Selectively Axing Halogens With Light

If you're having trouble removing a halogen atom from a highly functionalized intermediate, a trip to Home Depot might be in order. Jagan M. R. Narayanam, Joseph W. Tucker, and Corey R. J. Stephenson of Boston University have harnessed the energy from a store-bought 14-W fluorescent bulb to selectively remove halogens from complex substrates without disturbing sensitive functional groups such as hydroxyls, olefins, and alkynes (J. Am. Chem. Soc., DOI: 10.1021/ja9033582). Established dehalogenation reactions tend to have poor selectivity, rely on toxic tin reagents, or both. The new method employs a common ruthenium catalyst, Ru(bipyridyl)₃²⁺, to capture visible light energy from a lamp and introduce electrons into dehalogenations, such as the one shown. So far, the reaction requires a nearby functional group to activate the halogen, but the team hopes to tackle nonactivated halogens by tweaking the catalyst. Beyond dehalogenations, "one could easily imagine that this strategy could be used as a general method to initiate radical reactions," notes Tehshik P. Yoon of the University of Wisconsin, Madison, who has used a similar system for cycloaddition reactions.