Simple Synthesis of 1,3-Dialkylimidazole-2-chalcogenones (E=S, Se, Te) from NHC-CO2 Adducts

We present a high yield synthesis of 1-ethyl-3-methyl-imidazole-2-chalcogenones from readily available imidazolium-2-carboxylate zwitterions NHC-CO2 and elemental chalcogens. In sharp contrast to previous syntheses for corresponding thiones and selones from imidazolium salts and bases our reactions proceed fast with full instead of low conversion and selectivity, decarboxylation is the driving force. Furthermore, this strategy is applicable to all heavier chalcogens including tellurium. Vacuum sublimation of imidazole-2-chalcogenones is implemented as convenient method of purification leading to solid instead of liquid products reported in literature. Newly prepared 1-ethyl-3-methyl-imidazole-2-tellone was characterized by XRD analysis and a correlation study of Te-125 NMR and C-13 NMR shifts with respect to known representatives. The reaction of NHC-CO2 with TMS2S leads to NHC-COS, characterized by XRD analysis, whereas heavier chalcogen derivatives TMS2E (E=Se, Te) did not react with NHC activated CO2.