sabrina bernard

Sydnone imines were deprotonated at C4 to give lithium- stabilized anions which proved to be stable for several months in solution. These anions are elements of the intersection of the substance classes of N-heterocyclic carbenes and mesomeric betaines and can be formulated as anionic N-heterocyclic carbenes. The negative charge translates into high-field shifts of the 13C NMR resonance frequencies of C4 in comparison to other NHCs. Similar to the chemistry of N-heterocyclic carbenes reactions with isocyanates and isothiocyanates gave 4-(N-carbamoyl)-benzoylsydnone imines in trapping reactions. As a result of ring transformations involving the characteristic pi-architecture of the mesoionic framework, however, imidazolidine-2,4-dithiones, imidazolin-2,4-diones and 1,2,4-triazol-5-ones were formed depending on the substitution pattern of the starting materials and the reaction conditions.