Dihydro-1,2,4-triazin-6(1H)-ones. III. Oxidation Products of 1-Methyl-3-phenyl- 4,5-dihydro-1,2,4-triazin-6(1H)-one

1-Methyl-3-phenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one (1) undergoes aerial oxidation to give a mixture of 1-methyl-3-phenyl-1,2,4-triazin-6(1H)-one (2) and 1-methyl-3-phenyl-1,4-dihydro-1,2,4-triazine-5,6-dione (3). The dehydro derivative (2) was cleanly prepared by the oxidation of (1) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (ddq). The dehydro derivative (2) underwent a surprising rearrangement to the triazole (12) upon oxidation with Oxone(R). Several attempts at unambiguous synthesis of the alpha-dicarbonyl derivative (3) were unsuccessful; it was obtained, together with the 1,4-dimethyl derivative (13) by methylation of 3-phenyl-1,4-dihydro-1,2,4-triazine-5,6-dione (4) with sodium hydride and methyl iodide.