Tautomeric 2-arylquinolin-4(1H)-one derivatives- spectroscopic, X-ray and quantum chemical structural studies

A convenient method for the synthesis of 2-aryl-1-methylquinolin-4(1H)-ones is described. Spectroscopic and X-ray crystallographic techniques as well as quantum chemical calculations have been used to probe the structure of potentially tautomeric 2-arylquinolin-4(1H)-ones in solution phase, gas phase and solid state. The exclusive NH-4-oxo nature of the title compounds in solution phase (NMR) and solid state (IR and X-ray) is also corroborated by comparison of their spectroscopic data with those of the corresponding 2-aryl-1-methylquinolin-4(1H)-one and 2-aryl-4-methoxyquinoline derivatives. Results from mass spectrometric analysis confirm the coexistence of the 4-quinolinone and 4-hydroxyquinoline isomers in the gas phase and this is supported by quantum chemical computations. q 2003 Elsevier B.V. All rights reserved