P. Chang, K. Chiang
1956
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Journal
Acta Chimica Sinica
Abstract
The method employed by Chang and Wu has been extended to the synthesis of various 2-substituted-5,6(4)-dihydroxypyrimidines. 1.The requisite β-keto-ester,ethyl α-benzyloxy-β-hydroxyacrylate(Ⅳ),was obtained in 79% yield by condensing ethyl benzyloxyacetate and ethyl formate in the presence of sodium methoxide in dry ether. 2.Ⅳ was caused to condense with various amidine derivatives to give:2,6(4)-dihydroxy- (Ⅴ),2-amino-6(4)-hydroxy-(Ⅵ),2-methyl-6(4)-hydroxy-(Ⅶ),2-thiol-6(4)-hydroxy-(Ⅷ)and 2-ethylthio-6(4)-hydroxy-5-benzyloxypyrimidine(Ⅸ).Desulfurization of Ⅷ or Ⅸ with Raney nickel yielded the 2-unsubstituted 6(4)-hydroxy-5-benzyloxypyrimidine(Ⅹ).The benzyl residue was not affected under this treatment. 3.Debenzylation of the above pyrimidines was effected readily by hydrogenolysis in the presence of Adams'palladous oxide catalyst.Thus,the following 5-hydroxypyrimidines were obtained:iso-barbituric acid [Ⅺ,2,5,6(4)-trihydroxypyrimidine],2-amino-(Ⅻ)and 2- methyl-5,6(4)-dihydroxypyrimidine(ⅩⅢ)as well as 2-unsubstituted 5,6(4)-dihydroxy- pyrimidine(ⅩⅣ). 4.Except that iso-barbituric acid(Ⅺ)and 2-amino-5,6(4)-dihydroxypyrimidine(Ⅻ)had been obtained by other synthetic routes,all the above pyrimidines are not known previously and they are high-melting crystalline solids of considerable stability. 5.The fact that the 5-hydroxy group is aromatic in character is reflected by the color reactions developed by all these compounds with ammoniacal ferric chloride,barium hydroxide and phosphomolybdic acid in aqueous solution.Considerable interest is attached to the observation that these pyrimidines are able to decolorize 2,6-dichlorophenolindophenol just as ascorbic acid and 2-substituted 4,5,6-trihydroxypyrimidines do as previously reported.The corres- ponding 5-O-benzyl derivatives do not show any of these color reactions. 6.The probable transformations involved in the decoloration of 2,6-dichlorophenolindo- phenol by 2-substituted and 2-unsubstituted 4,5,6-tri-and 5,6(4)-di-hydroxypyrimidines were discussed in the light of their enediol structure in analogy with,say,ascorbic acid.