Irradiation of the 2, 3, 6-trialkyl-4-pyrimidinones 4 and 18 in liquid ammonia-ether (7: 3) solution at-40 OC gave the corresponding Dewar 4-pyrimidinones, 5 and 19, which decomposed in inert solvents at room temperature and did not revert to the corresponding 4- pyrimidinones, The first-order rate constants for disappearance of 5 and 19 were measured at 10-54" C. The solvolysis reactions of 5 and 19 occur in methanol to give the a-( ...