Syntheses and properties of 4,6‐dimelhyl[1,2,5]oxadiazolo[3,4‐ d ]pyrimidine‐5,7(4 H ,6 H )dione 1‐oxide

New convenient syntheses of 4,6‐dimethyl[1,2,5]oxadiazolo[3,4‐ d ]pyrimidine‐5,7(4 H ,6 H )‐dione 1‐oxide (I) from 1,3‐dimethyl‐6‐hydroxylaminouracil by means of nitrosative and nitrative cyclizations are described. Compound I was converted into 4,6‐dimethyl[1,2,5]oxadiazolo[3,4‐ d ]pyrimidine‐5,7(4 H ,6 H )dione [4,6‐dimethyl‐5,7(4 H ,6 H )furazano[3,4‐ d ]pyrimidinedione] by refluxing in dimethylformamide. Transformation of I to 1,3,7,9‐tetramethyl‐2,4,6,8(1 H ,3 H ,7 H ,9 H )pyrimido[5,4‐g]pteridinetetrone and/or 1,3,6,8‐tetramethyl‐2,4,7,9(1 H ,3 H ,6 H ,8 H )pyrimido[4,5‐g]pteridinetetrone is described.