Double Michael addition of dithiols to acetylenic carbonyl compounds under the influence of molecular sieve and dimethyl sulfoxide

Double Michael addition of dithiols such as 1,3-propanedithiol and 1,2-ethanedithiol to α,β-acetylenic carbonyl compounds in the presence of molecular sieve and dimethyl sulfoxide proceeds very smoothly to afford the corresponding β-keto 1,3-dithianes and β-keto 1,3-dithiolanes, respectively, in good to high yields.