The carboxyl derivatives of 6,8-di-(tert.-butyl)phenoxazine: Synthesis, oxidation reactions and fluorescence

• Published in: Tetrahedron 2019-01, Vol.75 (4), p.538-544
• Main Authors: Ivakhnenko, Eugeny P., Knyazev, Pavel A., Romanenko, Galina V., Kovalenko, Anastasiia А., Ivakhnenko, Tatyana E., Revinskii, Yurii V., Minkin, Vladimir I.
• Format: Article
• Language: English
• Subjects: Arylaminophenols; Fluorescence; Phenoxazine; Phenoxazine-carboxylic acids
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2018.12.047

New carboxyl-containing o-aminophenols and phenoxazines were synthesized by condensation of 3,5-di-(tert.-butyl)-quinone with p-aminobenzoic and anthranilic acids. Oxidative transformations of the o-aminophenols and intermediate o-iminoquinones occur with the formation of the ESR detected phenoxazinyl radicals, which furthermore transform to phenoxazines or the dimeric products emerged through the radical attack at the C1 carbon of a formed phenoxazine. Molecular structure of the dimer obtained by oxidation of methyl ester of 4-[3,5-di-(tert.-butyl)-1-(2′-hydroxyphenyl)amino]benzoic acid was X-ray determined. Reaction of 4-[3,5-di-(tert.-butyl)-1-(2′-hydroxyphenyl)amino]benzoic acid with thionyl chloride gives rise to the formation of a derivative of 2-oxido-3H-benzo[d,j][1,2,3]oxathiazol system, the structure of which was established using X-ray crystallography. Solutions of methyl-6,8-di-(tert.-butyl)-10H-phenoxazine-3-carboxylate solvents display intense fluorescence covering a broad spectral region in the range of 400–600 nm. [Display omitted] •New carboxyl-containing o-aminophenols and phenoxazines were synthesized.•Oxidation of the phenoxazines occurs with the formation of the ESR detected radicals.•Radical dimerization of phenoxazine leads to highly fluorescent product.•Phenoxazine-1 carboxylic acid exists as the inner salt in polar solvents.