Interaction of a lithiated nitronyl nitroxide with polyfluorinated 1,4-naphthoquinones

• Published in: Tetrahedron 2018-07, Vol.74 (28), p.3924-3930
• Main Authors: Zhivetyeva, S.I., Zayakin, I.A., Bagryanskaya, I.Yu, Zaytseva, E.V., Bagryanskaya, E.G., Tretyakov, E.V.
• Format: Article
• Language: English
• Subjects: 1,4-Naphthoquinones; ESR spectra; Iminonitroxides; Nitronyl nitroxides; Organic diradicals; X-ray diffraction study
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2018.05.075

A 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl lithium derivative was found to react with 2-methoxypentafluoro-1,4-naphthoquinone to form a product of addition at the carbonyl function: radical 2-(3,5,6,7,8-pentafluoro-1-hydroxy-2-methoxy-4-oxo-1,4-dihydronaphthalen-1-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl. The yield of the addition product increased with temperature and reached 84% at 0 °C. The reaction of the lithium derivative with hexafluoro-1,4-naphthoquinone gave rise to a product of addition at both carbonyl groups, namely, nitronyl nitroxide diradical 2,3,5,6,7,8-hexafluoro-1,4-bis(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazole-2-yl)-1,4-dihydronaphthalene-1,4-diol in a 16% yield. The structures of both mono- and diradical were solved by X-ray diffraction analysis, which revealed formation of an intramolecular H-bond between the OH group and nitroxide oxygen. According to electron paramagnetic resonance (EPR) spectroscopy, the obtained mono- and dinitroxide are prone to spontaneous deoxygenation in a toluene solution to give corresponding iminonitroxides. In water, they are much more stable. [Display omitted]