A N-heterocyclic carbene derived highly regioselective ambident C-C-S and C-C-N 1,3-dipolar system.

N-Heterocyclic carbene derived 2-phenylthiocarbamoyl benzimidazolium and imidazolinium inner salts are a unique ambident C-C-S and C-C-N 1,3-dipolar system able to undergo highly efficient and regioselective cycloaddition with dimethyl acetylenedicarboxylate and ethyl propiolate to furnish, respectively, spiro[imidazole-2,3'-thiophene] and spiro[imidazole-2,3'-pyrrole] derivatives in good to excellent yields.