The lanthanide-catalyzed oxidative C-O coupling of 1,3-dicarbonyl compounds with diacyl peroxides, specifically the cyclic malonyl peroxides, has been developed. An important feature of this new reaction concerns the advantageous role of the peroxide acting both as oxidant and reagent for C-O coupling. It is shown that lanthanide salts may be used in combination with peroxides for selective oxidative transformations. The vast range of lanthanide salts (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Y) catalyzes oxidative C-O coupling much more efficiently than other used Lewis and Bronsted acids. This oxidative cross-coupling protocol furnishes mono and double C-O coupling products chemo-selectively in high yields with a broad substrate scope. The double C-O coupling products may be hydrolyzed to vicinal tricarbonyl compounds, which are otherwise cumbersome to prepare. Based on the present experimental results, a nucleophilic substitution mechanism is proposed for the C-O coupling process in which the lanthanide metal ion serves as Lewis acid to activate the enol of the 1,3-dicarbonyl substrate. The side reactions-chlorination and hydroxylation of the 1,3-dicarbonyl partners-may be minimized under proper conditions.

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 %).

Malonyl peroxides act both as oxidants and reagents for C−O coupling in reactions with methyl and silyl enol ethers. In the proposed conditions, the oxidative C−O coupling of malonyl peroxides with enol ethers selectively proceeds, bypassing the traditional Rubottom hydroxylation of enol ethers by peroxides. It was observed that the oxidative [5+2] cycloaddition of malonyl peroxides and enol ethers is the key stage of the discovered process. Oxidative C−O coupling of silyl enol ethers leads to the formation of α‐acyloxyketones with a free carboxylic acid group. A specially developed preparative one‐pot procedure transforms ketones via silyl enol ethers formation and the following coupling into α‐acyloxyketones with yields 35–88%. The acid‐catalyzed coupling with methyl enol ethers gives remarkable products while retaining the easily oxidizable enol fragment. Furthermore, these molecules contain a free carboxylic acid group, thus these nontrivial products contain two usually incompatible acid and enol ether groups.