Substituted pyrimidines. II. 1,3‐Dimethylisocytosine and related compounds

1,3‐Dimethyl‐1,2‐dihydro‐2‐imino‐4(3 H )pyrimidinone (1,3‐dimethylisocytosine) was prepared by methylation of 2‐amino‐3‐methyl‐4(3 H )pyrimidinone and was degraded in alkaline solution to a mixture of 3‐methyl‐2‐methylamino‐4(3 H )pyrimidinone, 1,3‐dimethyl‐2,4‐(1 H ,3 H )pyrimid‐indione, 2‐methylamino‐l‐methyl‐4(1 H )pyrimidinone, 1‐methyl‐2,4‐(1 H ,3 H )pyrimidindione and 3‐methyl‐2,4‐(1 H ,3 H )pyrimidindione. Thiation of the title compound gave both 1,2‐dihydro‐1,3‐dimethyl‐2‐thio‐4(3 H )pyrimidinone and 1,3‐dimethyl‐2,4‐(1 H ,3H)pyrimidinedithione. The title compound is a tautomerically fixed pyrimidine and its uv spectra were compared with related compounds, notably 3‐methyl‐2‐dimethylarnino‐4(3 H )pyrimidinone which is also tautomerically fixed.