Mstract
-The condensation of ethyl urcido-oxyacetatc. O-methyl and O-bcnxylhydroxyurca with aoztylacetonc in cthanolic hydrogen chloride was found to bc a facile reaction which led to Icarbcthoxymcthoxy. 1 mcthoxy and 1 -bcnzyloxy-1 .2-dihydro-4.6dimethyl-2-oxopyrimidinc rcspeo tively. The N-rnethoxy (lb) and N-benzyloxy (Ic) dcrivativa could be transformed with 27% HBr in curtic acid to l,2dihydro-I.6dimcthyl-l-hydroxy-2-oxopyrimidine (III). Hydroxyurca gave with ooecylaatonc only a small yield of the N-oxide (III). Dissociation constants. IR and UV spectra in various hydrogen ion concentrations waz used to elucidate the tautomric structure of these pyrimidine-N-oxide dcrivativa. PYRIMIDINE-N-OXIDES are generally prepared by oxidation of pyrimidines by hydrogen peroxide' or by peracids. * Klotzerj used O-methyl and O-bcnzylhydroxyurea in the preparation of N-alkoxy derivatives of uracil, aminouracil, barbituric acid, cytosine and thyminc by basic catalysis of sodium ethoxide.
In the present work N-alkoxy derivatives of 1,2dihydro4,6dimethyl-2_oxopyrimidine were prepared by a smooth acid catalysed' condensation. The condensation products are obtained as their hydrochloridcs (I) in about S&907; yield, from acctylacetone and hydroxyurea derivatives in 610% ethanolic hydrogen chloride. Ring closure takes place within a few minutes, since complete crystallization of the products could be obtained after 20 minutes.
When ureido-oxyacctic acid6 was used, esteritication occurred prior to condensation resulting in the ester la which is obtained from ethyl ureido-oxyacetate.
In iht absence of acetylacetone, urcido-oxyacetic acid underwent, under the same conditions, in a few minutes complete csterification.
The fact that these oxopyrimidine derivatives give stable hydrochloridcs is consistent with other 2-oxopyrimidincs. a The hydrochlorides melt with decomposition accompanied by dark colouration; the simple alkoxy derivatives lb and Ic become dark violet, and the carbcthoxymethoxy derivative Ia gets a deep red colour in the range of the melting temperature. By neutralization with sodium bicarbonate the free l-aLkoxy-I.2dihydro-4,6dimethyl-2-oxopyrimidincs (II) could be obtained.