Fused Pyrimidines. II. Synthesis and Oxidation of 3-Aminoisothiazolo [3, 4-d] pyrimidines

Reaction of 6-aminouracils (I) with alkyl or aryl isothiocyanates afforded 6-amino-5-substituted thiocarbamoyluracils (II), which were oxidized with bromine or hydrogen peroxide to afford 3-(substituted) aminoisothiazolo [3, 4-d] pyrimidin-4, 6-(5H, 7H)-diones (III). Alkylation of III afforded 3-(N, N-disubstituted) amino derivatives (V). Further oxidation of 1, 3-diethyl-3-dimethylamino-or-3-methylaminoisothiazolo [3, 4-d] pyrimidin-4, 6-(5H, 7H)-dione (Vb or IIIb) with hydrogen peroxide afforded 1, 3-diethyl-5-alkylcarbamoyl-5-hydroxybarbituric acid (Xa or Xb). Treatment of Xa with Raney nickel afforded 1, 3-diethyl-5-dimethylcarbamoylbarbituric acid (XII).