Ambivalent Nucleophilicity of 1,4,5-Trisubstituted Imidazole-2-thiones in Reactions with Dimethyl Acetylenedicarboxylate and Phenylisocyanate

The 1,4,5-trisubstitued 2,3-dihydro-1H-imidazole-2-thiones 1 react with electrophilic reagents via the S- or the N(3)-atom. The reaction with dimethyl acetylenedicarboxylate in methanol at room temperature occurs by the nucleophilic addition of the S-atom to give the corresponding 2-[(1H-imidazol-2-yl)sulfanyl]fumarates 4 in high yield. On the other hand, imidazole-2-thiones 1 react with phenylisocyanate in dichloromethane at room temperature to yield 2,3-dihydro-2-thioxo-1H-imidazole-1-carboxamides 5. The structures of both types of adducts were established by X-ray crystallography.