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Rearrangements of N‐Heterocyclic Carbenes of Pyrazole to 4‐Aminoquinolines and Benzoquinolines
Author(s) -
Dreger Andrij,
Cisneros Camuña Rafael,
Münster Niels,
Rokob Tibor András,
Pápai Imre,
Schmidt Andreas
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201000507
Subject(s) - chemistry , tautomer , pyrazole , ring (chemistry) , intramolecular force , alkyl , medicinal chemistry , aminoquinolines , halide , toluene , imine , stereochemistry , combinatorial chemistry , organic chemistry , catalysis
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 6π‐electrocyclization steps.