1.2.4- Triazole - from 3-amino

Ruccia and co-workers187, 188 also succeeded in obtaining some 1,2,4-triazoles from 3-amino-l,2,4-oxadiazoles by the series of reactions shown in Eq. (71). Isolation of the intermediate (99) could also be bypassed by heating 98 directly with the p-toluidine at 120°-170°. 

Examples of the Dimroth rearrangement (Section IV, F) include several s3mtheses of monocyclic triazoles from other heterocyclic systems (cf. Scheme 25). Triazole-5-thiols can be prepared by treatment of 5-amino-l,2,3-thiadiazoles with bases.A similar base-induced rearrangement of sydnoneimines provides a synthesis of 4-hydroxy-triazoles. ... 

Agrawal and co-workers synthesized l,3-bis(l,2,4-triazol-3-amino)-2,4,6-trinitroben-zene (SDATO or BTATNB) (100) from the reaction of two equivalents of 3-amino-1,2,4-triazole (98) with styphnyl chloride (85). The performance of SDATO (calculated VOD 7609 m/s) is slightly higher than PATO while showing more insensitivity to impact. 

The photoinduced -elimination of 1,2,3-triazole from 1-(A,A-bisacyl)amino-l,2,3-triazoles (142), itself formed from the photochemical isomerization of triazoles (141), proceeds either via an intra-or intermolecular hydrogen abstraction or electron-transfer mechanism followed by homolytic cleavage of the A,A-bond (path a) or via t -assisted )8-cleavage of the same weak bond (path b). The composition of the products suggests that in all cases a c-type 1,2,3-triazolyl radical (143) is eliminated which is further quenched by hydrogen abstraction as shown in Scheme 24 <93JHC1301>. 

Fig. 6.3 CycUc voltammogram (1st cycle) of sterling silver (92.5% Ag, 7.5% Cu) in 0.5M NaCH3COO, pH 4, v = lOmV/s copper and silver oxidation peaks, indicating surface passivation in presence of Ata (3-amino,1,2,4-triazole) (from [304])...

Examples include the synthesis of 3-amino-l,2,4-oxadiazoles starting from 3-acylamino-5-methyl-l,2,4-oxadiazole <2002H811> and 2-aryl-l,2,3-triazoles from l,2,4-oxadiazole-3-ketone arylhydrazones <1999T12885, 2006JOC5616>. Oximes, hydrazones, formamidines, and thioureas of the furazan series also undergo base-catalyzed mononuclear rearrangements <2004RCB1121>. Nucleophilic attack at N(3) takes place in the benzofuroxan series. For example, reaction with secondary amines leads to o-nitroarylhydrazines (Scheme 55). 

There are some literature reports on the reactions of 1,2,4-triazoles. 2-Amino-4-aryl-5-( I //-l, 2,4-triazol-1 -yl)thiazolc derivatives were synthesized from the reaction of a-bromo substituted acetophenone and thiourea <07SC199>. 5-Amino-l-methyl-l//-[l,2,4]triazole-3-carboxylic acid were employed as precursors in peptide synthesis <07SC1917>. 3-... 

Meng and Kung [18] also exploited a robust, regioselective synthetic approach to 3-amino-l,2,4-triazoles from commercially available carbonic acid benzyl ester 4-nitrophenyl ester (vi). 

Scheme 2. General scheme for the synthesis of enantiopure fused triazoles from L-amino acids. 2424 www.eurjoc.org 2008 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim...

From amino- and alkoxybutenones and benzonitrile /V-oxide as weU as from acetyl- andethoxycarbonyl-A/-phenylnitrilamines andp-methoxyphenyl azide, the corresponding functional isoxazoles, pyrazoles, and triazoles were obtained (83DIS 83ZOR2281 92SC2902). 

Nitrile molecules from 4-amino-l,2,4- Deamination of N-amino-N-triazoles. 4-Amino-3,5-diphenyl-l,2,4-tri- heterocyclics. N-Aminocarbazole azole... 

Sodium hydroxide 5-Mercapto-l,2,3-triazoles from 5-amino-l,2,3-thiadiazoles... 

Amino-3-sulfonylamino-l, 2,4-triazoles from N -cyano-N-sulfonylisothioureas... 

Triazoles from azides and enamines via 5-amino-J -1,2,3-triazolines... 

Bentiss et al. [97] has synthesized 3,5-disubstituted-4-amino-l,2,4-triazoles from the reaction of aromatic nitriles with NH2NH2.2HCI in the presence of NH2NH2.2H2O excess in ethylene glycol under MW irradiation (Scheme 3.37). 

Amino-3-mercapto-4H-l,2,4-triazoles from 3-aroylditbiocarbazic acids... 

Within the huge field of heterocyclic rearrangements [53], the Dimroth rearrangement gives 5-mercapto-l,2,3-triazoles from 5-amino-l,2,3-thiadiazoles and allows interconversion of 5-amino-l,2,3-triazoles into a mixture of isomers under basic condition [54]. Thus, this reaction, discovered in 1909, involves a linear intermediate that can cyclize into two isomeric compounds (Scheme 15) [55]. This ring-chain tautomerization is reversible, but the equilibrium can be pushed toward an end if one of the two isomers is stabilized. 

An experimental and theoretical investigation of electronic effects in ruthenium catalyzed cycloadditions with internal diarylalkynes has shown that 5-electron-donating group substituted triazoles should be favored [155]. This effect was further observed in the synthesis of 5-amino-triazoles from ynamides (Scheme 65) [156]. 

SCHEME 2.164 Synthesis of di(pyrrol-2-yl)-l,2,4,5-tetrazine or 3,5-di(pyrrol-2-yl) -amino-l,2,4-triazole from pyrrole-2-carbonitrile and hydrazine hydrate. 

Ph3SnNCS OP(licH2CH20CH2CiH2)2NHC2H2N3 (l-amino-l,5 -triazol), from components in ROH, in 83% yield, m. 70-76 (1838a) [SnC29H34lV0 PS]. 

Hydrazine hydrate is known to react with acetonitrile in the presence of sulfur or ethanol to form 4-amino-3,5-dimethyl-l,2,4-triazole or 3,6-disubstitued-l,2-dihydro-l,2,4,5-tetrazines. The initial product, which is disubstituted l,2-dihydro-l,2,4,5-tetrazine, is readily oxidized to the pink colored 1,2,4,5-tetrazine it may also rearrange at elevated temperature or on treatment with an acid to the corresponding 1,2,4-triazole. The triazole compound is obtained by the reaction of hydrazine hydrate and acetonitrile in the presence of CO2. The presence of CO2 in the formation of the six-membered ring intermediate is essential, and has been confirmed by repeating the experiments in the absence of CO2. However, the exact role of CO2 in this reaction is not clear. Figure 6.1 gives a possible mechanism for the formation of the triazole from hydrazinium hydrazine carboxylate and acetonitrile. 

Cyanopyrazole is obtained from treatment of 4-amino-3-halopyridazines with potassium amide in liquid ammonia, while 4-amino-3,6-dihalopyridazines are rearranged under the same conditions to 3-cyanomethyl-l,2,4-triazole. 

The 4- and 5-amino-l,2,3-triazoles are diazotizable, e.g. the diazonium salt from 4-aminotriazole-5-carboxamide with potassium iodide gives the 4-iodo derivative, and that from 4-amino-l,5-diphenyltriazole gives 1,5-diphenyltriazole in ethanol (74AHC(16)33). 

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