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Cyclic nitrones of the imidazole series, containing a sterically hindered phenol group, are promising objects for studying antioxidant activity; on the other hand, they can form persistent hybrid phenoxyl-nitroxyl radicals (HPNs) upon oxidation. Here, a series of 5-aryl-4,4-dimethyl-4 H -imidazole 3-oxides was obtained by condensation of aromatic 2-hydroxylaminoketones with 4-formyl-2,6-dialkylphenols followed by oxidation of the initially formed N -hydroxy derivatives. It was shown that the antioxidant activity of both 1-hydroxy-2,5-dihydroimidazoles and 4 H -imidazole 3-oxides increases with a decrease in steric volume of the alkyl substituent in the phenol group, while the stability of the corresponding HPNs generated from 4 H -imidazole 3-oxides reveals the opposite tendency.

2-(3,5-Di- tert -butyl-4-hydroxyphenyl)-5-(4-iodophenyl)-4,4-dimethyl-4 H -imidazole 3-oxide reacts with phenylboronic acid and its substituted derivatives in a cross-coupling reaction of the Suzuki-Miyaura type to form 5-biphenyl derivatives of 4 H -imidazole- N -oxide. Interaction of the same compound with B 2 (pin) 2 in the presence of PdCl 2 (PPh 3 ) 2 proceeds through the formation of intermediate 1,3,2-dioxoborolane and leads to the product of homocoupling: biphenyl-bis(imidazole). Oxidation of the resultant imidazoles with lead dioxide quantitatively yields stable conjugated phenoxyl-nitroxyl mono- and diradicals, which are of interest as electroactive paramagnetic materials. The crystal structure of the monoradical, 2,6-di- tert -butyl-4-[1-oxido-4-(biphenyl-4-yl)-5,5-dimethyl-1 H -imidazole-2(5 H )-ylidene]cyclohex-2,5-dienone, its magnetic susceptibility, EPR spectra of the obtained hybrid radicals in solution, and cyclic voltammetry characteristics of 4 H -imidazoles were studied., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)