Hydroxyflavones, except those containing a 7hydroxy-group, undergo base-catalysed oxygenolysis under mild conditions leading to oxidative cleavage of the heterocyclic ring to give the corresponding depsides and carbon monoxide in excellent yields. The same result is obtained in the reaction of quercetinase, a dioxygenase. The oxygenation of 3,4',7-trihydroxyflavone in aqueous solution gave p-hydroxyphenylglyoxylic acid and 2,4-dihydroxybenzoic acid ; in absolute methanol containing sodium methoxide methyl 4-hydroxyphenylglyoxylate and methyl 2,4-dihydroxybenzoate as well as 4-hydroxyphenylglyoxylic acid were obtained. The formation of these products is rationalized by assuming that 2-hydroperoxy-4',7-dihydroxyflavan-3,4-dione is formed first and is reduced with the intervention of the 7hydroxy-group to give 2,4',7-trihydroxyflavan-3,4-dione, which is solvated and oxidized under the reaction conditions. 2'-Substituted-3-hydroxyflavones were not susceptible to oxygenolysis.

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Cobalt Schiff base complexes [Co(SB)] catalyze the oxidation of anilines (1) with tert-butyl hydroperoxide to give nitrobenzenes 2 and 4-(tert-butylperoxy)-2,5-cyclohexadien-1-imine derivatives 3 in yield distributions depending on the substitution mode of the substrate. 4-Alkyl- and 4-aryl-2,6-di-tert-butylanilines gave mixtures of 2 and 3, where the higher the bulkiness of the 4-substituent, the higher the yield of 2. With 2,4,6-trimethylaniline, the ratio of oxidations of the nitrogen and C-4 atoms was almost the same; but a hydrolyzed product 5 of the imine was obtained. 2,4,6-Triphenylaniline gave only 2. Nitrobenzene derivatives were also obtained from 2,6-dialkylanilines and 4-substituted anilines. The catalytic activity of Co(SB) depended on the nature of the SB ligand:  the formal potential E° and steric factors seem to affect the reaction rate. Kinetic studies showed that the key step may involve hydrogen abstraction from the aniline, presumably by t-BuO• generated from homolytic decomposition of initially formed CoIII(SB)(OO-t-Bu). A precursor of 2 was found to be the nitrosobenzene derivative.

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