Photocatalysis With Visible Light

To marshal their reagents into action, chemists often turn to the energizing power of light. Most organic compounds, however, only react when they absorb high-frequency ultraviolet light, and the specialized photoreactors needed for such syntheses allow only a few photocatalytic reactions to make it beyond the lab to large-scale operations. Recently, chemists have turned to the popular ruthenium bipyridine complex, Ru(bpy)₃²⁺, to harness energy from lower energy visible wavelengths and inject electrons into reactions with organic molecules (C&EN, Sept. 8, page 10). Tehshik P. Yoon of the University of Wisconsin, Madison, and coworkers have now applied this strategy to [2+2] cycloadditions of enones (J. Am. Chem. Soc., DOI: 10.1021/ja805387f). The researchers found they could get aryl bis(enones) to undergo intramolecular cyclization (shown) with Ru(bpy)₃²⁺, a few key additives, and a standard floodlight. The reaction proceeds in good yield, with excellent diastereoselectivity. An intermolecular dimerization of untethered aryl enones also worked well. "This approach to effecting visible light photocatalysis has enormous potential for the development of new reaction protocols with reduced environmental impact," the researchers note.