1.2.4- Triazin-5-ones, 3-thioxo-, reaction

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

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. 

The transformation of one hetero substituent into another is a reaction frequently observed in the 1,2,4-triazine series. Oxo group transformations are indicated in Scheme 8. They can be transformed into thioxo groups by phosphorus pentasulfide or Lawesson s reagent. Pyridine seems to be the best solvent for the phosphorus pentasulfide reaction and a small amount of water (0.1% or less) seems to improve results. An oxygen in the 5-position is more easily replaced than one in the 3- or 6-position. Transformation of the oxo (hydroxy) group into a chloro substituent is achieved by phosphorus oxychloride, phosphorus penta-chloride, or thionyl chloride and DMF. In this reaction also the oxygen is most reactive in the 5-position. 

Reaction of 4-aryl-3-methylthio-l,2,4-triazin-5-ones (342) with hydrazine led to 4-amino-3-arylamino-l,2,4-triazin-5-ones (343) instead of the expected 4-aryl-3-hydrazino derivatives (344). This is explained by nucleophilic attack of the hydrazine at the 5-position, ring opening and subsequent reclosure. The same result was obtained when 4-aryl-3-thioxo-... 

The cyclization of a-hydrazinohydrazones (653) with ketones has been used for the synthesis of 4-amino-2,3,4,5-tetrahydro-l,2,4-triazines (654), and their reaction with phosgene affords 4-amino-4,5-dihydro-1,2,4-triazin-3-ones (655) (78HC(33)189, pp. 608, 656). 3-Thioxo-l,2,4-triazine-5,6-dione (657) was obtained when oxamohydrazide (656) reacted with thiophosgene (76ACS(B)7l). 

The reaction of 2-amino-2-selenazoline (34) and ethoxycarbonyl isothiocyanate affords 4-thioxo-2,3,6,7-tetrahydro-4/7-selenazolo[3,2-<2][l,3,5]triazin-2-one (99). Phenyl isothiocyanate and (34) give the 1,3,5-triazine derivative (100 Scheme 44) (74JOC1819,69T191). 

Reaction of the dithione 176 with ethyl chloroacetate gives 7H-6-thioxo-5,6-dihydrothiazolo[3,2-6]-[l,2,4,5]-triazin-3(2//)-one (177) and a... 

Most dihydro-l,2,4-triazinones can be converted into the corresponding thiones, and into chloro-dihydrotriazines, and they can be alkylated by the usual methods. These reactions are also known for the diones. As was mentioned earlier, in these reactions the 5-position is the most reactive. Treatment of 1,2,4-triazine-3,5-diones (258) with phosphorus pentasulfide leads firstly to the 5-thioxo-4,5-dihydro-l,2,4-triazin-3-ones (259), and then to the l,2,4-triazine-3,5-dithiones (260). Further reactions reported for l,2,4-triazine-3,5-diones (258) are bromination in the 6-position to give (261), replacement of one (262) or both oxygens by chlorine (263) on reaction with SOCI2,... 

From the reaction of 6-p-chlorostyryl-3-thioxo-3,4-dihydro-l,2,4-triazin-5(2F/)-one (271) with phenylmagnesium bromide a mixture of seven products was isolated. These were separated and identified as 6-/ -chlorostyryl-5-phenyl-l,2,4-triazine-3(2/f)-thione (272), 6-p-chlorostyryl-5,5-diphenyl-4,5-dihydro-l,2,4-triazine-3(2//)-thione (273), the open-chain compounds (274)- 276), thiosemicarbazide and sulfur (Scheme 49). Mechanisms for the formation of these products were suggested <84JHC905>... 

Reaction of 6-amino-5-thioxo-4,5-dihydro-1,2,4-triazin-3(2//)-one (328) with haloacetophenones provides the 7-aryl-2,8-dihydro-3//-[l,4]thiazino[2,3-e]-l,2,4-triazin-3-ones (329) (Equation (40))... 

Thioxo-3,4-dihydro-l,2,4-triazin-5(2//)-ones (330) and 2,4-dinitro- or 2,4,6-trinitro-chloro-benzene (331) afford [l,2,4]triazino[3,2-6]benzothiazol-3-ones (333) or the 5-arylated intermediates (332), depending on the reaction temperature (Scheme 60) <88LA1089>. 

Reaction of 4-amino-6-methyl-3-thioxo-3,4-dihydro-l,2,4-triazin-5-one (339) with isocyanates in DMF yields 4Ff-l,3,4-thiadiazolo[2,3-c]l,2,4-triazin-4-one derivatives (340) (Equation (43))... 

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