Nucleophilic Substitution of 4H-Imidazolesby Thioles: New Starting Materials for Tetraazafulvalenes and Fused Heterocycles

Summary.  Different reactivities towards the 4H-imidazoles 1 depending on the nature of the sulfur containing nucleophile were observed. Whereas H₂S and aromatic thioles led to 4,5-diaminoimidazoles in the course of a reduction process, treatment with aliphatic mercaptanes resulted in a substitution-reduction-dimerization cascade which finally gave bis-imidazoles. Their oxidative modification in presence of m-chloroperbenzoic acid then allowed new 1,3,5,7-tetraazafulvalenes to be easily obtained. Treatment of the bis-imidazoles with acetylene dimethyldicarboxylate caused cleavage of the central bond, thus leading to the formation of derivatives which are of interest for the transformation into fused heterocycles such as imidazo[4,5-b]azepines. Received May 22, 2000. Accepted June 19, 2000