Oxidation of Allenes and Alkynes with Hydrogen Peroxide Catalyzed by Cetylpyridinium Peroxotungstophosphate (PCWP)

The oxidation of allenes and alkynes with hydrogen peroxide catalyzed by peroxotungstophosphate (PCWP) was examined. A variety of allenes were first converted into the corresponding α-ethoxy ketones upon treatment with 35% H 2 O 2 under the influence of PCWP in a mixed solvent consisting of ethanol and dichloromethane. When the reaction was carried out using tert-butyl alcohol as a solvent, approximately a 1:1 regioisomeric mixture of α-hydroxy ketones was obtained along with a small amount of a-tert-butoxy ketone. Oxidation of internal alkynes such as 4-octyne by the PCWP-H 2 O 2 system under phase-transfer conditions using chloroform produced α,β-epoxy ketones in good yields. The same reaction in a mixed solvent of ethanol and chloroform produced α,β-unsaturated ketones rather than α,β-epoxy ketones. Plausible reaction paths are proposed for the oxidation of allenes and alkynes by the PCWP-H 2 O 2 system