Chemistry of Pyrimidine. 2. Synthesis of Pyrimidine N-Oxides and 4-Pyrimidinones by Reaction of 5-Substituted Pyrimidines with Peracids. Evidence for Covalent Hydrates as Reaction Intermediates

Article abstract of DOI:10.1021/jo00217a012

The reaction of 5-substituted pyrimidines with peracids has been found to take divergent pathways depending on the presence or absence of a strong acid.Reaction of 5-bromo- (1) or 5-methoxypyrimidine (6) with m-chloroperbenzoic acid afforded the corresponding N-oxides in 29percent and 70percent yields, respectively.The formation of an N-oxide was not observed when either 1 or 6 was treated with 40percent peracetic acid in the presence of 1 equiv of sulfuric acid.In the case of 1, the product was 5-bromo-5(3H)-pyrimidinone (3), formed in 70percent yield.From 6, two products, 5-methoxy-4-(3H)-pyrimidinone (8) and 4(5)-carbomethoxyimidazole (9), were formed in a combined yield of 70percent (3:2 ratio of 8 to 9).The N-oxides were demonstrated to be stable to the above reaction conditions and are therefore not intermediates in the formation of 3, 8, or 9.Evidence for the existence of covalent hydrates makes it reasonable to suggest their formation as reaction intermediates.