p‐TSA‐Mediated Four‐Component Reaction: One‐Step Access to Mesoionic 1H‐Imidazol‐3‐ium‐4‐olates, Direct NHC Precursors

Abstract p ‐TSA‐mediated four‐component condensation is described. The reaction of an isocyanide, amine, aldehyde, and amide catalyzed by p ‐TSA afforded diversely substituted mesoionic 1 H ‐imidazol‐3‐ium‐4‐olates in one step. These products were obtained in good to excellent HPLC purity under mild reaction conditions. This formation of mesoionic compounds, structurally related to sydnones and münchnones, represent attractive intermediates and direct precursors for anionic N‐heterocyclic carbenes. Atom economy, time efficiency, and commercially available starting materials make this one‐pot synthesis user‐friendly. magnified image