This review highlights recent advances in vicinal- and geminal-group-directed alkenyl C–H functionalizations which proceeded by endo- and exo-cyclometallation.

The first cobalt-catalyzed cross-couplings between olefins has been demonstrated to provide C­(alkenyl)–H alkenylation and alkylation products, using complex [Cp*Co­(CO)­I2]. While coupling partner acrylates afforded conjugated dienoates, α,β-unsaturated ketones led to γ-alkenyl ketones completely, representing a switchable C–H functionalization controlled by different carbonyl groups.

Great efforts have been made in the activation of a C(alkenyl)-H bond vicinal to the directing group to proceed via five- or six-membered endo-metallocycles. In stark contrast, functionalization of a C(alkenyl)-H bond geminal to the directing group via exo-metallocycle pathway continued to be elusive. Here we report the selective transformation of an olefinic C-H bond that is geminal to the directing group bearing valuable hydroxyl, carbamate or amide into a C-C bond, which proceeds through four- to eight-membered exo-palladacycles. Compared to the reported mechanisms proceeding only through six-membered exo-palladacycles via N,N-bidentate chelation, our weak and O-monodentate chelation-assisted C(alkenyl)-H activations tolerate longer or shorter distances between the olefinic C-H bonds and the coordinating groups, allowing for the functionalizations of many olefinic C-H bonds in alkenyl alcohols, carbamates and amides. The synthetic applicability has been demonstrated by the preparative scale and late-stage C-H functionalization of steroid and ricinoleate derivatives.

An asymmetric α-C–H alkenylation of aryl alkenes has been disclosed to provide axially chiral aryl 1,3-dienes, proceeding through six-membered exo-cyclopalladation, assisted by an aldehyde/l-t-leucine derived transient chiral auxiliary.

We report on N,N-bidentate-chelation-assisted α- and β-olefinic C-H alkenylation of aryl alkenes in ethanol to afford aryl dienes/trienes with excellent regio- and stereo-selectivities. The reaction of 2-alkenyl benzylamine and benzoic...