Abstract
N/C-Hydroxylated spirofused derivatives of 2,5-dihydroimidazole which were synthesized by condensation of 4-(4-hydroxyphenyl)cyclohexanone with aryl hydroxylaminoalkyl ketones in the presence of ammonia were determined to be trans-ee-isomers of 1,4-cyclohexane framework by NMR spectroscopy. Oxidation of the cyclic hydroxylamino moiety followed by acylation of the phenolic hydroxyl group with 4-alkyloxybenzoic acid chlorides led to the corresponding spirocyclic nitroxides bearing two mesogenic fragments.
Highlights
The rapid development of synthetic chemistry of stable nitroxyl radicals has led to significant advances in the field of their practical importance
In this work we describe an approach to the synthesis of stable spirocyclic nitroxides 2-4 with a 2,5-dihydroimidazole structure (Figure 1)
We have developed a convenient approach to the synthesis of stable nitroxides of 2,5dihydroimidazole series bearing two identical and two different mesogenic groups located in both sides of spirofused heterocyclic and cyclohexane frameworks
Summary
The rapid development of synthetic chemistry of stable nitroxyl radicals (aminoxyls) has led to significant advances in the field of their practical importance. Condensation of commercially available 4-(4-hydroxyphenyl)cyclohexanone (7) with 2-hydroxylamino ketones 5 and 6 in methanol saturated with ammonia at ambient temperature gave imidazolines 8 and 9 with 70% and 97% yield, respectively. For the synthesis of nitroxide 4 with two different mesogenic acyl groups (n ≠ m), radical 11 was initially treated with one equiv of tert-BuOK and one equiv of 4-octyloxybenzoic acid chloride (12a) was added to the reaction mixture to give monoacyl derivative 13 in 28% yield after the starting radical 11 were separated chromatographically. Reaction of nitroxide 13 with 4-nonyloxybenzoic acid chloride (12b) afforded the target radical 4 possessing two different mesogenic acyl groups in 21% yield.
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