Nucleophilic Reactivities of Deoxy Breslow Intermediates: How Does Aromaticity Affect the Catalytic Activities of N‐Heterocyclic Carbenes?

Aromatic or nonaromatic? Kinetic investigations show that structurally analogous saturated and unsaturated N-heterocyclic carbenes have almost identical nucleophilic reactivities, while the corresponding deoxy Breslow intermediates differ dramatically.