New synthesis of 2-amino-3-cyano-4,5-tetramethylenethiophene

We have shown that 2-amino-3-cyano-4,5-tetramethylenethiophene (IV) is formed in the reaction of cyclohexanethione (I) with malononitrile (II) and sulfur in the presence of triethylamine. The reaction proceeds through a step involving the formation of cyclohexylidenemalononitrile (III) and occurs via attack by the malononitrile anion on the sulfur atom of the thiocarbonyl group of I. Δ^2,α-Bornanylmalononitrile (V) was similarly obtained from thiocamphor and II; the latter reaction cannot be realized with camphor because of the steric hindrance of the carbonyl carbon atom.