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Updated: Jun 5, 2026

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
Trapped Cycloadducts of 1-Azabutadienes via Microwave-Assisted Ring Opening of N-Acyl-2-azetines
Chuyi Su1, Jacob P Cameron1, Paul V Bernhardt1
1School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia.
Abstract:
Disclosed herein is the observation that electrocyclic ring opening of select N-acyl-2-azetines can occur under microwave irradiation or conventional heating to give the corresponding 1-azabutadiene systems, under more mild and accessible conditions than the previously reported flash vacuum pyrolysis conditions. The intermediate 1-azabutadienes, successfully detected by NMR analysis in the case of the 2-naphthoyl system, subsequently undergo intermolecular Diels-Alder reactions with the parent azetine systems to form heterobicyclic dimers, as confirmed by X-ray crystallography. Alternatively, if the 1-azabutadiene is generated in the presence of an electron-rich dienophile (e.g., enol ether or enamine), dimer formation is partially or fully suppressed, giving the corresponding cycloadducts instead. These observations are in agreement with the included theoretical calculations.
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