Activation of Elemental Sulfur by Electrogenerated Cyanomethyl Anion: Synthesis of Substituted 2-Aminothiophenes by the Gewald Reaction

The activation of elemental sulfur (S(8)) has been achieved by means of electrogenerated cyanomethyl anion [easily obtained by galvanostatic reduction from acetonitrile/tetraethylammonium hexafluorophosphate (MeCN-Et(4)NPF(6))]. The "activated" sulfur reacted with ylidenernalononitriles to give substituted 2-aminothiophenes in very high yields. This variation of the Gewald reaction has been carried out using only catalytic amounts of electricity and supporting electrolyte. A proposed mechanism for the interaction between S(8) and cyanomethyl anion is described.