereoselectivity. While one aryl enone is a strict requirement, a variety of Michael acceptors participate readily as reaction partners to favor the crossed cyclobutane products. We propose a mechanism in which a photogenerated Ru(bpy)3+ complex promotes one-electron reduction of the enone substrate, which undergoes subsequent radical anion cycloaddition.