Triazole ring reactivity

Protons of 1,2,3-triazole rings can also be activated by A -oxides. The H(4) and H(5) protons in 3-substituted 1,2,3-triazole-1 -oxides (254) are more reactive but exchange with deuterium at a similar... 

The formation of triazole rings by the reactions of azides and acetylenes was first described by Huisgen and coworkers [48,49] and has recently been promoted as dick chemistry by Sharpless et al. [50,51]. This versatile [3 + 2] dipolar cycloaddition proved to be useful for the synthesis of hyperbranched polytriazoles via 1,3-dipolar polycydoaddition of AB2-type monomers 28 and 29 (Scheme 14) [52], The monomers exhibited very high reactivity the... 

Synthesis starting from amidrazones (Scheme 59, c -d") is the most versatile preparation of the 1,2,4-triazole ring. Application to specific cases is governed by three considerations. One is the formation of the required amidrazone from a hydrazine with or without substituents and amide derivatives RC(=NH)X or RC(=NCOR )X where X = halide, OH, OAlk, SAlk, NH2, etc. With two reactive hydrazinic NH groups, isomeric amidrazones can be formed but the relative basicities usually predict the correct product. Unsymmetrical hydrazines YZNNH2 also form amidrazones but these cannot be cyclized unless Y or Z is reactive. 

Molecules containing a fused 1,2,3-triazole ring, as in (8), (11), (12), (26), (27), (33) and (36), frequently display a diazo characteristic in their chemical reactivity that leads to homolytic and heterolytic ring fission. This is a result of an equilibrium that can exist between the closed and open forms (A) and (B) analogous to the ring-chain tautomerism exhibited by fused tetrazoles. Some studies have been undertaken (7UCS(C)2156) to evaluate the role that this equilibrium plays in the physical and chemical properties of fused 1,2,3-triazoles. 

NMR spectra analysis suggested that the triazole byproduct, formed by click side reaction and terminating the polymerization, was not present. The triazole ring underwent a highly selective ring-opening reaction to produce the reactive ketenimine and eventually form polyimidates. 

Azole anions are derived from imidazoles, pyrazoles, triazoles or tetrazoles by proto loss from a ring NH group. In contrast to the neutral azoles, azole anions show enhance reactivity toward electrophiles, both at the nitrogen (Section 4.02.1.3.6) and carbon aton (Section 4.02.1.4.1(i)). They are correspondingly unreactive toward nucleophiles. 

Pyrazolino[2,3-c][l,2,3]triazoles, 5, 702 Pyrazolium hydroxide, l,2-dimethyl-3,5-diphenylanhydro-4-hydroxy-IR spectra, 5, 201 Pyrazolium salts dequatemization, 5, 269 H NMR, 5, 185 hydrogen exchange at ring carbon, 5, 245 mesoionic compounds, 5, 171 nitrodebromination, 5, 237 reactivity, 5, 217 reduction, 5, 68, 243 synthesis, 5, 156 UV spectra, 5, 199 Pyrazolium salts, amino-reactions, 5, 262 Pyrazolium salts, bromo-nucleophilic displacements, 5, 266 Pyrazolium salts, 1,2-dimethyl-deuteration, 5, 175, 245 hydrogen exchange, 5, 71 acid-catalyzed, 5, 239 reactions... 

The compounds referred to as azolides are heterocyclic amides in which the amide nitrogen is part of an azole ring, such as imidazole, pyrazole, triazole, tetrazole, benzimidazole, benzotriazole, and their substituted derivatives. In contrast to normal amides, most of which show particularly low reactivities in such nucleophilic reactions as hydrolysis, alcoholysis, aminolysis, etc., the azolides are characterized by high reactivities in reactions with nucleophiles within the carbonyl group placing these compounds at about the same reactivity level as the corresponding acid chlorides or anhydrides. 11... 

Scheme 33 illustrates the difference in reactivity between triazolines obtained from cyclohexanone and cyclo-pentanone enamines. Thus, the reactions of azidophosphonates 239 with cyclohexanone enamines produce unstable aminotriazolines 240 that cannot be isolated due to their spontaneous elimination of amines to provide triazoles 241. Contrary to that, triazolines 242, derived from cyclopentanone enamines, are isolated in good yield (76-88%) and cannot be converted to the corresponding triazoles even by thermolysis <1995H(40)543>. Probably, introduction of a double bond between two five-membered rings would involve too much molecular strain. 

All procedures for ring closure to the title ring system by cyclization of the six-membered ring utilize the reactivity of 3,4-diamino[l,2,4]triazoles 209 these compounds can easily react with bifunctional reagents bearing these functional groups in adjacent positions. 

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