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.

The combined use of reaction kinetic analysis, ultrafast spectroscopy, and stoichiometric organometallic studies has enabled the elucidation of the mechanistic underpinnings to a photocatalytic C−N cross-coupling reaction. Steady-state and ultrafast spectroscopic techniques were used to track the excitedstate evolution of the employed iridium photocatalyst, determine the resting states of both iridium and nickel catalysts, and uncover the photochemical mechanism for reductive activation of the nickel cocatalyst. Stoichiometric organometallic studies along with a comprehensive kinetic study of the reaction, including rate−driving force analysis, unveiled the crucial role of photocatalysis in both initiating and sustaining a Ni(I)/Ni(III) cross-coupling mechanism. The insights gleaned from this study further enabled the discovery of a new photocatalyst providing a >30-fold rate increase.

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Herein we report a highly meta-selective C-H arylation using simple tertiary amines as the directing group. This method takes advantage of Pd/norbornene catalysis, offering a distinct strategy to control the site selectivity. The reaction was promoted by commercially available AsPh3 as the ligand and a unique "acetate cocktail". Aryl iodides with an ortho electron-withdrawing group were employed as the coupling partner. A wide range of functional groups, including some heteroarenes, are tolerated under the reaction conditions. In addition, the amine directing group can be easily installed and transformed to other common versatile functional groups. We expect this C-H functionalization mode to have broad implications for developing other meta-selective transformations beyond this work.

A Pd and norbornene-catalyzed ortho-arene amination via Catellani-type C-H functionalization is reported. Aryl halides are used as substrates; N-benzoyloxyamines and isopropanol are employed as the amine source (oxidant) and reductant respectively. Examples are provided in 50-99% yields with high functional group tolerance. This method gives complementary site selectivity at the ortho- instead of ipso-position of aryl halides.