Radicals Containing a Furan Ring and Isoelectronic Species

Cation-Radicals Containing a Furan Ring and Isoelectronic Species 

The 7c-excessive character of furan facilitates single-electron oxidation however, the cation-radicals produced from simple furans are not, in general, persistent. The mediation of 2,5-dimetliylfuran cation-radical (1) has been proposed in anodic oxidations yielding methoxylated, cyanomethoxylated, and acyloxylated products.Although not specifically implicated, cation-radicals may be involved in very similar oxidative reactions.  

Deprotonation of 1 to give the neutral radical 2 under the conditions of anodic cyanomethoxylation has been proposed to account for the occurrence of minor products similar deprotonation has been suggested in a reaction where 2,5-dimethylfuran acts as a highly efficient scavenger for benzoyloxy radicals yielding 2-benzoyloxymethyl-5-methylfuran. The ESR spectra of 2 and its 2-methyl analog have been recorded for the radicals generated 

Cation-radicals from 2-arylfurans have been suggested to be involved in the oxidation of these compounds by ruthenium tetroxide. The suggestion is based on the observation of the capture by the heterocycle of the chlorine from chlorinated solvents and of a broad ESR signal which persists for several days. 

Isobenzofurans were studied for their ECL properties in the early development of the technique. More recently, 1,3-diphenylisobenzofuran cation-radical (3) has been shown to react with superoxide anion Oj to give initially singlet oxygen and 1,3-diphenylisobenzofuran which then undergo cycloaddition and yield ultimately 1,2-dibenzoylbenzene.  

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