No abstract

Thermal decarboxylation of 1‐phenylpyrazolium‐3‐carboxylates from the mesomeric betaine class of substances leads to pyrazole‐N‐heterocyclic carbenes, which immediately rearrange to multiply substituted 4‐aminoquinolines (see scheme). These species are of interest for the synthesis of heterocycles and pharmacologically active compounds.

No abstract

Abstract1‐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 6π‐electrocyclization steps.

Thermische Decarboxylierungen von 1‐Phenylpyrazolium‐3‐carboxylaten aus der Substanzklasse der mesomeren Betaine führen zu den N‐heterocylischen Carbenen des Pyrazols, die sogleich zu vielfältig substituierten und für die Heterocyclen‐ und Wirkstoffsynthese interessanten 4‐Aminochinolinen umlagern (siehe Schema).