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.
