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Keywords:

  • azole anions;
  • kinetics;
  • linear free energy relationships;
  • pyrimidines;
  • regioselectivity

Abstract

The kinetics of the reactions of different heterocyclic anions derived from imidazoles, purines, pyrimidines, and related compounds with benzhydrylium ions and structurally related quinone methides have been studied in DMSO and water. The second-order rate constants (log k2) correlated linearly with the electrophilicity parameters E of the electrophiles according to the correlation log k2 = sN(N+E) (H. Mayr, M. Patz, Angew. Chem.1994, 106, 990–1010; Angew. Chem. Int. Ed. Engl.1994, 33, 938–957) allowing us to determine the nucleophilicity parameters N and sN for these anions. In DMSO, the reactivities of these heterocyclic anions vary by more than six orders of magnitude and are comparable to carbanions, amide and imide anions, or amines. The azole anions are generally four to five orders of magnitude more reactive than their conjugate acids.