The bis(ホシ-hydroxo)-bridged dioxovanadium site in [ホウ-1,2-H2SiV2W10O40]4- catalyzes the epoxidn. of alkenes in the presence of only one equiv. of H2O2 with a high yield of epoxide, high efficiency of H2O2 utilization, unusual regioselectivity, and unprecedented diastereoselectivity. [on SciFinder(R)]