C?O coupling of Malonyl Peroxides with Enol Ethers via [5+2] Cycloaddition: Non-Rubottom Oxidation

Article abstract of DOI:10.1002/adsc.201900271

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. (Figure presented.).