Azepinoindole Synthesis via a <i>N</i>‑Bromosuccinimide-Induced Cycloisomerization of Enaminoester/Enaminone

A protocol based on a newly developed N-bromosuccinimide (NBS)-induced cycloisomerization was described to prepare tricyclic azepino­[4,5-b]­indoles from simple β-enaminoesters or β-enaminones containing an indole unit. A mechanism involving a Pictet–Spengler cyclization, an aziridine ring formation, and a regioselective C–N bond cleavage was proposed to account for the medium-sized ring formation and the migration of electron-withdrawing group (ester, ketone).