[2+2] cycloadditions by oxidative visible light photocatalysis.

Photochemical reactions are remarkable for their ability to easily assemble cyclobutanes and other strained ring systems that are difficult to construct using other conventional synthetic methods. We have previously shown that Ru(bpy)(3)(2+) is an efficient photocatalyst that promotes the [2+2] cycloadditions of electron-deficient olefins with visible light. Here, we show that Ru(bpy)(3)(2+) is also an effective photocatalyst for the [2+2] cycloaddition of electron-rich olefins. This transformation is enabled by the versatile photoelectrochemical properties of Ru(bpy)(3)(2+), which enables either one-electron reduction or one-electron oxidation of interesting organic substrates under appropriate conditions.