As a kind of versatile synthons, α-oxoketene dithioacetals have found their wide utilizations in organic synthesis. Owing to the interaction between two electron donating groups(RS) and an electron withdrawing group in the α position, the α-carbon atom of α-EWG ketene S,S-acetals shows a high nucleophilicity. In this paper, the reactions of α-acetyl cyclic ketendithioacetals with a series of acyl chlorides were performed and a new route to the C～C bond formation reaction at the α-carbon atom of α-oxoketene dithioacetals was described. By the above reactions, α-acetyl-α-acyl ketendithioacetals were prepared with good to high yields(55%～82%) via the acylation of α-acetyl cyclic ketendithioacetals at the α-carbon atom of α-acetyl ketendithioacetals mediated by titanium tetrachloride in dry dichloromethane at reflux temperature. The mechanism of the acylation between compound 1 and acyl chloride was proposed, which belongs to nucleophilic addition-elimination reaction.
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.
