The α-acetyl ketene dithioacetals 2, which bear various alkylthio groups, are a kind of important intermediates in organic synthesis. In this paper, dithioacetals 2 were prepared in very high yields (90%—100%) via the deacetylation reaction of the corresponding α,α-diacetyl ketene dithioacetals 1 in the presence of concentrated sulfuric acid. This reaction involves an %in-situ% electrophilic addition-deacetylation mechanism and shows the nucleophilicity of the α-carbon atom in α-oxo ketenedithioacetals. Meanwhile, when the reaction time was prolonged to 22—25 h, the β-keto thiolesters 3a and 3c were produced in good yields.
