Transition metal-catalysed couplings between arenes and strained or reactive rings: combination of C–H activation and ring scission
Organic transformations that involve direct functionalization of C–H bonds represent an attractive synthetic strategy that maximizes atom- and step-economy. With the generally high stability of C–H bonds, these processes have mostly required harsh reaction conditions, in combination with the necessity of activation of the C–H substrates and/or the coupling partners. As a class of activated coupling partners, strained or reactive rings exhibited high activity in the coupling with aryl and alkyl C–H bonds. Such a high reactivity of the rings allowed the facile construction of various new structural platforms via coupling with scission of the ring structures. The combination of C–H activation and scission of the rings allowed for applications of a broader scope of C–H bonds, including those less reactive alkyl ones. This synthetic diversity of these rings has been realized owing to the intrinsically different mechanisms of the interactions of transition metal catalysts and the strained/reactive rings.