Adding Functionality To Aliphatics

Chemists can’t do much with the C–H bonds in aliphatic compounds. They tend to sit there just taking up space. This year, researchers figured out a way to turn these mundane C–H bonds in alcohols or ketones into useful C–OH moieties, creating 1,3-diols—molecular motifs found in polymers, pharmaceuticals, and natural products (C&EN, March 5, page 8; Nature, DOI: 10.1038/nature10785).The reaction, developed by University of California, Berkeley, chemists John F. Hartwig and Eric M. Simmons, makes use of an iridium catalyst and the oxygen atom that’s already in the molecule. Selectively functionalizing a single, unactivated C–H bond in a molecule that’s full of them presents a considerable challenge for synthetic chemists because the difference in reactivity between such bonds is subtle. Hartwig and Simmons realized they could make an unreactive primary alkyl group into a reactive site if they counted on a nearby oxygen atom as a guide. They used diethyl silane to transform an alcohol or ketone precisely three carbons away from the primary C–H bond to a silyl ether. In the presence of an iridium phenan­throline catalyst, the silicon atom reaches across the three carbons and displaces hydrogen to form a five-membered ring. Subsequent oxidation turns the molecule into a 1,3-diol. The reaction selectively functionalizes only the primary C–H bond three carbon atoms away from the oxygen guide, even when there are more reactive C–H bonds in the molecule.