On the N‐ethylation of 4‐alkoxy‐ and 4,6‐dialkoxypyrimidines with triethyloxonium tetrafluoroborate

Reaction of 4‐alkoxy‐(1–4) or 4,6‐dialkoxypyrimidines (5–9) with 1 equivalent of triethyloxonium tetrafluoroborate yields 4‐alkoxy‐N‐ethyl (13–15) or 4,6‐dialkoxy‐N‐ethylpyrimidinium salts (10–12), respectively. With two or more equivalents of this reagent, rearrangement of N‐ethylalkoxypyrimidinium salts into 1‐ethyl‐3‐alkyl‐1,4(3,4)‐dihydro‐4‐oxopyrimidinium salts (16–22) takes place. These rearrangements can also be performed by heating. The mechanism of these rearrangement reactions is discussed.