Azodicarhoxamides vs. azodicarboxylates in reactions against thioisomuenchnones: 1,3-dipolar cycloaddition or nucleophilic addition?

Article abstract of DOI:10.1002/ejoc.200901349

This communication presents the first study on the use of azodicarboxamides against mesoionic heterocycles as 1,3-dipoles. The reactions yield thioureido compounds. Their formation could be explained, on the basis of experimental results and preliminary theoretical calculations, by a nucleophilic addition followed by rearrangement; however, a formal 1,3-dipolar cycloaddition and subsequent fragmentation and rearrangement of the transient cycloadducts could not be ruled out. Reactions are carried out in refluxing toluene and are complete in 90-240 min. Structural elucidation of the products is based on single-crystal X-ray analysis, as well as other spectroscopic data and 2D-NMR correlations.