Transition-metal-catalyzed site-selective C7-functionalization of indoles: advancement and future prospects.

C7-Decorated indoles are important structural motifs present in a plethora of bioactive and pharmaceutical compounds. Early stage developments for C7 modifications were realized through directed metallation (DOM) and subsequent quenching with suitable electrophiles or by halogenation with Cu(ii) halides. Direct C-7 functionalization of indoles is comparatively difficult compared to functionalization at C-2 and C-3 positions owing to the inherent reactivity of the pyrrole-type ring. However, recently transition-metal-catalyzed auxiliary assisted site-selective C-7 functionalization of indoles has emerged as an elegant synthetic tool for carbon-carbon and carbon-heteroatom bond formation to diversify the indoles. This article covers the advancement, application and mechanistic underpinnings of the evolved transformations of the otherwise inert C7-H bond up to October 2018.