Abstract
AbstractLewis base catalyzed electrophilic aromatic halogenation using N‐halosuccinimides (NsX; X=Cl, Br, I) under mild conditions has attracted much attention, but the detailed mechanism remains elusive. Using the aniline MesNH2 and anisole PhOMe as the typical base catalyst and aromatic substrate, respectively, a novel mechanism is revealed by extensive DFT calculations. The autogenic protonation of imine XMes=NH (via Mes=NH+ mediated dimerization of MesNH2) is crucial to initialize the electrophilic halonium X+ transfer to nucleophilic substrates. It is shown that the aniline MesNH2 and more basic imine XMes=NH may act as efficient halonium X+ and proton H+ shuttles, respectively, connected by the arenium XMesNH2+. Non‐coordinating MesNH3+ salts are suggested as efficient catalyst for electrophilic iodination. Without suitable stabilization of the highly basic anion Ns−, the generally accepted concept of Lewis base catalyst as simple X+ shuttle will never work efficiently due to a high thermodynamic barrier. In general, autogenic or additional acid additives should be used for more efficient Lewis base catalyzed halogenation.
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