Triazolo triazine, rearrangement

Diazotization of 5-amino[l, 2,3]triazole 692 afforded (88BSB179) triaz-olo[l, 5-i>][l, 2,4]triazine 694 as a result of a Dimroth rearrangement of the initially formed isomeric structure triazolo[5,l-c][l,2,4]triazine 693. Molecular structure of 694 was determined by single X-ray diffraction (Scheme 146). 

Amino-4-cyano-4-methyl-4/f-l,2,3-triazole (291) reacts with formamidine at room temperature to give the substituted l,2,3-triazolo[l,5-a]-l,3,5-triazine (293) via a translocative rearrangement of the presumed intermediate (292) (Scheme 56) <85JOC4986>. 

The s-triazolo[4,3-a][l,3,5]triazine (78) undergoes a Dimroth-type rearrangement on heating with excess dimethylamine (Scheme 49) (73JHC231). Kobe et al. have reported a... 

The condensation of 3-(substituted)-l,2,4-triazoles with an A-cyanocarbonimidate at high temperatures gives (1,2,4]triazolo 1,5-a [ 1,2,3]triazines (34) which are converted to other such products by standard metatheses. At lower temperatures l,2,4Jtriazolo[4,3- ][l,3,5]-triazines (35) can also be obtained which rearrange to the more stable (1,5-a] isomers on heating. Cyclisation of the hydrazides (36) also leads to [1,5-a] fiised triazines (Scheme 20) [95JCS(P1)801],... 

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). 

In addition to the Dimroth rearrangement of [l,2,4]triazolo[3,4-c][l,2,4]triazines discussed in the last section, derivatives of (42) would probably be accessible by the general application of a special case which involved the reaction of l-acetonyl-5-chloro-l,2,4-triazole (356) with hydrazine to produce the dihydro compound (357). Lead tetraacetate oxidation of (357) formed (358) (77JOC1018). 

Treatment of 3-amino-5-hydrazino-l,2,4-triazole with benzil produced 2-amino-6,7-diphenyl-[l,2,4]triazolo[5,l-c][l,2,4]triazine via either direct formation involving cycliz-ation on the triazole N-1 or attack at N-4 of the triazole to yield the [3,4-c] compound which rearranged to the [5,1-c] isomer (76JCS(P1)1492). Ring closure of 3,4-diamino-1,2,4-triazines with carboxylic acids is also a route to various [l,2,4]triazolo[5,l-c][l,2,4]triazines (64CB2173). 

The diazotization of 5-amino-4-carbamoyl-l-(a-styryl)-l,2,3-triazole (30) gave 5-phenyl-1.2,3-triazolo[l,5-h][l,2,4]triazine-3-carboxamide (32) as a result of rearrangement of the initially formed 7-phenyl-l,2,3-triazolo[5,J-c][l,2,4]triazine-3-carboxamide (31). Compound 32 is favored thermodynamically and its structure was confirmed by an X-ray crystallographic study (88BSB179) (Scheme 10). 

Highly nitrogenous heterocycles such as l,2,4-triazolo-l,3,5-triazines have been shown to rearrange upon treatment with excess base. 5,7-Bis(dimethylamino)-3-(methylthio)-l,2,4-triazolo[4,3-a][l,3,5]triazine 51 was isomerized to 53 via isolatable guanidine intermediate 52 in the presence of excess anhydrous dimethylamine, pyrrolidine or aniline in absolute ethanol at 85 This reaction was also shown to go forward under acidic conditions, although a mixture of 52 and 53 was recovered in the process. 

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