1.2.3- Triazoles, 2-amino-, oxidation

Triazole has been prepared by the oxidation of substituted 1,2,4-triazoles, by the treatment of urazole with phosphorus pentasulfide, by heating equimolar quantities of formyl-hydrazine and formamide, by removal of the amino function of 4-amino-l,2,4-triazole, by oxidation of l,2,4-triazole-3(5)-thiol with hydrogen peroxide, by decarboxylation of 1,2,4-triazole-3(5)-carboxylic acid, by heating hydrazine salts with form-amide,by rapidly distilling hydrazine hydrate mixed with two molar equivalents of formamide, i by heating N,N -diformyl-hydrazine with excess ammonia in an autoclave at 200° for 24 hours, and by the reaction of 1,3,5-triazine and hydrazine monohydrochloride. ... 

Other examples of nucleophilic attack on a furoxan ring leading to ring opening/recyclization are the formation of 1,2,3-triazole 1-oxides 198 from 4-alkylamino-3-nitrofuroxans 197 and alkylamines (Scheme 129). 3-Amino-4-nitrofurazan was observed as by-product (95MC194, 96CHE580, 96KGS675). 

Substitution of the 4-nitro group in 3,4-dinitrofuroxan 1176 by ammonia occurs readily, even at low temperature. Subsequent treatment of the obtained amine, product 1177, with r-butylamine results in formation of 4-amino-2-(/-butyl)-5-nitro-l,2,3-triazole 1-oxide 1178. However, there must be some additional side products in the reaction mixture, as the isolated yield of compound 1178 is only 17%. Upon treatment with trifluoroperacetic acid, the r-butyl group is removed. The obtained triazole system can exist in two tautomeric forms, 1179 and 1180 however, the 1-oxide form 1179 is strongly favored (Scheme 195) <2003CHE608>. 

Diazo ketones are converted by amines into 1,2,3-triazoles and by hydrogen sulfide into 1,2,3-thiadiazoles (371 — 372 Z = NR, S). The intramolecular cyclization of suitable precursors is a most useful method for the preparation of the 1,2,3-triazole ring, including (V-amino- and (V-imino-triazoles and triazole N-oxides. 

Aryl-l-(a-cyanoethyl)-triazene 1-oxides 460 upon treatment at room temperature for 0.5h with catalytic or equimolar amounts of KOH in methanol solution cyclize to give 3-aryl-4-amino-5-methyl-l,2,3-triazole 1-oxides 461. The triazenes are synthesized by reaction of 4-nitroben-zenediazonium tetrafluoroborate with N-cyanomethylhydroxyamine 459 (1992BAU1895) (Scheme 133). 

Few examples of triazole 2-oxides have been reported. However the anomalous nitration of 4-amino-3-(dialkylamino)pyridines (183), while not preparatively useful, provides triazolo[4,5-c]py-ridine 2-oxides (187) <92H(34)i49l>. As shown in Scheme 37 and Table 9 an intermediate 4-nitra-minopyridine (184) undergoes two possible modes of cyclization. The first mode (pathway A) affords the TV-oxides (187), while the second mode (pathway B) affords imidazolo[4,5-c]pyridines (190) and imidazolo[4,5-c]-pyridin-4-ones (191). 

In aryl- or amino-substituted 1,2,4-triazols the nitro group enters the side chain [269-271], An attempt to realize the nitration of 3,5-bisphenylamino-l,2,4-triazole led to opening of the triazole ring. Picrylurea was isolated as the only reaction product [272], The nitration products of 2-methyl-l,2,3-triazole 1-oxide under mild conditions (20°C) are a mixture of 5-nitro (75%) and 4-nitro (23%) derivatives. Under more... 

Nitro-l,2,4-triazole (45%) [451] and l-methyl-4-cyano-5-nitropyrazole (42%) [452] were isolated during the oxidation of corresponding aminoazole derivatives by a solution of hydrogen peroxide in trifluoroacetic acid. One of the amino groups in l-acyl-3,5-diamino-l,2,4-triazole is oxidized by hydrogen peroxide in the presence of sodium tungstate [453] (Scheme 59). 

It should be noted that 3-amino-4-nitrofurazan has been isolated as a side product of 1,2,3-triazole 1-oxide in all cases of this reaction. For example, 2-ethyl-4-ethylamine-5-nitro-l,2,3-triazole 1-oxide with excess ethylamine transforms quantitatively into nitroaminofurazan [565] (Scheme 107). 

