3-dithianes using 30% hydrogen peroxide catalyzed by iron(III) acetylacetonate–sodium iodide. The use of niobium(V) chloride as a catalyst instead of iron(III) acetylacetonate was also effective, except in synthesizing some acyltrimethylsilanes. Acylsilanes were obtained efficiently from dedithioacetalization of 2-silylated 1,3-dithianes using 30% hydrogen peroxide catalyzed by iron(III) acetylacetonate–sodium