5-Aminotetrazole reactions

Substituted 5-aminotetrazoles Reactions with electrophiles and oxidation... 

In a rather different reaction, aminotetrazoles treated with bromine lose nitrogen and give isocyanide dibromides (77AHC(2l)323) probably the mechanism is as shown in Scheme 54. 

Attempted diazotization in dilute acid sometimes yields primary nitroso compounds. Reactions of 3- and 5-amino-1,2,4-thiadiazoles with sodium nitrite and acid give primary nitrosamines (e.g. 432->433) (65AHC(5)n9) which can be related to the secondary nitrosamines (434) prepared in the normal way. 1-Substituted 5-aminotetrazoles with nitrous acid give stable primary nitrosamines (435). Primary nitrosamines have been isolated in the imidazole series. 

The high reactivity of heterocyclic diazonium ions in azo coupling reactions is the reason why in some cases the primary diazotization products cannot be isolated. For example, diazotization of 2-methyl-5-aminotetrazole (2.14) directly yields the triazene 2.15, i. e., the N-coupling product, since the intermediate diazonium ion is reactive enough to give the N-coupling product with the parent amine even under strongly acidic conditions (Scheme 2-8 Butler and Scott, 1967). 

Diazotised 5-aminotetrazole is unstable under the conditions recommended for its use as a biochemical reagent. While the pH of the diazotised material (the cation of which contains 87% nitrogen) at 0°C was being reduced to 5 by addition of potassium hydroxide, a violent explosion occurred [1], This may have been caused by a local excess of alkali causing the formation of the internal salt, 5-diazoniotetrazolide, which will explode in concentrated solution at 0°C [2], The diazonium chloride is also very unstable in concentrated solution at 0°C. Small-scale diazotisation (2 g of amine) and susequent coupling at pH 3 with ethyl cyanoacetate to prepare ethyl 2-cyano-(l//-tetrazol-5-ylhydrazono)acetate proceeded uneventfully, but on double the scale a violent explosion occurred [3], The importance of adequate dilution of the reaction media to prevent explosions during diazotisation is stressed [4]. 

The reaction of 73 with 2-aminotetrazole hydrate gave different products depending on the reaction conditions. Under the conditions applied for the preparation of 74 4-oxo-3-phenylpyrido[2,1 -/] [ 1,2,4]triazinium-2-olate 75 was obtained, whereas the amino derivative 76 was obtained by using diisopropylethylamine (Hunig s base) as the base (Scheme 1) <1996T11349>. 

Other approaches to tetrazoles were also recently published. Primary and secondary amines 195 were reacted with isothiocyanates to afford thioureas 196, which underwent mercury(II)-promoted attack of azide anion, to provide 5-aminotetrazoles 197 . A modified Ugi reaction of substituted methylisocyanoacetates 198, ketones, primary amines, and trimethylsilyldiazomethane afforded the one-pot solution phase preparation of fused tetrazole-ketopiperazines 200 via intermediate 199 <00TL8729>. Microwave-assisted preparation of aryl cyanides, prepared from aryl bromides 201, with sodium azide afforded aryl tetrazoles 202 . 

The synthesis of the polycyclic 5-5-6-5 derivative 81 was realized by nucleophilic substitution of the 5,6-dichloro[ 1,2,5]oxadiazolo[5,4-7]pyrazine 79 with 5-aminotetrazole 80 (Scheme 17). This conversion took place at room temperature and the product 81 was isolated in moderate 36% yield. Many other heterocyclizations with N,N, N,0-, /V,.Y-bidentate nucleophiles gave the corresponding reaction in up to 93% yield <1997CHE1352>. 

In Scheme 20, another ring closure starting from 5-aminotetrazole is shown, which should be discussed in more detail. Nenajdenko and co-workers carried out studies on ring closure reactions taking place between 1,1,1-trifluoro-4-sulfonyl-but-3-ene-2,2-diols 107 and a series of aminoazoles <2002S901>. They found that the reaction can take place in two different ways and, thus, the isomers 108 and 109 can be formed. Reaction of 107 with 5-aminotetrazole 106 was found to proceed regioselectively, and yielded the 5-trifluoromethyl compound 108 as the main product in good yield (72%). The other isomer 109 was found only in traces. 

The reaction sequence starts from tetrazolyldiazonium salt 42 prepared from aminotetrazole 41 by diazotation. This compound when reacted with arylformylacetonitrile 43 leads to the intermediate formation of the condensation product 44, which easily undergoes ring closure to 45. This tetrazolo[5,l-z][l,2,4]triazine compound, however, forms an equilibrium with the valence bond isomeric azide 46, which can participate in a different ring closure than the reverse route, and yields the tetrazolo[l,5-A][l,2,4]triazine product 47. The reaction was carried out with a series of various aryl derivatives and proceeded in good to excellent yields (68-87%). 

Formation of the partially saturated nitro derivatives 60 and 61 was reported by a Russian team <1994KGS1129>. The two products were obtained under fairly complicated reaction conditions when aminotetrazole 42 was first treated with potassium amidosulfonate and formaldehyde at pH = 4 followed by addition of nitric acid, methylamine, and acetic anhydride, product 60 was obtained in 24% yield. The same reaction, however, carried out at pH = 6 gave rise to formation of the acetoxy compound 61 in 21% yield. 

