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Keywords:

  • acylazolium ions;
  • kinetics;
  • N-heterocyclic carbenes;
  • nucleophilicity;
  • zwitterions
Thumbnail image of graphical abstract

Oxygen versus carbon: Azolium enolates were generated by the reactions of N-heterocyclic carbenes (NHCs) with methyl phenyl ketene and characterized by X-ray crystallography. Kinetic studies show that the enolate oxygen is 20 times more nucleophilic than the carbon atom, but under thermodynamic control exclusive C-addition products were formed.