4-amino-l,2,4-triazin-5-ones

Irradiation of 1,2,4-triazine 4-oxides (124) led to the deoxygenated products, and also, when position 5 was unsubstituted, to 1,2,4-triazoles (364) (76LA153). 4-Amino-l,2,4-triazin-5-ones (365) are photochemically deaminated. This has been demonstrated, in particular, with the 6-r-butyl-3-methylthio compound (8) which is used as a herbicide... 

Amino-l,2,4-triazin-5-ones (674) have been prepared by the reaction of a-acyl-hydrazonocarboxylates (672) or the chloro derivatives (673) with hydrazine. The chloroazines (673) with hydroxylamine afford 4-hydroxy-1,2,4-triazin-5-ones (675 Scheme 26) <78HC(33)189, p. 563). 

In a further [6+0] cyclization reaction, heating the acylhydrazonocarbohydrazides (759) for 25 h in boiling ethanol with sodium acetate affords 4-amino-l,2,4-triazin-5-ones (527) (79GEP2366215). Intermediates in reactions mentioned in earlier sections, which could in principle be isolated and cyclized in a separate operation, include compounds (454), (457), (465), (466), (470) and (475), among others. The l,2-bis(semicarbazone) (760) is cyclized... 

A 4-amino-l,2,4-triazin-5-one has been photochemically deaminated to give product 23, which has been identified by mass spectroscopy.429... 

Similarly, in 4-amino-6-i r7-butyl-3-methylthio-l,2,4-triazin-5(47/)-one, which is known as the widely used weedcontrolling agent metribuzin <1998M1869>, as well as in all 4-amino-l,2,4-triazin-5-ones studied, the 1,6-C=N bond is reduced first electrochemically, followed by reduction of the 2,3-C=N bond <2004M1777>. 

Research is in most cases a continuous process and takes place in small steps. To better understand the discovery of amicarbazone we should go back to the year 1964 when Dornow published the first examples of the hitherto unknown class of 4-amino-l,2,4-triazin-5-ones [25] (Fig. 10.4). 

Reduction of 4-amino-1,2,4-triazin-5-ones (291) affords compounds which were formulated (rather improbably) as 4-amino-5-hydroxy-3,4-dihydro-l,2,4-triazines (292)... 

Amino-l,2,4-triazine-5,6-diones (534), 4-amino-4,5-dihydro-1,2,4-triazines (535), 4-amino-5-imino-l,2,4-triazines (536) and 4,6-diamino-1,2,4-triazin-5-ones (537) were prepared by reaction of hydrazidines (526) with oxalates, a-bromo ketones, acyl cyanides (485) and thioxamidates, respectively (80UP21900). 

Amino-l,2,4-triazin-5(4//)-ones can be used as agrochemicals, in particular 4-amino-6-te/7-butyl-3-(methylsulfanyl)-l,2,4-triazin-5(4//)-one (11a, Sencor, Metribuzin), 4-amino-6-tert-butyl-3-(cthylsulfanyl)-1,2,4-triazin-5(4//)-one (lib, Ethyl Metribuzin, SMY1500) and 4-amino-3-methyl-6-phenyl-l,2,4-triazin-5(4//)-onc (12, Goltix, Metamitron).23... 

Similarly, reduction of pyrimido[5,4-e]-l,2,4-triazin-5-one 5 with sodium dithionite in acetic acid yields a mixture of 9-acetamido- (yield not reported) and a small amount of 9-amino-substituted purin-6(l//)-one.380... 

Amino-l,2,4-triazin-5(4//)-ones are biologically active some of them are used as herbicides, e.g. metribuzin 31 and metamitron 32. 

Sencor — see l,2,4-Triazin-5-one, 4-amino-6-t-butyl-3-methylthio-Senecio alkaloids structure, 7, 658 Senepoxide, 7, 192 Senkirkine conformation, 7, 703 structure, 7, 658 Sensitizing dyes... 

The reaction of 6-amino[l,2,4]triazin-5(2//)-ones or its thione derivatives 680 with acetic anhydride gave the 6-acetamido derivatives 681 and 682, respectively. Treatment with phosphorus pentasulfide in pyridine gave thiazolo[5,4-e][l,2,4]triazines 683 (84LA283 87AJC491) (Scheme 142). 

The reaction of 5-mercapto-6-amino-l,2,4-triazin-3-one 143 with a-haloketones gives the thiazino[2,3-r ]-l,2,4-triazines 144 shown in Equation (21), although the publication lacks further detail (yields, for example, are not given) and focuses upon the synthesis of other heterocyclic systems <2001PS205>. 

The isomeric l,2,4-triazin-5-ones also have herbicidal activity, and of these the 4-amino compounds stand out. Metribuzin (3) and metamitron (4) (68SAP6804409) possess excellent selectivity, the former being manufactured on a very large scale. Metribuzin can be synthesized from 3,3-dimethyl-2-oxobutyric acid (Scheme 3). 

The data obtained for 6-amino-3-methyl-l,2,4-triazin-5-one (17) show the surprising result that the non-ionic structure (17a) contributes little to the resonance while the ionic structures (17b-f) have to be considered in the crystalline state, which is probably due to the stabilization of these structures by hydrogen bonding or other crystal fields acting on this molecule. 

Amino-4-methyl-l,2,4-triazin-3-ones (43a) were shown to exist predominantly in the 5-imino forms (43b), due to the destabilization of the amino tautomer (43a) by the formal N=N double bond (64CCC1394, 65JCS5230). On the other hand, for 3-amino-4,6-dimethyl-l,2,4-triazin-5-one (44a) the predominance of the amino tautomer was proven and no imino tautomer (44b) could be detected. 

Phenylmagnesium bromide converts 3-amino-6-phenyl-l,2,4-triazin-5-ones (164) into 3-amino-5,6-diphenyl-l,2,4-triazines (165) (73JPR221). 

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-... 

Some new l,2,4-triazin-5-ones fused to 1,2,4-triazines 54, l,2,4-triazin-5-ones 55, 1,2,4,5-tetrazines 56 and l,2,4,5-tetrazin-3-ones 57 have been synthesized from 4-amino-6-styryl-3-thioxo-1,2,4-triazin-5(4//)-ones <03PS2055>. 

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