Ambident Reactivity of Imidazolium Cations as Evidence of the Dynamic Nature of N‐Heterocyclic Carbene‐Mediated Organocatalysis

This work reveals ambident nucleophilic reactivity of imidazolium cations towards carbonyl compounds at the C2 or C4 carbene centers depending on the steric properties of the substrates and reaction conditions. Such an adaptive behavior indicates the dynamic nature of organocatalysis proceeding via a covalent interaction of imidazolium carbenes with carbonyl substrates and can be explained by generation of the H‐bonded ditopic carbanionic carbenes. Ambident nucleophilic reactivity of imidazolium cations at the C2 or C4 carbene centers reveals the dynamic nature of organocatalysis proceeding via an interaction of imidazolium carbenes with carbonyl substrates. Formation of the H‐bonded abnormal carbene (aNHC) and ditopic carbanionic carbene (dcNHC) was theoretically modeled in order to explain this dynamic behavior.