Thia- and Selena-Heterocycles Containing Cycloamidine Substructures: Ring Contraction Reactions of 1,3,4-Thia-/Selenadiazines

1,3,4-Thia/selena-diazines proved to be suitable starting materials for ring contraction reactions. Treatment with acetic acid/water mixtures leads to highly substituted 1,3,4-thia/selenadiazoles. In addition, the selenadiazoles formed undergo a fast Dimroth-rearrangement to finally yield derivatives of 1,2,4-triazole. The structures of all new derivatives were confirmed by NMR experiments, mass spectroscopy, elemental analysis and X-ray structural analysis.