The molecule of 4-amino-2-methyl-5-nitro-l,2,3-triazole 1-oxide is nearly planar, except that the hydrogen atoms of the methyl group deviate from the ring plane by 0.505, 0.918, and 0.324 A [175], Coplanarity of the nitro group with the ring plane (1.8°) is caused by intramolecular hydrogen bond O...H...N (the O...N distance is 2.851 A). This fact also explains an elongation of N6-O8 bond (1.233 A) relative to N6-07 (1.225 A). 

H NMR spectroscopy was used for the investigation of 2-(2,4-dinitrophenyl)-4-nitro-l,2,3-triazole [600], 4-amino-3-(4-nitro-l,2,3-triazol-l-yl)furazan [601], 2-aryl(heteryl)-4-acetylamino-5-nitro-l,2,3-triazoles [141, 177, 602-604], nucleophilic substitution in the series of 4,5-dinitro-2-alkyl-l,2,3-triazoles [605] and 4,5-dinitro-2-aryl-l,2,3-triazole-l-oxides [606],... 

Oxidation of heterocyclic amino derivatives yields various reaction products depending on the structure of the amine. 4-Benzylamino-3-methyl-4//-1,2,4-triazole is oxidized with DCT in chloroform to give the azomethine derivative 110 (69ZC325). l-Amino-4,5-diphenyl-l,2,3-triazole under the action of CBT forms diphenylacetylene 2-aminobenzotriazole yields cis, cw-l,4-dicyanobuta-l,3-diene and 1-aminobenzotriazole yields a mixture of chlorobenzene and o-dichlorobenzene. Oxidation of 1-aminobenzotriazole in the presence of tetraphenylcyclopentadienone leads to 1,2,3,4-tetraphenylnaphthalene via benzyne intermediate [68JCS(CC)1305 69JCS(C)1474] (Scheme 101). 

Hydrazones (93) derived from the condensation of various aldehydes and 3-substituted 4-amino-3-sulfonyl[l,2,4]triazoles, on oxidative cyclization, afford the corresponding fully conjugated heterocycles (95) (Table 9 and Equation (23)). 

Stilben-4-yl)naphthotriazoles (2) are prepared by diazotization of 4-amino-stilbene-2-sulfonic acid or 4-amino-2-cyano-4 -chlorostilbene, coupling with an ortho-coupling naphthylamine derivative, and finally, oxidation to the triazole. 

The use of an acidic solution of p-anisaldehyde in ethanol to detect aldehyde functionalities on polystyrene polymer supports has been reported (beads are treated with a freshly made solution of p-anisaldehyde (2.55 mL), ethanol (88 mL), sulfuric acid (9 mL), acetic acid (1 mL) and heated at 110°C for 4 min). The colour of the beads depends on the percentage of CHO content such that at 0% of CHO groups, the beads are colourless, -50% CHO content, the beads appear red and at 98% CHO the beads appear burgundy [Vdzquez and Albericio Tetrahedron Lett 42 6691 200]]. A different approach utilises 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald) as the visualizing agent for CHO groups. Resins containing aldehyde functionalities turn dark brown to purple after a 5 min reaction followed by a 10 minute air oxidation [Coumoyer et al. J Comb Chem 4 120 2002]. 

A combination of the preceding type of synthesis and of cyclization of 4-amino-5-arylazopyrimidine can be seen in the novel procedure of Richter and Taylor. Proceeding from phenylazomalonamide-amidine hydrochloride (180), they actually close both rings in this synthesis. The pyrimidine ring (183) is closed by formamide, the triazole (181) one by oxidative cyclization in the presence of cupric sulfate. Both possible sequences of cyclization were used. The synthetic possibilities of this procedure follow from the combination of the two parts. The synthesis was used for 7-substituted 2-phenyl-l,2,3-triazolo[4,5-d]-pyrimidines (184, 185). An analogous procedure was employed to prepare the 7-amino derivatives (188) from phenylazomalondiamidine (186). 

Other non-traditional preparations of 1,2,3-triazoles have been reported. The rearrangement in dioxane/water of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole into (2-aryl-5-phenyl-27/-l,2,3-triazol-4-yl)ureas was investigated mechanistically in terms of substituents on different pathways <06JOC5616>. A general and efficient method for the preparation of 2,4-diary 1-1,2,3-triazoles 140 from a-hydroxyacetophenones 139 and arylhydrazines is reported <06SC2461>. 5-Alkylamino-] //-], 2,3-triazoles were obtained by base-mediated cleavage of cycloadducts of azides to cyclic ketene acetals <06S1943>. Oxidation of N-... 

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