Ring‐Opening Cyclization (ROC) of Aziridines With 2‐(2‐Bromophenyl)‐1 H ‐Benzimidazoles: Rotamer Analysis and Synthesis of Benzimidazole‐Fused 1,4‐Benzodiazepine

We report a novel strategy for the synthesis of benzimidazole‐fused 1,4‐benzodiazepine derivatives in up to excellent yields via base‐mediated nucleophilic ring‐opening of activated aziridines with 2‐(2‐bromophenyl)‐1 H ‐benzimidazoles, followed by a Cu‐powder‐mediated intramolecular C–N cyclization reaction. Conformational isomerism in the ring‐opening products due to restricted rotation around the N─C bond was observed. These rotameric compounds were characterized through variable‐temperature NMR (VT‐NMR) and further supported by DFT calculations.