Chemistry of free cyclic vicinal tricarbonyl compounds ('1,2,3-triones'). Part 3. Polar and redox reactions of 1,2,3-triones with enamines of different types - News on oxonol dyes, radicals, and biradicals

摘要

The central C=O groups of cyclic 1,2,3-triones possess outstanding electrophilic (electron-pair-accepting) as well as oxidizing (one-electron-accepting) properties. Thus, 1,2,3-triones are chemically related to 1,2- and 1,4-benzoquinones. Whereas polar reactions with carbanion-like (electron rich) species give rise to nucleophilic addition reactions to C=O groups under exclusive C,C-bond formation, SET (single-electron transfer) or redox reactions effect a partial `carbonyl Umpolung' via ketyl intermediates (C,C- and/or C,O-bond formation). Here, we report on numerous reactions between electron-rich, more- or less-polar enamines with 5,5-dimethylcy-clohexane-1,2,3-trione (9a) and 1H-indene-1,2,3-trione (9b). Various new derivatives of basic oxonol dyes were formed, including the first oxonol dye incorporating a 1,3-dioxocyclohexyl moiety. A novel stable radical, 50/50', was obtained from 9b and 11a via addition, hydrolysis, and treatment with cone. H2SO4. Radical 50/50' represents a vinylogous `monodehydroreductone' and is, thus, related to monodehydroascorbic acid (143), to Russell's radical cation (144), to indigo (141/141'), and to quinhydrone.