Oxovanadium Complex-Catalyzed Aerobic Oxidation of Propargylic Alcohols

A catalytic system consisting of vanadium oxyacetylacetonate [VO(acac)2] and 3 A molecular sieves (MS3A) in acetonitrile works effectively for the aerobic oxidation of propargylic alcohols [R1CH(OH)C⋮CR2] to the corresponding carbonyl compounds under an atmospheric pressure of molecular oxygen. Although the reactivity of α-acetylenic alkanols (R1 = alkyl) is lower compared to that of the alcohols of R1 = aryl, alkenyl, and alkynyl, the use of VO(hfac)2 as a catalyst and the addition of hexafluoroacetylacetone improve the product yield in these cases. A catalytic cycle involving a vanadium(V) alcoholate species and β-hydrogen elimination from it has been proposed for this oxidation.