1.2.4- Triazine-3-thion-5-ones

The electrochemical oxidation of catechols in the presence of 6-methyl-1,2,4-triazin-3-thion-5-one and 4-amino-6-methyl-l,2,4-triazin-3-thion-5-one as nucleophiles in aqueous solutions provided an efficient electrosynthesis of thiazolo[3,2-6][l,2,4]triazin-7-one and l,2,4-triazino[3,4-/)J 1,3,4-thiadiazinc derivatives respectively <06TL1713> <06TL8553>. 

Similarly, the reaction of carbethoxyisothiocyanate (EtO CNCSl with 2-aminoselenazo ine leads to 2.3,6.7-tetrahydro-4H-selenazoio[3.2-fl]-s-triazin-2-one-4-thione Scheme 62 (66). 

Formation constants of Ag(I) complexes with 5,7-dimethyl-4a,7a-diphenyloctahydroimidazo[4,5-e][triazin-6-one-3-thione was determined potentiometrically (79MI2). 

Triazine-3-ones and triazine-3-thiones can also be reduced in two consecutive steps leading to the corresponding dihydro and tetrahydro derivatives. However, according to the experimental conditions, a ring contraction can occur at the second step [250]. 

As with 5-alkyl-l,2,4-triazin-3-ones, so also 5-alkyl-l,2,4-triazine-3-thiones (42) display proton tautomerism between the alkyl group and a ring nitrogen, as shown by H NMR spectroscopy (68TL2747). 

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. 

Amino-l,2,4-triazines (86) react with phenylhydrazine to afford 2-phenyl-l,2,3-triazoles (135) (60MI21900). 3-Thioxo-l,2,4-triazin-5-ones (76) are transformed into 1,2,4-triazole-3-thiones (136) by treatment with sodium methoxide (72BSF1511). Treatment of compound (137) with acetic anhydride in the presence of sulfuric acid led to the isolation of the pyrazole (138) (10JA1499). 

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-... 

Reaction of 5,6-diphenyl-1,2,4-triazin-3-one (215) or 5,6-diphenyl-l,2,4-triazine-3-thione (216) with benzene under Friedel-Crafts conditions led to the isolation of 5,5,6-triphenyl-4,5-dihydro-l,2,4-triazin-3-one (217) and -3-thione (218) respectively (76IJC(B)273). Reacting under similar conditions (C6H6/A1C13) the 6-styryl compounds (219-221) are converted into the corresponding 6-(2,2-diphenylethyl) derivatives, e.g. (222) from (219) (75IJC1098). 

The reaction of a-amino ketones (508d) with thiosemicarbazides (761) affords 3-amino-4,5-dihydro-l,2,4-triazines (762) and the dihydrotriazine-3-thiones (763) (57MI21900). 2,2-Dimethyl-3-dimethylamino-2i/-azirine (764) reacts with benzohydrazides (765 R = Ar) via the open-chain intermediates (766) to give 3-aryl-6-dimethyIamino-2,5-dihydro-l,2,4-triazines (767 R = Ar). With ethyl carbazidate (765 R = OEt) the corresponding triazin-3-one (768) is formed (78HCA2419,78C332). 

Many 1,2,4-triazines form complexes with metal ions and can be used for their determination. Thus, 3- and/or 5-(2-pyridyl)-substituted 1,2,4-triazines (e.g. 820) can be used for the determination of iron (II), cobalt(II), nickel(II), zinc(II) and copper(I) ions, thallium and palladium ions can be analyzed by 6-phenyl- (821a) and 5,6-diphenyl-l,2,4-triazine-3-thione (821b), while osmium can be determined by 3-thioxo-l,2,4-triazin-5-one (822), 3-thioxo-dihydro-l,2,4-triazin-5-one (823), 6-mercapto-l,2,4-triazine-3,5-dione (824a), 6-mercapto-5-thioxo-l,2,4-triazin-3-one (824b) and 3,5-dithioxo-l,2,4-triazine-6-carboxyl-ates (825) <78HC(33)189, p. 1004). 

Alkyl-hexahydro-l,3,5-triazin-2-ones are prepared by the reaction between urea, formaldehyde and primary amines (73S243). The intermediate polycondensate (87) undergoes intramolecular cyclization on heating to yield the desired product (Scheme 52). By using substituted ureas (or thioureas) and/or different aldehydes, a wide variety of N-substituted 5-alkyl-hexahydro-l,3,5-triazin-2-ones (or 2-thiones) may be prepared. 

Mesomeric 1,3,5-triazine-dione, -one-thione and -dithione betaines may be synthesized from N,N -disubstituted acetamidines (Scheme 73) (75JHC187). Huffman and Schaefer have reported the synthesis of the triazine 1-oxide (137) in 45% yield from methyl N-cyanoacetimidate and benzamidoxime (equation 70) (63JOC1816). 

Reduction of the pyrano-l,2,4-triazin-3-one (132) using zinc powder in AcOH gave the dihydro compound (134) (85%). Analogous reduction of pyrano-l,2,4-triazin-3-thione (151) delivered com-... 

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