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.

Electrochemical oxidative [4 + 2] annulation for the synthesis of pyrazines.