Isolation and Structural Characterization of Se‐Hügerschoff Intermediates Derived From 4‐Bromoaniline

ABSTRACT A brominated intermediate within the Hügerschoff reaction has long been postulated but never directly observed. Herein, we isolate and characterize Se‐brominated Hügerschoff intermediates formed during the seleno‐Hügerschoff reaction of arylselenoureas. Using X‐ray crystallography, we established their structures, and using Density Functional Theory ( DFT ) analysis, we studied their role in the intramolecular Hügerschoff cyclization to 2‐aminobenzoselenazoles. The isolation of such Hügerschoff intermediates provides both mechanistic clarity and a practical framework towards improving the reliability of seleno‐Hügerschoff chemistry.