Selective Oxidation of Vinyl Ethers and Silyl Enol Ethers with Hydrogen Peroxide Catalyzed by Peroxotungstophosphate

The oxidation of vinyl and silyl enol ethers with aqueous hydrogen peroxide was first achieved by the use of peroxotungstophosphate (PCWP) as the catalyst. For example, the oxidation of 1-ethoxy-1-octene with a stoichiometric amount of 35% H(2)O(2) in the presence of PCWP (0.5 mol %) in a mixed solvent of methanol and dichloromethane at room temperature gave 1-ethoxy-1-methoxy-2-hydroxyoctane, a synthetic equivalent of 2-hydroxyoctanal, in 70% yield. The oxidation of acyclic silyl enol ethers such as 1-[(trimethylsilyl)oxy]-1-octene under these conditions gave 1-hydroxy-2-octanone in 72% yield, while the same oxidation in dichloromethane alone resulted in cleavage of the enol double bond to form heptanal in 71% yield. Cyclic silyl enol ethers were converted into the corresponding alpha-hydroxy ketones in 48-71% yields under similar reaction conditions.