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The laboratory synthesis of complex organic molecules relies heavily on the introduction and manipulation of functional groups, such as carbon–oxygen or carbon–halogen bonds; carbon–hydrogen bonds are far less reactive and harder to functionalize selectively. The idea of C–H functionalization, in which C–H bonds are modified at will instead of the functional groups, represents a paradigm shift in the standard logic of organic synthesis1,2,3. For this approach to be generally useful, effective strategies for site-selective C–H functionalization need to be developed. The most practical solutions to the site-selectivity problem rely on either intramolecular reactions4or the use of directing groups within the substrate5,6,7,8. A challenging, but potentially more flexible approach, would be to use catalyst control to determine which site in a particular substrate would be functionalized9,10,11. Here we describe the use of dirhodium catalysts to achieve highly site-selective, diastereoselective and enantioselective C–H functionalization ofn-alkanes and terminally substitutedn-alkyl compounds. The reactions proceed in high yield, and functional groups such as halides, silanes and esters are compatible with this chemistry. These studies demonstrate that high site selectivity is possible in C–H functionalization reactions without the need for a directing or anchoring group present in the molecule.