The reaction of dimethyl sulfoxide–trifluoroacetic anhydride complex with anilines, phenols, and thiophenols was studied, and the following results were obtained. (1) The yields of a methylthiomethylated product were improved with anilines. The reaction proceeded without significant amount of tar, the unreacted anilines being easily recovered. (2) Selective ortho-methylthiomethylation took place with