Unusual Method of Making 4-Aminoquinolines

The thermolysis of N-aryl-pyrazoles with a carboxyate substituent leads via decarboxylation to N-heterocyclic carbenes, which rearrange to the aminoquinolines, via a ring-opening ring-closing mechanism (Schmidt A et al, Angew Chem Int Ed, 2010, 49, 2790-2793). N-arylpyrazolium salts also undergo the rearrangement reaction when treated with base, indicating a similar betaine or carbene-like intermediate.