Alkylation reactions represent an important organic transformation to form C-C bonds. In addition to conventional approaches with alkyl halides or sulfonates as alkylating agents, the use of unactivated olefins for alkylations has become attractive from both cost and sustainability viewpoints. This Review summarizes transition-metal-catalyzed alkylations of various carbon-hydrogen bonds (addition of C-H bonds across olefins) using regular olefins or 1,3-dienes up to May 2016. According to the mode of activation, the Review is divided into two sections: alkylation via C-H activation and alkylation via olefin activation.

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We describe a Pd-catalyzed site-selective functionalization of unactivated aliphatic C-H bonds, providing chemically differentiated 1,2-diols from monoalcohol derivatives. The oxime was employed as both a directing group (DG) and an alcohol surrogate for this transformation. As demonstrated in a range of substrates, the C-H bonds β to the oxime group are selectively oxidized. Besides activation of the methyl groups, methylene groups (CH(2)) in cyclic substrates and methine groups (CH) at bridge-head positions can also be functionalized. In addition, an intriguing oxidative skeleton rearrangement was observed using the menthol-derived substrate. The use of exo-directing groups in C-H activation, as illustrated in this work, would potentially open doors for the discovery of new transformations and new cleavable DGs.

Site-selective C-H functionalization has emerged as an attractive tool for derivatizing complex synthetic intermediates, but its use for late-stage diversification is limited by the functional groups that can be introduced, especially at unactivated sp(3)-hybridized positions. To overcome this, we introduce a strategy that directly installs a sulfonyloxy group at a β-C-H bond of a masked alcohol and subsequently employs nucleophilic substitution reactions to prepare various derivatives. Hydroxyl groups are widely found in bioactive molecules and are thus readily available as synthetic handles. A directing group is easily added (and subsequently removed) from the alcohols such that a formal site-selective β-C-H sulfonyloxylation of these alcohols is achieved. Substitution reactions with carbon, nitrogen, oxygen and other nucleophiles then lead to diverse functionalizations that may help to streamline the synthesis of complex analogues for drug discovery.

Three types of dirhodium tetrakis­(tri­aryl­cy­clo­pro­pane­car­boxy­late) complexes were generated and shown to adopt disparate high-symmetry structures. These catalysts were evaluated in the intermolecular C–H functionalization of an array of terminally substituted n-alkanes and displayed various site-selectivity as a function of catalyst and substrate structure, which could be correlated through quantitative relationships.