Stable and reactive diacetyliminoxyl radical in oxidative C–O coupling with β-dicarbonyl compounds and their complexes

Abstract

As a rule, reactive free radicals used in organic synthesis are too labile to be isolated, whereas persistant radicals are inert and find limited synthetic application. In the present study,...

Two Discoveries in One Crystal: σ-Type Oxime Radical as an Unforeseen Building Block in Molecular Magnetics and Its Spatial Structure

“…It should be noted that the solution of 3 in CH 2 Cl 2 had a dark red color (similar to the color of the solution of diacetyliminoxyl 2 ), and after the addition of pyrazolone 4 , the color changed to dark green. This result indicates that complex 3 is a convenient precursor of diacetyliminoxyl 2 for long-term storage and thus can be used in oxidative C–O coupling reactions. ,, …”

“…This result indicates that complex 3 is a convenient precursor of diacetyliminoxyl 2 for long-term storage and thus can be used in oxidative C−O coupling reactions. 33,39,43 ■ CONCLUSIONS In summary, for the first time, we succeeded to synthesize and fully characterize the complex of copper(II) with diacetyliminoxyl radical (3). The formation of a stable complex containing both diacetyliminoxyl and acetylacetonate ligands is unprecedented.…”

“…In most studies, iminoxyl radicals were investigated by IR, , UV–vis, electron paramagnetic resonance (EPR), ,,, and NMR spectroscopies, along with quantum chemical calculations ,− and cyclic voltammetry, but the structure of free oxime radicals was not determined directly by X-ray diffraction analysis. To date, only three representatives of stable iminoxyl radicals have been reported, and several works have been devoted to the study of their individual forms. ,− ,− Di- tert -butyliminoxyl, the first synthesized long-lived iminoxyl radical, was extensively studied by Mendenhall and Ingold. ,,− However, at room temperature, this radical is a sky-blue liquid, which makes it unsuitable for study by diffraction methods. Later, in 1974, the first crystalline stable iminoxyl, namely, di-(1-adamantyl)-iminoxyl, was synthesized. , Unfortunately, despite its crystalline state, its molecular and crystal structures were not solved .…”

“…Although iminoxyl radicals have been known since 1964, their application in organic synthesis and materials science was limited until the last decade, when various selective reactions mediated by oxime radicals were developed . In most studies, iminoxyl radicals were investigated by IR, , UV–vis, electron paramagnetic resonance (EPR), ,,, and NMR spectroscopies, along with quantum chemical calculations ,− and cyclic voltammetry, but the structure of free oxime radicals was not determined directly by X-ray diffraction analysis. To date, only three representatives of stable iminoxyl radicals have been reported, and several works have been devoted to the study of their individual forms. ,− ,− Di- tert -butyliminoxyl, the first synthesized long-lived iminoxyl radical, was extensively studied by Mendenhall and Ingold. ,,− However, at room temperature, this radical is a sky-blue liquid, which makes it unsuitable for study by diffraction methods.…”

Diacetyliminoxyl as a selective radical reagent for organic synthesis: dehydrogenation and dehydrogenative C–O coupling reactions

“…The introduction of EWGs to oximes reduces the NO-H BDE 54 and increases the stability of the oxime radical. 43,48,[55][56][57] A number of long-lived oxime radicals derived from 2-(hydroxyamino)-1,3-dicarbonyl compounds showed prolonged life-times up to several hours. 55,56 Among them, diacetyliminoxyl shows the highest stability which is sufficient for its separation from oxidants and for its use as a reagent.…”