Acid catalysed condensation of ureido-oxy compounds with acetylacetone. Synthesis and properties of N-alkoxy and N-hydroxy derivatives of 1,2-dihydro-4,6-dimethyl-2-oxopyrimidine

The condensation of ethyl ureido-oxyacetate, 0-methyl and 0-benzylhydroxyurea with acetylacetone in ethanolic hydrogen chloride was found to be a facile reaction which led to 1-carbethoxymethoxy, 1-methoxy and 1-benzyloxy-1,2-dihydro-4,6-dimethyl-2-oxopyrimidine respectively. The N-methoxy (Ib) and N-benzyloxy (Ic) derivatives could be transformed with 27% HBr in acetic acid to 1,2-dihydro-4,6-dimethyl-1-hydroxy-2-oxopyrimidine (III). Hydroxyurea gave with acetylacetone only a small yield of the N-oxide (III). Dissociation constants, IR and UV spectra in various hydrogen ion concentrations were used to elucidate the tautomeric structure of these pyrimidine-N-oxide derivatives.