A novel synthesis of 2,4-thiophenediamines and their behavior as stable reactive enamines

Reaction of α-chlorothioacetanilides (1) in refluxing methanol provides a new route to stable, reactive 2,4-thiophenediamines (2). These materials display interesting chemical and physical properties, based in large part on the interaction of the anilino groups with nuclear substituents alpha to the thiophene sulfur. Thus 2 is easily protonated, with rapid exchange of the 5-proton, while α-carbon-nitrogen cleavage has been observed for the first time during Raney nickel degradation. The susceptibility of the thiophenediamines to electrophilic attack is further demonstrated by facile formation of 3,5-diamino-2-thiophene carboxanilides (3) and 3,5-diamino-2-thienylphenyl ketones (4) from respective reaction of isocyanates, isothiocyanates, and acid chlorides with 2. Certain interesting and unusual spectral characteristics of these compounds, resembling enamines and enaminoketones, are presented and discussed.