1.3.5- Triazine-2,4-diones, 5,6-dihydro

Dihydro 6 imino-2,4(l,3H)-s-triazine-dione. See Ammelide in Vol 1, p A273-L... 

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 1,2,4-triazine ring of 3,4-dihydro-2-methyl-1,2,4-triazino[3,2-6]-quinazoline-3,10-dione (622) was formed when 3-amino-2-(substituted amino)quinazolin-4-one (621) was cyclized with ethyl pyruvate in acetic acid (86JHC833). 

Data on the structures of monocyclic dihydro- or hexahydro-1,2,3-triazines, on 1,2,3-triazine tV-oxides and 1,2,3-triazinones are not yet available. From studies on the one-electron reduction of the tetrahydro-l,2,3-triazinium salts (7) it was concluded that the heterocyclic ring is flexible and not planar (80LA285). No detailed information on the structure of 3-benzyl-l,5-diphenyl-l,2-dihydro-l,2,3-triazine-4,6(3//,5f/)-dione (8) or of the 6-hydroxy-4-oxo-l,4-dihydro-l,2,3-triazinium hydroxide inner salts (9) seems to be available. 

CB445) and of the dihydro-1,2,3-triazine-4,6(3//,5//)-dione (8) have appeared (78CB2173). 

Treatment of l-benzoyl-6-methyl-l,6-dihydro-l,2,4-triazine-3,5-dione (126) with bases led to the 5-phenyl-1,2,4-triazolin-3-one (127) (03JA386). 

Dihydro-1,2,4-triazine-3,5 (2H,4H )-dione (139) rearranges with aldehydes, with which they form N-aminoimidazoledione derivatives (140) (68CCC2087). 

From the reaction of 6-phenyl-l,2,4-triazine-3,5-dione (157) with phenylmagnesium bromide, 5,6-diphenyl-1,2,4-triazin-3-one (27), 3,5,6-triphenyl-l,2,4-triazine (147), 3,3,5,6-tetraphenyl-2,3-dihydro-l,2,4-triazine (158), 2,4,6-triphenyl-l,3,5-triazine (148) and 2,4,4,5-tetraphenylimidazole (149) were isolated (71JPR699). From the results obtained in the reaction of 3,5,6-triphenyl-l,2,4-triazine (147) with phenylmagnesium-bromide it can be supposed that the last two compounds were formed via the intermediate formation of (147). 

Alkylation of l,2,4-triazine-3,5-dione (33 R = H) with dimethyl sulfate at 135-145 °C without a base afforded l-methyl-5-oxo-l,2,4-triazin-3-olate (185), the structure of which was proved by hydrogenation to be the dihydro compound (186) (73CCC934). 

Alkylation and acylation of 6-halo-l,2,4-triazine-3,5-diones yields 2- and 4-alkylated and -acylated derivatives. With trimethylchlorosilane they afford the 6-haIo-3,5-bis(trimethylsilyloxy)-l,2,4-triazines. l,6-Dihydro-l,2,4-triazine-3,5-diones (204) are acylated at N-l and N-2 and the diacylated product (205) can then be methylated by diazomethane at N-4 to afford compound (206) (63CCC2527). 

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). 

The cyclization of a-hydrazono oximes (635) with orthocarboxylates is an excellent way of preparing 1,2,4-triazine 4-oxides (636) (73TL1429,7lLA(750)12,77LA1713). Using aldehydes or ketones instead of orthoesters provides 2,3-dihydro derivatives (637 Scheme 22) (75S794). Cyclization of a-hydrazonocarboxamides (638) with carbonic acid derivatives such as ethyl chloroformate affords l,2,4-triazine-3,5-diones (639) (68M1808). The a-hydrazonocarboxamides (638) can be prepared by the reaction of diazonium salts with a-activated acetamides such as cyanoacetamide as shown. 

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). 

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). 

Ammelide 6-Amino-s-triazine-2,4 diol or 3,6-Dihydro-6-imino-s-triazine-2,4( 1H, 3H)-dione (called in Beil 4,6-Dioxo-2-imino-hexahydro-1.3.5-triazin Isocyaniirsaure-monoimid 2.4-Dioxy-6-amino-1.3.5-triazin or Melanurensaure)... 

Hydrazono-l,l,l-trifluoroalkan-2-ones (4) react with aldehydes in the presence of aqueous ammonia to yield 5-trifluoromethyl-2,3-dihydro-1,2,4-triazines which can be oxidised to give 5-trifluoromethyl-l,2,4-triazines (5) or 5-trifluoromethyl-2,5-dihydro-5-hydroxy-1,2,4-triazines (6) [94H(39)155], whilst hydrazines react with a-lactams to give 1,2,4-triazine-3,6-diones [95JOC4121 95JOC5992] (Scheme 3). 

Interaction of 8a with ethylchloroacetate in methanolic sodium methoxide leads to cyclocondensation with elimination of EtOH and HC1, affording the triazine-3,14-dione derivative (14), while 8a was reacted with alcoholic CS2-KOH to give 14-methyl-2,3-dihydro-13-oxo-2H,13H,14H-[l]Benzopyrano [3/,4/ 5/,6/]pyrano[3,2-e]-[l,2,4]triazolopyrimidine-2-thione (15) (Scheme 5). 

Dihydro-2iT-thiazolo[2,3-c][l,2,4]triazine-3,4-dione rearranges in dilute base to give an unstable acid which decarboxylates on acidification of the sodium salt to give 5,6-dihydrothiazolo[2,3-c]-s-triazole (equation 68) (81CB1200). Kinetic evidence has been put forward in favor of covalently hydrated intermediates in the acid-catalyzed rearrangement of triazolo[4,3-a]pyrazines to 1H-imidazo[2,1 -c]-s-triazoles. The intermediate triazole has been isolated and characterized (equation 69) (72JCS(P2)4). 

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