1.2.4- Triazines, 1,2,3,6-tetrahydro

In addition to these aromatic 1,2,4-triazines, X-ray crystallographic data have been published for a large number of 1,2,4-triazinones, 1,2,4-triazinediones, dihydro-1,2,4-triazines, tetrahydro-1,2.4-triazines or condensed 1,2,4-triazines.9,10... 

Heating of this latter compound with an excess of phenyl isothiocyanate in acetonitrile (65) leads to 2-phenylimino-3-phenyl-4-thioxo-se enazole[3.2-a]tetrahydro-s-triazin (Scheme 61). 

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). 

H-Pyrazino[l,2-a][l,3,5]triazine, 2-amino-8-methyl-4,9-dioxo-cis-6,7-diphenyl-6,7,8,9-tetrahydro-... 

According to the triazine nomenclature, 5-azauracil is 2,4-dioxo-l,2,3,4-tetrahydro-l,3,5-triazine (2). The subject index of Chemical Abstracts prefers s-triazine-2,4(lH,3H)-dione. Furthermore, some authors use a name derived from the lactim structure, 2,4-dihydroxy-s-triazine (3). The numbering of the substituents is the same for all these types of nomenclature. 

According to systematic triazine nomenclature, 6-azauracil is 3,5-dioxo-2,3,4,5-tetrahydro-1,2,4-triazine (42). The indexes of the Chemical Abstracts describe it as as-triazine-3,5(2H,4H)-dione. In addition ... 

In this connection the possibility of oxidation of these substances to the tetrahydro derivatives should be mentioned. It was made use of by Thiele and Bailey for the preparation of 6-methyl-3,5-dioxo-2,3,4,5-tetrahydro-l,2,4-triazine (6-azathymine) (46) and only recently by Grundman et al. for that of 6-azauracil (42). 

In continuing their previous work Bougault and Daniel observed that thiosemicarbazones of a-keto acids (51) also undergo a cyclization resulting in 3-thioxo-5-oxo-2,3,4,5-tetrahydro-l,2,4-triazines (52). In contrast with the cyclization of semicarbazones this cyclization... 

It was observed already by BougaulU that the reaction of 6-benzyl-3,5-dioxo-2,3,4,5-tetrahydro-l,2,4-triazines with alkyl halides in an alkaline solution yields a mixture of the 4-mono- and 2,4-dialkyl derivatives. This mixture of alkylation products can be readily sepa-... 

By comparing the dissociation constant of 6-azauracil and 6-aza-uridine with those or uracil and uridine, 6-azauridine is now considered to be 1-ribofuranosyl derivative (2-ribofuranosyl-3,5-dioxo-2,3,4,5-tetrahydro-l,2,4-triazine), The same was shown more exactly by comparing the UV and IR spectra and the dissociation constants of 6-azauridine with the two monomethyl derivatives of 6-aza-uracil," Enzymatic synthesis thus, proceeds, in the same way in natural bases and in their aza analogs. 

Thioxo-3-oxo-2,3,4,5-tetrahydro-l,2,4-triazine (4-thio-6-azauracil) (88) and 3,5-dithioxo-2,3,4,5-tetrahydro-l,2,4-triazine (2,4-dithio-6-azauracil) (89) w ere prepared by Hitchings et al. treating 6-aza-... 

Alkyl and 6-aryl derivatives of 3,5-dioxo-2,3,4,5-tetrahydro-l,2,4-triazine or of its thio analogs have been mentioned before in this review (e.g., Section II,B,2,a). Some of theih contained functional... 

Oxo 5-imino-2,S,J, 5-tetrahydro-l,, 4-triazine 6-Azacytosine) Substances of this type were not studied by the earlier workers, and the first representative of this group to be investigated was 3-oxo-5-imino-2,3,4,5-tetrahydro-l,2,4-triazine (122) which should bear the name 6-azacytosine. It was prepared by Falco et al. by treating 3-thioxo-5-oxo-2,3,4,5-tetrahydro-l,2,4-triazine (88) with alcoholic ammonia. Some iV-substituted derivatived were prepared anal-ogously. ... 

Ring-chain tautomerism was observed in a series of l,2,3,6-tetrahydro-l,2, 4-triazine 4-oxides 5 in nonpolar solvents (e.g., CCI4) by NMR spectroscopy. Depending on the nature of substituents R and R, the ratios of the cyclic form of 1,2,4-triazine 5a to the open-chain form of hydrazone 5b were found to be up to 45 55 (77ZOR2617). 

Hydrazino-3-methylbutan-2-one oxime reacts with aldehydes and ketones, resulting in l,3,4,6-tetrahydro-l,2,4-triazine 4-oxides 155 (77ZOR2617). 

The 1,2,4-triazine 4-oxides 55 were synthesized by the reaction of nitrones 158 (generated from a-hydroxylamino ketones and aldehydes) with an excess of hydrazine, followed by the oxidation of the intermediate 4-hydroxy-2,3,4,5-tetrahydro-l,2,4-triazines 159 with lead(TV) oxide (73KGS134). 

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