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Updated: Dec 28, 2025

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
Intramolecular (4 + 2) cycloaddition of aryl-1-aza-2-azoniaallene salts: A practical approach to highly
Ram C Dhakal1, Matthias Brewer1
1Department of Chemistry, The University of Vermont, 82 University Place, Burlington, VT 05405, United States.
Abstract:
We report an improved two-step reaction sequence that gives tricyclic protonated azomethine imine products containing a 1,2,3,4-tetrahydrocinnoline scaffold in high yield. This sequence involves the oxidation of aryl hydrazones with TFAA-activated DMSO to give the corresponding α-trifluoroacetoxyazo products, which react readily with TMSOTf to give 1-aza-2-azoniaallene salt intermediates that undergo intramolecular (4+2) cycloadditions with pendent alkenes. This reaction sequence is more general, more practical and more environmentally friendly than our initially reported method. The cycloaddition provides exceptionally sterically-hindered products in high yield.
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