Pyrimidine reactions. Part XXV. Synthesis and piperidinolysis of some simple fluoropyrimidines

2-Fluoropyrimidine and its 4-methyl and 4,6-dimethyl derivatives are made by diazotization of the corresponding aminopyrimidines in fluoroboric acid. 4-Fluoro-2-methylpyrimidine, its 6-methyl isomer, and 4-fluoro-2,6-di-methylpyrimidine result from treatment of appropriate trimethylpyrimidin-4-ylammonium chlorides with aqueous potassium hydrogen difluoride. Second-order rate constants for piperidinolyses of the fluoropyrimidines and of 2-bromo-, 2-iodo-, 4-chloro-5-methyl-pyrimidine indicate that the fluoropyrimidines react 60–200 times faster than other (corresponding) halogenopyrimidines at the same temperature. The u.v. and 1H n.m.r. spectra are recorded and discussed.