Sequential, domino and tandem reactions could be defined as a sequence of synthetic transformations that occur one after the other, in the same reaction flask. This Review highlights recent advances at the overlap of two worlds: transition-metal mediated C-H activation as a trigger of cascade reaction, for the heterocycles synthesis. To shed some light on this intricate "middle-earth", focus was put on the reaction mechanism rather than the type of metal or the chronological order of the reaction. The aim is to separate, and then highlight, the true domino reactions initiated by C-H activation, compared to other examples of C-H functionalization for heterocycle syntheses.
Ready availability, low cost and low toxicity of cobalt salts have redirected the attention of researchers away from noble metals, such as Pd, Rh, and Ir, towards Co in the field of C-H functionalization. In this context, the examples of Co-catalysed functionalization have exponentially grown over the last few decades. This present review focuses on the most recent developments on Co-catalysed C(sp2)-H and C(sp3)-H functionalizations. Included is also a comprehensive overview of enantioselective transformations.
Unactivated olefins usually react poorly in conventional alkenylation reactions. Their introduction via C-H activation is limited to aromatic acids. Herein, we disclose a C-H functionalization protocol of aromatic amines with unactivated olefins, which shows exclusive allylic selectivity for the distal ring of the biphenyl system by exploiting a readily available cobalt(II) catalyst. The allylation proceeds smoothly involving a broad set of unbiased olefins and biaryls, giving access to the functionalization of the biphenyl scaffold.
