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Updated: Dec 21, 2025

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
Cyclopropenylidenephosphoranes: Rearrangement to Azetidinylidene-Methylphosphoniums
Clève Dionel Mboyi1, Albert Poater2, Jordi Poater3
1LCC-CNRS, Université de Toulouse, CNRS, UPS, 205 Route de Narbonne, Cedex 4 31077 Toulouse, France.
Abstract:
Attempts at preparing cyclopropenylphosphonium salts by P-quaternization of α-aminophosphines with bisdiisopropylaminocyclopropenium tetrafluoroborate led to azetidin-2-ylidene methylphosphoniums as unexpected isomers, in 57-85% yields. The basic structure of the products is discussed on the basis of X-ray crystallography analysis. The unprecedented 3 → 4 ring expansion process is argued to be driven by an ambivalent aromatic vs antiaromatic character (or loss of aromaticity) of the primary phosphonium product. On the basis of DFT calculations, a mechanism involving a concerted 1,4-hydride shift/electrocyclization process as the rate-determining step is proposed and discussed vs possible alternatives.
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