6 -amino-1,2,4-triazolo tetrazine

The only known representative of 1,2,3,4-tetrazines (502) has been obtained with 81% yield on oxidation of l-amino-5-phenyl-l,2,3-triazolo[4,5-cn-l,2,3-triazole (501) with lead tetraacetate (88CC1608). 

Phenyl-1,2,3-triazolo[4,5-e][ 1,2,3,4]tetrazine (24) has been prepared in 81% yield by lead tetraacetate oxidation of the l-amino-5-phenyltriazolotriazole (67) in CH2C12 solution at 0°C. Reddish flakes of this unstable product were obtained after chromatography at — 30°C <88CC1608, 91JCS(P 1)2045). 

Dickinson and Jacobsen [74AC298 75JCS(P1)975] prepared 1,2,4-triazolo[4,3-6]1.2,4,5-tetrazine 520 by reacting 6-phenyl-3-hydrazino-1,2,4,5-tetrazine (519) with carbon disulfide or by reacting 4-amino-5-hydrazino-l,2,4-triazol-3-thione (522) with benzaldehyde in alkaline medium. The reaction involved the air oxidation of tetrahydrotriazolo-... 

Amino-5-methyltriazole and carbethoxy isothiocyanate, stirred in acetonitrile, gave 3-methyl-5-thioxo-l,2,3-triazolo[l,5-a][l,3,5]triazin-7-pne (104) (25°C, 30 min, 65%) (76JHC589). 5-Phenyltriazole-4-diazonium chloride and phenyl isocyanate, stirred in dichloromethane, provided 3,6-diphenyl-l,2,3-triazolo[5,l-d][l,2,3,5]tetrazine-4-one (105) (25°C, 41%) (79TL4253). Finally, diazotized 4-aminotriazole was coupled to 2-naphthol. The product, refluxed in methanol, was cyclized to naphtho[2,l-e][l,2,3]-triazolo[l,5-h] triazine (106) (2 days, 80%) (74JHC867). 

Japanese chemists, on oxidation of l-amino-5-phenyl-l,2,3-triazolo[4,5-first example of the ring enlargement on oxidation of N-aminotriazoles. Probably, the reason for this involves the known instability of fivemembered hetarynes, which lower the activation energy for the )V-nitrene rearrangement relative to that for the fragmentation. 

In contrast to the condensed thiatriazinedioxide (Chapter 8.26), the synthetic potential and reactivity of these thiatriazine derivatives has not been widely explored. Prolonged refluxing of (4) in acetic acid led to the cleavage of the tetrazine ring leading to nitrile imine intermediate (5). The intermediate (5) readily underwent intramolecular cyclization to 8-amino-1,2,4-triazolo[4,3-a]pyrimidin-7(8//)-ones (6) (Scheme 1) <87JOC2220>. 

Amino-3-hydrazino-5-mercapto-l,2,4-triazine (Purpald ) 402 is a well-established reagent for qualitative and quantitative detection of aldehydes. In the presence of an aldehyde or ketone, Purpald is transformed into a fused tetrahydrotetrazine intermediate 403. However, only with aldehydes, further oxidation of 403 takes place to give a deeply purple colored [l,2,4]triazolo[4,3-. ][l,2,4,5]tetrazine-3-thiol 404 (Scheme 95) <2000ALD28>. 

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