3-Thioxo-1,2,4-triazin-5 -ones

All 1,2,4-triazines containing a thioxo group either in the 3-, 5- or 6-position are alkylated by methyl iodide or dimethyl sulfate at the sulfur if this is possible. This observation is reported for l,2,4-triazine-3-thiones, -5-thiones, -3,5-dithiones, -3,5,6-trithiones, 3-thioxo-1,2,4-triazin-5 -ones, 5 -thioxo-1,2,4-triazin-3-ones, 5-amino-1,2,4-triazine-3-... 

For the debromination of 6-bromo-l,2,4-triazine-3,5-diones (312), both sodium in ammonia and butyllithium have been used (58JA976,67RRC913). Other methods of obtaining an unsubstituted ring position include desulfurization with Raney nickel of 3-thioxo-1,2,4-triazin-5-ones (187) to the triazin-5-ones (313) (73BSF2126), and treatment of the 3-sulfonylhydrazino-1,2,4-triazines (314) with a base to afford the compounds (107) (55MI21900). 

Triazin-5-One, 3-thioxo-alkylation, 3, 408 desulfurization, 3, 416 mass spectra, 3, 397 metal complexes, 3, 456 methylation, 3, 408 reactions... 

Thioxo-l,2,4-triazin-5-ones and hydrazonyl halides react together in the presence of triethylamine in dichloromethane to yield l,2,4-triazolo[4,3-ftHl,2,4]-triazin-5-ones 81 <95M105 96CA(124)317107>. 

For the synthetic studies on the bicyclic 6-6 systems 1-3, with one ring junction nitrogen and five extra heteroatoms, refer to CHEC-II(1996) <1996CHEC-II(8)743>. In the studies of the newly available compounds, a one-pot procedure for the synthesis of [l,2,4]triazino-[4,3- ][l,2,4,5]tetrazine 4 derivatives is discussed below. Refluxing of hydrazonoyl halides 10 in chloroform (or ethanol) in the presence of triethylamine for 6h with either 4-amino-2,3-dihydro-6-substituted-3-thioxo-[l,2,4]triazin-5(4//)-ones 8 or 4-amino-3-methylthio-6-substituted-[l,2,4]-triazin-5(4//)-ones 9 yielded compounds 4 (Equation 1) <2000JPR342>. 

The pyrolysis in the gas phase of 4-benzylidenamino- and 6-styryl- l, 2,4-triazinc-3,5(2//, 4//)-diones and 6-styryl-2,3-dihydro-3-thioxo-l,2,4-triazin-5(4//)-ones has been studied <06T1182 06T6214>. 

The triazine ring could be formed by reaction [82S853 83BSF(2)226] of alkyl (2-aryl-4-thioxo-3,4-dihydro-2//-quinazolin-3-yl)acetates 477, prepared from 476, with hydrazine to yield 6-aryl-2,4-dihydro[l,2,4]tria-zino[4,3-c]quinazolin-3-ones 478. 

Pyrazolo[l,5-a]-l,3,5-triazines are also obtained from acyclic intermediates. Thus, treatment of cyanoethanoic acid hydrazide with benzoyl isothiocyanate affords the corresponding benzoylthiosemicarbazide, which cyclizes into 4-thioxo-2-phenyl-3,4,6,7-tetrahydropyrazolo[l,5-a]-l,3,5-triazine-7-one upon treatment with 5% potassium hydroxide (84JHC781). 

The unsubstituted 5-thioxo-l,2,4-triazin-3-one (36) shows an UV spectrum which is similar to those of the 2-methyl, 4-methyl and 2,4-dimethyl derivatives, implying that the 2//,4//-tautomeric form is the predominant one (62CCC1886). 5-Methylmercapto-1,2,4-triazin-3-one (37) and its 2-methyl derivative (38) show completely different spectra. Similar results have been obtained for 3-thioxo-l,2,4-triazin-5-ones (61CCC986, 68CCC2962, 62CCC1886). 

The addition of methoxide ion to 3-methylthio-l,2,4-triazine-5-ones (78) leading to (98) and then to (99) is reported by Piskala (75CCC2340). Hydrazine adds to the C=0 double bond of 3-thioxo-l,6-dihydro-l,2,4-triazin-5-ones (100) (70BSF1606). 

Complete destruction of the heterocyclic ring of 1,2,4-triazines on prolonged treatment with aqueous acids is reported for l,2,4-triazin-3-ones (84), l,2,4-triazine-3-thiones (85), 3-thioxo-l,2,4-triazine-5,6-diones (115), 1,2,4-triazine N-oxides, and l,2,4-benzotriazin-3-ones (116). This is a fairly general observation in 1,2,4-triazine systems. 

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