Triazole systemic

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>. 

Disubstituted 1,2,3-triazoles are usually minor components in the product mixtures obtained from reactions of triazole with electrophiles (see Section 5.01.5). The few regioselective syntheses of such compounds include a reaction of aminoacetophenones 1235 with hydrazines. The reaction with methylhydrazine proceeds well without any catalysis, but that with phenylhydrazine requires cupric chloride as a catalyst. It is assumed that hydrazone 1236 that forms in the first step is in a tautomeric equilibrium with its azo form 1237. However, it is not clear how bond formation between the nitrogen atoms and oxidation to the triazole system occurs. 4-Aryltriazoles 1238 are obtained in 50-66% yield (Scheme 205) <2003SC3513>. 

In view of the nature of this edition as a whole, the content of this chapter is restricted to describing the chemistry of monocyclic 1,2,4-triazole systems. Readers are directed to the relevant chapters elsewhere in this edition for details of the chemistry of fused heterocyclic systems that contain a 1,2,4-triazole moiety examples of fused systems are only cited in this chapter where relevant. 

This is consistent with the relative values for Dq(Ni2+) (1160 and 1170 cm-1 for 23 and 24, respectively) [36]. For 2-(l,2,4-triazol-3-yl)pyridine 26 Dq(Ni2+) is somewhat smaller,1130 cm-1, and for this and certain substituted derivatives the spin transitions in the [Fe N6]2+ derivatives are observed below room temperature [29]. This and related triazole systems are discussed more fully in chapter 5 by van Koningsbruggen. 

The 1,2,4-triazole system has been found to be particularly suited towards generating spin crossover behaviour in Fe(II)N6 derivatives of the simple molecule and in bidentate and tridentate systems containing at least one... 

Tomas et al. [281] have calculated the tautomeric equilibrium of 1,2,3-benzotriazole in the gas phase and compared their results to experimental data [282] derived from ultraviolet spectroscopy. Experiment suggests that 35 is about 4 kcal/mol more stable than 34 this result is consistent with calculations [281] at the MP2/6-31G level, which predict 35 to be 2.5 kcal/mol more stable than 34. The same level of theory predicts 33 to be 5.0 kcal/mol more stable than 32 in the parent triazole system. Although experimental data are available indicating 35 to be the dominant tautomer in CDCf and d6-dimethyl sulfoxide solutions [279, 283], this equilibrium does not appear to have been the subject of any modeling, continuum or otherwise. It may prove to be somewhat challenging, however. Tomas et al. point out that correlation effects favor 35 by about 5 kcal/mol at the MP2 level AMI, PM3, and HF calculations with moderate basis sets all predict... 

Ring opening of also a fused [l,2,4]triazole system by secondary amines has been reported. Chupakhin et al. described that 5-methyl-6-nitro[l,2,4]triazolo[l,5-r ]pyrimidin-7(8/f)one 122 underwent ring opening when treated with various secondary amines to yield pyrimidyl ureas 123 in medium to good yield <2001IZV655>, as shown in Scheme 14. 

Predictably, 1,2,4-triazole is alkylated preferentially at the 1-position [36, 38,39]. Specific alkylation at the 4-position can be achieved by the initial reaction with dibromomethane to form the bis-triazol-l-ylmethane (see below), followed by quat-emization of the triazole system at the 4-position and subsequent C-N cleavage of the 1,1 -methylenebistriazolium salts [40]. 1,2,3-Benztriazole yields a mixture of the isomeric 1- and 2-alkylated derivatives [41]. The 1-isomer predominates, but the ratio depends on whether the reactions are conducted in the presence, or absence, of a nonpolar organic solvent (Table 5.33). Higher ratios of the 1-isomer are obtained under solidrliquid two-phase conditions. Thus, alkylation of 1,2,3-benztriazole with benzyl chloride produces an overall yield of 95% with the l- 2-isomer ratio of ca. 5.7 1 similar reactions with diphenylmethyl and triphenylmethyl chlorides gives overall yields of 95% (9 1 ratio) and 70% (100% 1-isomer), respectively [38], 6-Substituted purines are alkylated at the N9-atom and reaction with 1-bromo-3-chloropropane yields exclusively the 9-chloropropyl derivative (cf. reaction wi phenols) [42]. 

The energy gained in producing the aromatic triazole system facilitates the retro-Diels-Alder reaction of suitably substituted triazolines. The reaction is potentially useful as a method of synthesis of highly reactive species (e.g.. Scheme 18) rather than as a preparative procedure for triazoles. 

In contrast to the heterocyclic coupling components, virtually all the heterocyclic diazo components that provide commercially important azo dyes contain sulfur, either alone or in combination with nitrogen (the one notable exception is the triazole system). These S or S/N heterocyclic azo dyes provide bright, strong shades that range from red through blue to... 

Two routes to the l//-[l]benzothieno[2,3-comparative study. Reduction of 3-amino-2-nitrobenzothiophene (104) followed by reaction with... 

An interesting development of the reaction of (V-phenylmaleimide with azides is the synthesis of a polymer-bound pyrrolo[3,4-6 ]-l,2,3-triazole system, potentially useful as a linkage in block-and graft-copolymers. First, 2-azido-2,4,4-trimethylpentane was successfully reacted with bis(4-maleimidophenyl)methane to yield the bis-adduct (166). This subsequently led to azide-bearing poly(2-methylpropene) being reacted with bis(4-maleimidophenyl)methane to yield a mixture of mono- and bis-adducts <92MAC2495>. 

The 1,2,3-triazole system can be formally derived from pyrrole or indole by replacing two carbons by two nitrogen atoms. The resulting parent compounds may be classified in terms of the constitutional formulae (l)-(3). In the literature this ring system is still named u-triazole , in order to distinguish it from s-triazole . While (1) and (2) can be considered to depict heteroaromatic systems, (3) is a non-aromatic compound and is rarely found in the literature. In the older literature the term osotriazole belongs to derivatives of (2), particularly if these are derived from osazones. 

Recently propargyl alcohols were reported to undergo FeCb-catalyzed triazole propargylation to yield propargylated triazoles. A mixture of N-2 and N-1 isomers is generally produced. The products of the reaction were then further derivatized via click chemistry to synthesize bis-triazole systems. 

Fused-1,2,3-triazole systems were reported. Parent names and references of the scaffolds are shown below. Intramolecular cycloaddition of an interconverting set of isomeric allylic azides with alkynes afforded stereo-isomeric vinyl-substituted triazoloxazines (140L1844). 

Fused-1,2,3-triazole systems were reported. Parent names and references of the scaffolds are shown below... 

Carpino, L. A. and El-Faham, A. (1999) The diisopropyl/l-hydroxy-7-azabenzo-triazole system segment coupling and stepwise peptide assembly. Tetrahedron 55, 6813-6830. 

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