Irradiation of 2, 3, 6-trialkyl-4-pyrimidinones 1 and the thermal reactions of the Dewar 4- pyrimidinones 2 in aliphatic carboxylic acid solutions gave the corresponding tetraalkylppimidinium-5-carboxylates 3. The structures of the betaines 3 were established by spectroscopic and chemical methods. The 13C-labeling experiments indicated that the carboxy carbon atom of the carboxylic acid is incorporated in the 2 position of the ...