Azodicarboxamides vs. Azodicarboxylates in Reactions against Thioisomünchnones: 1,3‐Dipolar Cycloaddition or Nucleophilic Addition?

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