Selective Oxidative Coupling of 3H‐Pyrazol‐3‐ones, Isoxazol‐5(2H)‐ones, Pyrazolidine‐3,5‐diones, and Barbituric Acids with Malonyl Peroxides: An Effective C‐O Functionalization

Oxidative functionalization of 3H-pyrazol-3-ones, isoxazol-5(2H)-ones, pyrazolidine-3,5-diones, and barbituric acids by malonyl peroxides results exclusively in C−O coupling products. Traditional hydroxylation, formation of carbonyl groups, or oxidative destruction of the heterocyclic ring are not observed. Under optimized reactions conditions – fluorinated alcohols as activating medium and at room temperature (20 – 25 °C) – the selective C−O coupling proceeds in high yields (up to 94 %). The oxidative insertion into the enolizable C−H bond of the substrate is mechanistically viewed as a nucleophilic attack by the heterocycle onto the electrophilically activated malonyl peroxides. For heterocyclic substrates with an active methylene group - 3H-pyrazol-3-ones, isoxazol-5(2H)-ones, and barbituric acids - both C−H bonds are oxidized to afford double oxidative C−O coupling products in good yields (up to 72 %).