AbstractOn treatment with liquid ammonia at −33° the quaternary pyrimidinium saltsi.e.4‐ethoxy‐1‐ethyl‐ (1) and 4,6‐diethoxy‐1‐ethyl‐pyrimidinium tetrafluoroborate (3) undergo amino‐de‐ethoxylation, yielding 1,4‐dihydro‐1‐ethyl‐4‐imino‐pyrimidine hydrogen tetrafluoroborate (7) and a mixture of 1,4‐dihydro‐6‐ethoxy‐1‐ethyl‐4‐imino‐ (9) and 1,6‐dihydro‐4‐ethoxy‐1‐ethyl‐6‐imino‐pyrimidine hydrogen tetrafluoroborate (11), respectively.1HNMR and13CNMR spectroscopic evidence is presented for the fact that compounds 1 and 3 easily give σ‐adducts at position 2. Using15N‐labelled ammonia it was shown that in these amino‐de‐ethoxylation reactions the substitution at C(4) or C(6) does not involve ring opening but probably occursviaan SN(AEn) process. Reaction of 4‐ethoxy‐1‐ethyl‐2‐phenyl‐ (2), 6‐ethoxy‐1‐ethyl‐4‐phenyl‐ (4), 4,6‐dimethoxy‐1‐ethyl‐2‐phenyl‐ (5) and 4,6‐dimethoxy‐1‐ethyl‐2‐methyl‐pyrimidinium tetrafluoroborate (6) with liquid ammonia gives besides the amino‐de‐ethoxylation product degenerate ring transformations leading to theN‐de‐ethylated products14–16and 4(6)‐(ethylamino)pyrimidines17‐19. The salt11and 1,6‐dihydro‐1‐ethyl‐6‐