Geminal group-directed olefinic C-H functionalization via four- to eight-membered exo-metallocycles.

Abstract

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.