Partially fluorinated heterocyclic compounds. Part 22. The preparation of allyl 2,5,6-trifluoropyrimidin-4-yl ether and related compounds and a study of their Claisen rearrangement reactions. A new route to 5-fluorouracil and barbituric acid derivatives

Abstract

Vapour phase thermolyses of allyl 2,5,6-trifluoropyrimidin-4-yl, (1), 2,5-difluoro-6-methoxypyrimidin-4-yl, (5), 2,5-difluoropyrimidin-4-yl, (6), and 5,6-difluoro-2-methoxypyrimidin-4-yl, (7), ethers gave the Claisen rearrangement products (2), (17), (18), and (20) respectively, in which N-3 is the migration terminus, but the 2-allyl derivative (10) was inert. In other thermolyses with allyl 5-fluoropyrimidin-4-yl ethers where a preliminary reaction results in the localisation of the C-4 to C-5 double bond, C-5 is the migration terminus: barbituric acid derivatives (28) and (26) are formed from (5) and allyl 2,5-difluoro- 6-hydroxypyrimidin-4-yl ether (13) respectively after hydrolysis of each rearrangement product and (14) also gave (26); 2,4-diallyl-5-fluoro-6-methoxypyrimidine (11) gave (29)(with the loss of CH₃) and 2,4,6-triallyloxy-5-fluoropyrimidine (12) was isomerised to (30). Allyl 2,6-dimethoxy-5-fluoro- pyrimidin-4-yl ether (8) gave both N-3 and C-5 migration termini products (21) and (33) respectively. Hydrolysis of (2), (17), and (18) gave the 5-fluorouracil derivatives (22), (23), and (24) respectively.