Organocatalytic dimensions to the C–H functionalization of the carbocyclic core in indoles: a review update

An integration of two dynamic research paradigms - organocatalysis and remote C-H bond functionalization - has emerged as a profound competitor to conventional transition-metal catalyzed processes. In the contemporary research world of ample metal mediated transformations, there is a unique space for organocatalytic functionalization techniques. The benzene core in indoles remains difficult to explore owing to the dominant reactivity of the pyrrole core. Yet, exciting developments have been achieved to access remote regioselectivities: the C4, C5, C6 and C7 positions. This review documents contributions devoted to the metal-free organocatalytic functionalization of indoles in the carbocyclic ring positions up to the middle of 2020.