3-Phenyl-1,2,4,5-tetrazine, oxidative

Only about 20 compounds with the tetrahydro-l,2,3,4-tetrazine structure are known, but two X-ray crystallographic analyses have been reported. The structure of 1,4-dimethyl-l,4,5,6-tetrahydro-l,2,3,4-tetrazine 2-oxide (6) is a twisted boat conformation with non-planar terminal nitrogen atoms, which reflects the repulsion in the four-atom six-electron N—N=N—N system. The bond distances and angles are given in Figure 1 (78HCA1622). A similar study of dimethyl 2-phenyl-2,3,4,4a,5,6,7,8-octahydrobenzo-l,2,3,4-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). 

Treatment of verdazyls (48) with mineral acids resulted in disproportionation to 1,2,3,4-tetrahydro-1,2,4,5-tetrazines (75) and l,6-dihydro-l,2,4,5-tetrazinium salts (76). Here one molecule of the verdazyl is reduced to (75) and the other is oxidized to (76). The mechanism of this reaction has been studied by Polumbrik and his group (72ZOR1925). Heating 3-phenyl-1,2-dihydro-1,2,4,5-tetrazine-6(5/f)-thione (77) in 2N hydrochloric acid led to the isolation of 3-phenyl-l,2,4-triazole-5-thione (78) (77KGS1564). 

Basic hydrolysis of 3-phenyl-l,2,4,5-tetrazine (81) led to the isolation of benzalazine (82) in 80% yield (71KGS708). In most other cases studied the isolated product was an aldehyde acylhydrazone (83), indicating that during the basic hydrolysis one carbon atom of the tetrazine ring is reduced from the acid oxidation level to an aldehyde level (78HC<33)1075, p. 1094). A mechanism for the reaction has been proposed by Libmann and Slack (56JCS2253). Benzalazine (82) was also isolated when 3-azido-6-phenyl-l,2,4,5-tetrazine (84) was hydrolyzed by base (71KGS711). 

There is only one expl vie derivative 1-Nitroso-Phenyl-v-Tatrazine. C8H9N502 mw 207.22 N 33.80% OB to C02 -142.84% yel cryst mp, explds about 120°. Pepn is by nitrosa-tion of 2-phenyl-l, 2-dihydro-v-tetrazine with nitrogen oxides... 

In the first step the formation of 5-phenyl-2-TMS-l, 2,3,4,-tetrazole (374) occurs which can either be hydrolyzed to 5-phenyl-l,2,3,4-tetrazole (375) or pyrolysed to give a N-TMS-benzaldehydehydrazonium compound (376). 376 can furthermore either dimerize to form 3,6-diphenyl-l,2,5-bis(TMS)-2,5-dihydro-l,2,4,5-tetrazine (377) and after subsequent hydrolysis and oxidation 3,6-diphenyl-l,2,4,5-tetrazine (3 79) or on the other hand react with a further equivalent 373 yielding in the last step 3,5-diphenyl-l, 2,4-triazole (381)214 (Scheme 55). 

Oxidation of a solution of 3-alkyl(aryl)-l,2,4,5-tetrazines in liquid ammonia with permanganate proved to be an excellent route for preparing 6-amino-l,2,4,5-tetrazines (Scheme 30) (81JHC123). The covalent a-adduct, i.e., amino-dihydro-1,2,4,5-tetrazine, is intermediate, as proved by NMR spectroscopy. Based on model studies of 3-phenyl-1,6-dihydro-1,2,4,5-tetrazine, this non-isolable amino-dihydro-1,2,4,5-tetrazine has been characterized as having a homotetrazole structure A (Scheme 30) (81JOC3805). 

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-... 

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. 

The examples shown are illustrative of the many easy nucleophilic additions to the polyaza-azines both 3-phenyl-l,2,4,5-tetrazine and 1,3,5-triazine itself add ammonia and simple amines (contrast the requirement for hot sodamide (Chichibabin reaction) for pyridine (8.3.1.2)) and thus amino and alkyamino derivatives can be obtained via oxidative trapping with permanganate. 

Amino-2-phenyl-l, 2,3,5-tetrazin-6(3//)-one (8) has been obtained by first oxidizing 2-phenyl-2H-, 2,3-triazole-4,5-diamine (6) with lead(IV) acetate to get l,3-dicyano-2-phenyltriazene (7) and then by irradiating 7 in methanol with a medium-pressure mercury lamp for 7.5 minutes.5... 

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