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 functionalisation.

Sequential,d omino and tandem reactions could be defined as as equence of synthetic transformationst hat occur one after the other,i nt he same reaction flask. This Review highlights recent advances at the overlap of two worlds:t ransition-metal mediated CÀHa ctivation as at rigger of cascade reaction, for the heterocycles synthesis. To shed some light on this intricate "middle-earth",f ocus was put on the reactionm echanismr ather than the typeo f metal or the chronologicalo rder of the reaction. The aim is to separate, and then highlight, the true domino reactions initiatedb yC ÀHa ctivation, compared to other examples of CÀHf unctionalization for heterocycle syntheses.

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.

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 on the transition‐metal‐mediated C−H activation as a trigger of cascade reactions for the synthesis of heterocycles. To shed some light on this research area at the intersection of two fields, focus was put on the reaction mechanism rather than on the type of metal or the chronological order of the reaction. The aim is to separate and highlight the true domino reactions initiated by C−H activation, compared to other examples of C−H functionalization for heterocycle synthesis. For more details see the Review by D. Maiti, G. Zanoni et al. on page 9749 ff.