Mechanism for the Oxidative Cleavage of Electron-deficient Acetylenes with Alkaline Hydrogen Peroxide

Abstract

4-Phenyl-3-butyn-2-one (1a) was effectively cleaved by alkaline hydrogen peroxide to afford benzoic and acetic acids. The rate ratio for the addition of HOO⁻ and HO⁻ to 1a resulted in k_HOO⁻/k_HO⁻=1400, which is comparable to that of benzylideneacetone. The major reaction of the cleavage proceeds via benzoylacetone. As a minor pathway, α-keto oxirene intermediate is formed and rearranges only to α-benzoylpropionate in a different way from the corresponding diketo carbene. α-Keto esters are found to be converted by HOO⁻ to α-alkoxy ketones via a novel oxidative substitution of ester group. Methyl phenylpropiolate is oxidized by HOO⁻ similarly as 1a. The mechanism is discussed on the basis of oxirene intermediate inconvertible to keto carbene.