Unprecedented reaction course of 1-phenyl-2H,6H-imidazo[1,5-c]quinazoline-3,5-dione with 3-M excess of ethylene oxide

The reaction of 1-phenyl-2H,6H-imidazo[1,5-c]quinazolino-3,5-dione (4) with 3-molar excess ethylene oxide was described. The resulting product was characterized by spectroscopic techniques (1H-, 13C-NMR, IR, and UV) and by X-ray crystallography. It was expected to produce a product of the subsequent reaction in the hydroxyl groups of the initially formed diol—1-phenyl-2,6-bis(2-hydroxyethyl)imidazo[1,5-c]quinazoline-3,5-dione (7) with ethylene oxide (5). However, crystallographic studies revealed that the proper and only product of the reaction is 3-{2-[1,3-bis(2-hydroxyethyl)-2-oxo-4-phenylimidazolidin-5-yl]phenyl}-1,3-oxazolidin-2-one (8). This product was formed by quinazoline ring opening which occurred in the presence of more than 2-molar excess ethylene oxide. In the work, the exemplary reaction mechanism explaining the formation of the unexpected product was proposed. In order to understand the reasons of quinazoline ring opening, the quantum mechanical modeling was performed. Energy of transition states indicated that the reaction with the third mole of ethylene oxide was controlled by kinetics.