Chemistry

Telling O Where to Go

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Science  04 Oct 2013:
Vol. 342, Issue 6154, pp. 15
DOI: 10.1126/science.342.6154.15-b
CREDIT: M. CHRISTINA WHITE

The abundance of aliphatic C-H bonds in organic molecules poses an enticing, yet maddening challenge to synthetic chemists. On the one hand, direct oxidation protocols are prospectively applicable to an immense range of substrates; on the other hand, genuinely useful methods must achieve selectivity among numerous sites in a given substrate that differ only subtly. Gormisky and White tackle this challenge through the use of a pair of complementary ligands on an iron catalyst that activates peroxide for C-H oxidation. Elaborating on a previously reported ligand, they introduce bulky bis(trifluoromethyl) phenyl groups that roughly halve the conical angle-bounding substrate approach to the metal center. As a result, this bulkier catalyst favors oxidation at sterically unhindered sites on a substrate, whereas the previous catalyst manifested selectivity governed by the substrate's inherent reactivity. The authors develop a predictive model for the site preferences of each ligand based on steric and electronic factors, and they validate it through site-selective oxidations of such complex molecules as artemisinin (where they can select between two of nine possible sites) and the pentacyclic triacetoxytricalysiolide.

J. Am. Chem. Soc. 135, 10.1021/ja407388y (2013).

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