Imidazole derivatives. Part 31. On the reaction of 2,3-dihydroimidazol-2-ylidenes with pentafluoropyridine. Carbenes as reactants in nucleophilic aromatic substitution.
1,3,4,5-Tetramethyl- and 1,3-diisopropyl-4,5-dimethyl-2,3-dihydroimidazol-2-ylidene react immediately with pentafluoropyridine to form the corresponding 2-(tetrafluoropyridyl)imidazolium salts I (R = Me, CHMe2) in good yields. In contrast with I (R = Me), alkyl fluoride is eliminated from I (R = CHMe2) to give 1-isopropyl-4,5-dimethyl-2-(tetrafluoropyrid-4-yl)imidazole, which gives a H-bridged dimer (II) in the solid state. The x-ray structures of 1,3-diisopropyl-4,5-dimethyl-2-(tetrafluoropyridyl)imidazolium chloride and II are reported.
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