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Terrier, F ; Beaufour, M ; Halle, JC ; Cherton, JC ; Buncel, E

A remarkably facile oxygen transfer in a nitrobenzofuroxan structure activated through sigma-complex formation

Tetrahedron Letters 42 (27) 4 499-4501

par Administrateur - publié le

Abstract :

Treatment of 4,6-dinitrobetlzofuroxan (DNBF) with the imidazoline 1-NRf is found to afford a zwitterionic nitrogen-bonded complex (2-NRf) which, in the presence of base (Et3N), undergoes a slow but quantitative transformation to give 7-hydroxy-4,6-dinitrobmzofurazan (5) as the final product. Overall, an oxygen transfer has thus occurred from the N-oxide function to the carbocyclic moiety of DNBF. The key point in this transformation is shown to be a facile abstraction of the sp(3) hydrogen bonded at C-7 of 2-NRf, providing important new evidence that the parent DNBF structure is extremely electron-withdrawing (’super-electrophile’). The overall conversion is also an unusual case of a catalytic process in which the catalysts (both 1-NRf and Et3N) partake to form covalent reaction intermediates and thereby lower the activation energy, resulting in a facile reaction. (C) 2001 Elsevier Science Ltd. All rights reserved.