The Unexpected Role of Se^VISpecies in Epoxidations with Benzeneseleninic Acid and Hydrogen Peroxide

Abstract

Benzeneperoxyseleninic acid has been proposed as the key intermediate in the widely used epoxidation of alkenes with benzeneseleninic acid and hydrogen peroxide. However, it reacts sluggishly with cyclooctene and instead rapidly decomposes in solution to a mixed selenonium–selenonate salt that was identified by X‐ray absorption and 77Se NMR spectroscopy, as well as by single crystal X‐ray diffraction. This process includes a selenoxide elimination of the peroxyseleninic acid with liberation of oxygen and additional redox steps. The salt is relatively stable in the solid state, but generates the corresponding selenonic acid in the presence of hydrogen peroxide. The selenonic acid is inert towards cyclooctene on its own; however, rapid epoxidation occurs when hydrogen peroxide is added. This shows that the selenonic acid must first be activated through further oxidation, presumably to the heretofore unknown benzeneperoxyselenonic acid. The latter is the principal oxidant in this epoxidation.

Selenium-Catalyzed Reduction of Hydroperoxides in Chemistry and Biology

“…If we consider a selenol (RSeH, R1 = H, Scheme 1B), subsequent oxidations occur leading to selenenic, seleninic and perseleninic acid/selenonic acid, respectively (Scheme 1B). Recently, Back and coworkers have reported evidence of formation of benzene peroxyselenonic acid in the epoxidation of cyclooctene promoted by selenonic acid/H2O2 [11].…”