Homogeneously catalyzed epoxidation of α,β-unsaturated ketones using simple aluminum salts and aqueous H2O2—Is it possible?

Simple aluminum salts activate hydrogen peroxide towards α,β-unsaturated ketones, affording as major products α,β-epoxyketones. The pathway of this reaction involves the interaction between [Al(H2O)6]3+ and H2O2, through hydrogen bonds, in the second-coordination sphere. This interaction enhances the proton exchange between non-coordinated water and hydrogen peroxide, as detected by 1H NMR experiments. By this means, the hydroperoxide anion, formed as reactive intermediate in the proton exchange between H2O and H2O2, can be trapped by α,β-unsaturated ketones. Surprisingly, this pathway is not followed when diethylmaleate is used as substrate. In this case, the radical addition of THF to the CC bond of diethylmaleate takes place with high selectivity, affording 2-(THF)-derivatives with high yields.

Simple aluminum salts can induce nucleophilicity to H2O2 allowing epoxidation at electron-deficient CC bonds. Although the ionic pathway involving HOO− species is prevailing towards α,β-unsaturated ketones, the radical pathway is revealed as the exclusive route followed in the reaction with diethylmaleate. In this reaction, radical addition of THF to diethylmaleate takes places selectively, affording 2-(THF)-derivatives with high yield.Figure optionsDownload as PowerPoint slide