Rearrangements of N-Heterocyclic Carbenes of Pyrazole to 4-Aminoquinolines and Benzoquinolines

1-Phenyl-substituted pyrazolium salts, formed by quaternization of pyrazoles with benzyl halides or long-chain alkyl halides, deprotonate to pyrazol-3-ylidenes that undergo a sequence of ring-opening, ring-closure, and tautomerization to new substituted 4-aminoquinolines Similarly, 1-naphthyl-substituted pyrazolium-3-carboxylates decarboxylate on heating in toluene to give benzoquinolines in excellent yields by an analogous reaction pathway DFT calculations indicate that the ring transformation proceeds through a sequence of intramolecular elimination, imine inversion and 6 pi-electrocyclization steps.