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

Abstract Treatment of 4,6-dinitrobenzofuroxan (DNBF) with the imidazoline 1-NR f is found to afford a zwitterionic nitrogen-bonded complex ( 2-NR f ± ) which, in the presence of base (Et 3 N), undergoes a slow but quantitative transformation to give 7-hydroxy-4,6-dinitrobenzofurazan ( 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-NR f ± , 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-NR f and Et 3 N) partake to form covalent reaction intermediates and thereby lower the activation energy, resulting in a facile reaction.