MnO2 as Terminal Oxidant in Wacker Oxidation of Homoallyl Alcohols and Terminal Olefins

An efficient and mild reaction conditions for Wacker-type oxidation of terminal olefins of less explored homoallyl alcohols to β-hydroxy-methyl ketones has been developed by using Pd(II) catalyst and MnO2 as co-oxidant. The method involves mild reaction conditions and shows good functional group compatibility along with high regio- and chemoselectivity. While our earlier system of PdCl2/CrO3/HCl produced α,β-unsaturated ketones from homoallyl alcohols, the present method provided orthogonally the β-hydroxy-methyl ketones. No overoxidation or elimination of benzylic and/or β-hydroxy group was observed. The method could be extended to oxidation of simple terminal olefins as well, to methyl ketones displaying its versatility. A application to the regioselective synthesis of gingerol is demonstrated.