Olefinic C–H functionalization represents an atom- and step economic approach to valuable olefin derivatives from simpler ones, but controlling the selectivity remains a challenge. Remarkable progress has been made in the site-selective C–H functionalization of arenes and alkanes, but there are still limited examples of selective C–H functionalization of olefins presumably due to the lability and easy decomposition of the alkenyl moiety. Chelation-assisted C–H activation represents an efficient protocol for site- and stereo-selective construction of carbon–carbon and carbon–heteroatom bonds. This review highlights recent advances in vicinal- and geminal-group-directed olefinic C–H functionalization, including alkenylation, arylation, alkynylation, alkylation, halogenation, silylation, cyanation and annulation by the formation of exo-/endo-metallocycles. In particular, geminal-group-directed C–H functionalization is covered for the first time, as well as distal-selective alkenyl C–H functionalization under palladium/norbornene cooperative catalysis, which provides novel disconnections in retrosynthetic analysis and represents the future trend in green chemistry.

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 oxidant-free cross-coupling reaction of electron-deficient alkenes using an inexpensive ruthenium catalyst is reported. With the assistance of the oxidizing directing group CONH(OMe), this protocol provides a mild, straightforward and efficient method for the preparation of valuable 1,3-butadiene skeletons with excellent Z,E selectivities.

Cross-coupling reactions of enol carbamates with alkynes or alkenes are reported, using an inexpensive ruthenium catalyst. With the assistance of the directing group OCONMe₂, the protocols provide mild, stereo-selective and efficient routes for the preparation of valuable (Z,Z) and (Z,E)-butadiene skeletons.