Polyoxygen species

Polyoxotungstates, 41 193 Polyoxovanadates, 41 193 Polyoxygen species, 32 115 Polypropylenes, preparation and properties of, 23 299-302... 

The ozonide ion O3 has been clearly characterized by EPR and reflectance spectroscopy. Labeling experiments with 170 indicate that the O3 species contains three inequivalent oxygens forming a bond angle of about 110° and that it decomposes slowly at room temperature to form O ". A second type of species has been reported as O3 but has very different characteristics, since it is stable only at low temperatures and labeling experiments with 170, which indicate two equivalent nuclei, are difficult to interpret the balance of the evidence points toward a more complex polyoxygen species (see Section V,A). The data for O4 indicates that it is likely to exist on the surface under special conditions and we expect to see this confirmed by further studies. 

The oxidative activation of arenes is a powerful and versatile synthetic tactic that enables dearomatization to give useful synthons. Central to this chemistry are hydroxylated arenes or arenols, the phenolic functions of which can be exploited to facilitate the dearomatizing process by two-electron oxidation. Suitably substituted arenols can hence be converted, with the help of oxygen- or carbon-based nucleophiles, into ortho-quinone monoketals and ortho-quinols. These 6-oxocyclohexa-2,4-dienones are ideally functionalized for the construction of many complex and polyoxygenated natural product architectures. Today, the inherent and multiple reactivity of arenol-derived ortho-quinone monoketals and ortho-quinols species is finding numerous and, in many cases, biomimetic applications in modern organic synthesis. 

Aryl triflates have proved to possess approximately the same reactivity as aryl halides in various Pd-catalyzed cross-coupling reactions [100, 101]. In 2009, Alami s group employed aryl triflates for Pd-catalyzed coupling reaction of polyoxygenated aryl A-tosyUiydrazones (Fig. 22) [102]. The catalytic system Pd(OAc)2/Xphos with LiO Bu as base in dioxane was found to be suitable for the reaction. The reaction is initiated by the oxidative addition of aryl triflate to Pd(0) species. Then similar migratory insertion and p-hydride elimination subsequently take place to afford a series of 1,1-diarylethylenes which are of biological interest. 

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