Dialkyl dicyanofumarates as oxidizing reagents for the conversion of thiols into disulfides and selenols into diselenides

Aliphatic and aromatic thiols react smoothly with dialkyl dicyanofumarates in CH2Cl2 at room temperature to give the corresponding disulfides in excellent yields. Aliphatic 1,2-, 1,3-, and 1,4-dithiols afford cyclic disulfides. Analogous reaction courses were observed starting with selenols, and the required diselenides were also formed in nearly quantitative yields. In all of the reactions, dialkyl dicyanosuccinates formed as a 1:1-mixture of diastereoisomers as the only other product. Cysteamine (2-mercaptoethylamine) behaved differently; the Michael addition of the primary amine group led to complete consumption of the dicyanofumarate, and the formation of the disulfide containing the enamine moiety occurred without the formation of dicyanosuccinate