Scheme 27 Manganese(III)-catalyzed direct hydroperoxidation of heterocyclic 1,3-di-carbonyl compounds oxylated pyrazolidine-3,5-diones in quantitative yields (Scheme 27) [162]. The structural assignment of the 4-hydroperoxypyrazolidine-3,5-diones was based on the H NMR, C NMR, and IR spectra, elemental analyses, and finally X-ray crystallography.

To examine the applicability of the manganese(III) acetate-catalyzed a-hydroperoxidation of other biologically important heterocyclic 1,3-di-carbonyl compounds, the reaction of the 5-monosubstituted barbituric acids and 3-butyl-4-hydroxy-2-quinolinone was carried out under similar aerobic conditions. Very similar autoxidation results were obtained, giving the corresponding hydroperoxides in excellent or moderate yields (Scheme 27).

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