Radicals from Oxygenated Pyrans

Parkanyi and R. Zahradnik, Collect. Czech. Chem. Commun. 27, 1355 (1962). 

The polarography of anthocyanidins was studied several years ago by Zuman. A more recent investigation of pelargonidin (62), cyanidin, and various model flavylium ions has been published by Harper and 

Oxidation of hydroxybenzopyrones leads to the formation of radicals which have been studied by Thus, Ashworth found 

Sharma and Seshadri of the oxidative dimerization of both esculetin and isoscopoletin (7-methylesculetin) upon treatment with [Fe(DMF)3Cl2] [FeC ] strongly suggests the participation of 65 and its 7-methylated analog, or their protonated forms. The coupling positions are consistent with the positions of high spin population indicated in 65. 

The electronic absorption spectrum of 69 has been obtained by Shida et al ° and accounted for in MO terms. ESR spectra have also been measured and assigned for nitrated derivatives of 69.  

4-one failed to give a ketyl on electrochemical reduction in various organic 

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Phenols (e.g., phenol itself [CeHs-OH or Ar-OH], Table 6.10, item 2) and their esters (e.g., the trifluoroacetate ester of phenol [C6H5-O2CCF3 or Ar02CCH3], Table 6.10, item 3) have been oxidized with air and oxygen (O2), in neutral and alkaUne solutions, with and without ionic and/or radical catalysts and/or irradiation and in a variety of solvents. Enzymes (this chapter and Chapter 12) from a wide variety of sources have also been used. Frequently, oxidation of aromatic systems to phenols cannot be stopped before quinones and products of ring fragmentation occur and numerous, sometimes ill-defined, products result. Thus, as shown in Equation 6.80, oxidation of the polynuclear hydrocarbon chrysene with anunonium cerium(IV) sulfate [ceric ammonium sulfate, Ce(NH,)4(S04)4] is reported to produce 6H-benzo[d]naphtho[l,2-/>]pyran-6-one (8% yield) and a quinone (23% yield). The remainder of the product(s) (69%) was unidentified. 

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