HYDROGEN-DEUTERIUM EXCHANGE OF THIAPYRONES N-METHYLPYRIDONES AND N-METHYLPYRIMIDONES IN BASIC MEDIA

Base-catalyzed hydrogen-deuterium exchange occurs at the positions adjacent to the heteroatom for 4-thiapyrone (3), N-methyl-2-pyridone (9), 4-methoxy-N-methylpyridinium fluoroborate (19), and 1,3-dimethyl-4-pyrimidonium fluoroborate. The rates of exchange, relative to that of N-methyl-4-pyridone (1) in deuterium oxide at 100°, are for 3, 104.8 (deuterium oxide at 100°); 9, 10-0.8 (deuterium oxide at 100°); and 19, 105.3 (deuteriomethanol at 40°). Attempts to observe isotopic exchange at the corresponding positions in 2-thiapyrone, 2-pyrone and 4-pyrone led to substrate decomposition. Hydrogen-deuterium exchange at the 2 position of 3-methyl-4-pyrimidone and 1-methyl-4-pyrimidone in deuterium oxide at 100° is zero order in base as previously reported.6 These results are interpreted qualitatively in terms of ylide intermediates. © 1969, American Chemical Society. All rights reserved.