The dearomatization of arenes represents a powerful synthetic methodology to provide three-dimensional chemicals of high added value. Here we report a general and practical protocol for regioselective dearomative annulation of indole and benzofuran derivatives in an electrochemical way. Under undivided electrolytic conditions, a series of highly functionalized five to eight-membered heterocycle-2,3-fused indolines and dihydrobenzofurans, which are typically unattainable under thermal conditions, can be successfully accessed in high yield with excellent regio-and stereo-selectivity. This transformation can also tolerate a wide range of functional groups and achieve good efficiency in large-scale synthesis under oxidant-free conditions. In addition, cyclic voltammetry, electron paramagnetic resonance (EPR) and kinetic studies indicate that the dehydrogenative dearomatization annulations arise from the anodic oxidation of indole into indole radical cation, and this process is the ratedetermining step.
An electrochemical dehydrogenative C−H/N−H cross coupling of imidazopyridines with diarylamines has been developed. A variety of triarylamine derivatives could be obtained in high regioselectivities and moderate‐to‐good yields. In this transformation, the reaction is conducted in a simple undivided cell without using a metal catalyst or a stoichiometric amount of external chemical oxidants. Mechanistic studies indicate that the C−N bond is likely to be formed through the cross coupling between an arene cation radical and a nitrogen radical.
In this protocol, a wide range of substituted hexahydropyrroloindolines/tetrahydrofuroindolines are obtained with halide ion in high efficiencies, and neither external chemical oxidants nor harsh conditions are needed.
Medium-sized nitrogen heterocycles are prevalent motifs in many kinds of bioactive molecules and natural products. Owing to the unfavorable enthalpic and entropic barriers during the transition states, access to medium-sized rings is challenging. Herein, a general and practical electrochemical ringexpansion protocol has been developed from commercially available benzocyclic ketones and amides. In this regard, a series of highly functionalized eightto eleven-membered lactams could be successfully accessed in high yields and efficiencies. Notably, this transformation features excellent tolerance toward different electronic substituents of benzocyclic ketone and aniline moieties. Furthermore, satisfactory yields for gram-scale and direct one-pot synthesis, as well as the esterification of inert benzylic C-H bond, are additional advantages. Mechanistic studies indicate that this electrochemical dehydrogenative ring expansion proceeds through a unique remote amidyl radical migration-induced C-C bond cleavage and subsequent single-electron oxidation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.