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Updated: Mar 17, 2026

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
Medium-Ring Nitrogen Heterocycles through Migratory Ring Expansion of Metalated Ureas
Jessica E Hall1, Johnathan V Matlock1, John W Ward1
1School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Abstract:
Simple benzo-fused nitrogen heterocycles (indolines, tetrahydroquinolines, and their homologues) undergo migratory ring expansion through deprotonation of their benzylic urea derivatives with lithium diisopropylamide (LDA) in the presence of N,N'-dimethylpropylideneurea (DMPU). The products of the reactions are benzodiazepines, benzodiazocines, and their homologues, with ring sizes of 8-12. The reactions tolerate a range of substituent patterns and types, and may exhibit enantiospecificity or diastereoselectivity. Considerable complexity is rapidly generated in an efficient synthesis of these otherwise difficult-to-obtain medium-ring nitrogen heterocycles.
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