Scheme 29). The reaction of 5-aminotetrazole with diphenylacetylene may similarly involve the intermediacy of hydrazoic acid. ... 

The high nitrogen content and the endothermic nature of the tetrazole ring lends itself to the synthesis of energetic materials. Compounds such as -H tetrazole and 5-aminotetrazole can be used as nucleophiles to incorporate the tetrazole ring into other molecules. 5-Aminotetrazole is synthesized from the reaction of dicyandiamide with sodium azide in hydrochloric acid. 

The reaction of 5-aminotetrazole with 3,5-diamino-2,4,6-trinitrofluorobenzene generates the energetic tetrazole (151). ... 

The reaction of aminoguanidine bicarbonate (84) with sodium nitrite in the presence of excess acetic acid produces 1,3-ditetrazolyltriazine (89), another nitrogen-rich heterocycle (C2H3N11 = 85 % N) which readily forms explosive metal salts. The reaction of aminoguanidine bicarbonate (84) with sodium nitrite in the presence of mineral acid yields guanyl azide (90), of which, the perchlorate and picrate salts are primary explosives. Guanyl azide (90) reacts with sodium hydroxide to form sodium azide, whereas reaction with weak base or acid forms 5-aminotetrazole. ... 

When R2 substituent is flourocontaining alkyl group, the transformation 17 18 becomes hindered and its proceeding requires some special methods. For example, in [48] Biginelli-like cyclocondensations based on three-component treatment of 3-amino-l,2,4-triazole or 5-aminotetrazole with aldehydes and fluorinated 1,3-dicarbonyl compounds were investigated. It was shown that the reaction can directly lead to dihydroazolopyrimidines 20, but in the most cases intermediate tetrahydroderivatives 19 were obtained (Scheme 10). To carry out dehydration reaction, refluxing of tetrahydroderivatives 19 in toluene in the presence of p-TSA with removal of the liberated water by azeotropic distillation was used. The same situation was observed for the linear reaction proceeding via the formation of unsaturated esters 21. 

Scheme 18) [72]. It is interesting to note that this MCR involving 5-aminotetrazole was unsuccessful and only the starting materials were reisolated from the reaction mixture. An explanation for this unreactivity could be the decrease in nucleophilicity comparing 3-amino-l,2,4-triazole and 2-aminobenzimidazole with 5-aminotetrazole. The same observations regarding the reactivity characteristics for these aminoazoles have already been reported before [73]. 

The imidoyl azide-tetrazole ring-chain isomerism of tetrazoles develops into a wide-ranging example of the Dimroth rearrangement in the thermal behavior of substituted 5-aminotetrazoles <84JHC627>. An example with 5-hydrazinotetrazoles is shown in Scheme 10 <88BSB543>. The reaction... 

Mercuric-5-nitrotetrazole [Structure (2.13)] was prepared according to the methods reported by Gilligan et al. [14] and Redman and Spear [15]. Thus, 5-aminotetrazole was treated with sodium nitrite and copper sulfate to obtain Cu(NT)2HNT-4H20 (where NT nitrotetrazole). The copper salt was subsequently converted to the ethylene diamine complex MNT was then obtained by treating the complex with mercuric nitrate in HN03 medium. The precursors and final product were air dried. The synthesis of these compounds is carried out in a fume hood behind a protective polycarbonate shield in a stainless steel reaction vessel. 

The reaction of aminoguanidine with nitrous acid in the presence of an excess of acetic acid gives also l,3-ditetrazyltriazine(IX).It is possible that 5-aminotetrazole first arises, which then undergoes diazotization and the diazo compound thus formed couples with the remaining aminotetrazole ... 

Some systems have been obtained by a modification of the above procedure in which propargyl bromide replaces the cr-halogenoketone. Table II summarizes the systems that have been prepared by the Tschitschibabin reaction, together with the preparative route used. However, certain difficulties are encountered with this method. The syntheses of imidazo[l,2-6]-s-triazoles and imidazo[l,2-d]tetrazoles have been reported,20813 but repetition of this work more recently209 has cast doubt on these results. 5-Aminotetrazole was found to react with arylacyl bromides to give products shown to be AT-substituted tetrazoles 203 and not imidazol 1,2-rf]tetrazoles (204) as previously suggested.20813... 

Treatment of ethyl l-oxo-l//-pyrimido[l,2-a]quinoline-2-carboxylates with ammonia in methanol and hydrazine hydrate in ethanol at ambient temperature afforded 2-carboxamides and 2-carbohydrazides, respectively (74MIP1 79MIP2). Reaction of l-oxo-l//-pyrimido[l,2,-a]quinoline-2-carboxylic acids (169) with A-. /V-carbonyldiimidazole in dimethyl-formamide, then with 5-aminotetrazole gave 7V-(5-tetrazolyl)-1 -oxo-1H-pyrimido[l,2-a]quinoline-2-carboxamides (170) (77GEP2630469 77USP 4017625). 

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