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 degrees 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%).