Remarkably stable mesoionic oxazolones possessing an oxazolo [3, 2-a] quinolinium structure (5a–b), 8, 16, 17) were obtained by the double cyclisation of phenylglycine-o- carboxylic acids (3a–c) in refluxing acetic anhydride or in benzoic anhydride at 140°, The 0- Ac group was eliminated to give the corresponding lactones (6a–b) or replaced by O-Ts (7). IR stretching vibrations of the endo-carbonyl were in the range 1710–1768 cm− 1, while ...