4-Aryl-l,2,3-triazoles

UV irradiation of 2-arylbenzotriazoles (144), including the commercially available photostabilizer Tinuvin P, in an aerated solvent results in oxidation of the benzo ring to give the 2-aryl-l,2,3-triazole-4,5-dicarboxylic acid (146), possibly via the intermediate 2-arylbenzotriazole-4,7-dione (145) (Scheme 25). Indeed, when the independently synthesized l-phenyl-2. -benzotriazole-4,7-dione (145, R = = H) is irradiated under the same conditions, compound (146 R = R = H) is formed, and... 

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). 

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],... 

Regiospecific synthesis of 2-substituted-l,2,3-triazoles are rare. 5-Carbomethoxy-2-carbomethoxymethyl-4-trinitromethyl-l,2,3-triazole (84a) was prepared by 1,3-dipolar cycloaddition/ alkylation of NCC(N02)3 with Me02CCHN2. X-ray crystallographic data shows the trinitromethyl substituent of 83a is a strained sp center which infers chemical reactivity comparable to that observed for polynitrometnanes thus, 84a with ethanolic KOH afforded potassium 4-dinitromethyl-l,2,3-triazole salt (84b) [93ZOR(29)1231]. Copper-catalyzed oxidative cyclizations of arylhydrazones, while sensitive to substituent effects, provides 2-aryl-l,2,3-triazoles (85) [94H(38)739]. 

Pyridine N-oxides undergo palladium-catalyzed direct C-H coupling with 2-aryl-l, 2,3-triazole N-oxides (Scheme 35) (130L4682). The reaction occurs regioselectively. In addition to tolerating substituents on the pyridine N-oxide, the aryl group of the 1,2,3-triazole can also have a range... 

The palladium-catalysed arylation of 2-aryl-l,2,3-triazole-A(-oxides by phenyl iodides or boronic acids occurs selectively at the 4-position. The mechanism is likely to involve oxidative addition of the arylating agent to palladium, followed by palladation of... 

The synthesis of 2-aryl-l,2,3-triazoles of type 37, which are used as optical brighteners, is the subject of numerous patents [454]. 

Scheme 203 provides a methodology for the conversion of aryl bromides onto 4-aryl-l,2,3-triazoles. In the given example, palladium-copper catalyzed substitution of the bromine atom in indole 1226 by trimethylsilylacetylene provides intermediate 1227. Hydrolysis of the trimethylsilyl protecting group releases terminal alkyne 1228, isolated... 

Substituent effects on the polarographic reduction of l-amino-4-aryl-l,2,3-triazoles and l//-4-aryl-l,2,3-triazoles of the general formula (67) have been reported. Cathodic halfwave potentials E1/2) determined in acetonitrile at 20 °C were between -2.1 and -2.6 V. Linear relations were found between E1/2 and the tt-electron density at C-5, as well as Hammett [Pg.689]

Ring enlargement of aryl(l,2,3-triazol-l-yl) carbenes, generated from 1-[A -(phenylsulfonyl)benzohydrazonoyl-1,2,3-triazoles 8, into 3-aryl-l,2,4-triazines 9 has been described <05H279>. 

The semilocalized biradicals (39) and (40) have been produced by irradiation of the azo-compound (41) and directly identified by e.s.r. spectroscopy (Ham et al.). Photoelimination of N2 from 1-aryl-l,2,3-triazoles has provided a useful route to indole derivatives (Nagawa et al.). Tsuda and Oikawa have proposed a new mechanism for the photo-Wolff rearrangement. 

Arylthiazoles are found to undergo arylation at C-5. Cleaner and faster reactions are performed in water than in other common solvents." Arylation of 4-aryl-l,2,3-triazoles has also been reported. ... 

Isolated 2,6-bis(l-aryl-l,2,3-triazol-4-yl)pyridines undergo a change in conformation from anti, anti to syn, syn on complexation of the metal cations or protons. Therefore, the response of clickamer 88 to HCl was investigated by CD (circnlar dichroism) spectroscopy in CH3CN water... 

L. Wang, C. Cai, Reusable polymer-supported copper catalyst for one-pot synthesis of 1-aUtyl- and l-aryl-l,2,3-triazoles green, simple, and effective. Green Chem. Lett. Rev. 3 (2010) 121-125. 

In coordination chemistry, architectures containing the triazole heterocycle have been developed as monodentate and polydentate nitrogen ligands. Special attention has been given to (2-pyridyl)- and more flexible (2-picolyl)-l,2,3-triazoles. Thus, a hbrary of selected 1,4-disubstituted 1,2,3-triazoles differently functionahzed with pyridine, pyrimidine, and pyrazine have been synthesized by the reaction of aryl, heteroaryl, and heteroarylmethyl azides with alkynes. Three different copper(l) sources, that is, CuSO /sodium ascorbate, CuBrlPPhglg, and (CuOTf)2 CgHg, were used to promote the reactions [89]. 

Diacetylenic lotsitch reagents with azides (THF, 15-18°C, 20 h) afford l-alkyl(aryl)-5-ethynyl-l,2,3-triazoles (94) in 48-70% yield(67ZOR2241). These... 

Base-catalyzed cyclization of semicarbazide 189 gave the triazolidine 3,5-dione 190, subsequent treatment of which with phosphorus oxychloride gave 3,5-dichloro-4-aryl-l,2,4-triazole 191 (Scheme 17). <2006T2677>. 

Michael-type addition of cyclic amines (piperidine, A-methylpiperazine) to thiazolo[3,2-A][l,2,4]triazole-5(6//)-ones 46 provides an easy entry to 2-aryl(alkyl)-6-(a-aminoarylmethyl)thiazolo[3,2- ][l,2,4]triazol-6(5//)-ones 207 (Equation 19) <1999AF1006, 2001AF470>. 

Very early in the history of heteroeyelic chemistry it was diseovered by Dimroth (09LA183) that l-aryl-5-amino-l,2,3-triazole (1, R = H) undergoes a faeile, reversible isomerization to 5-(arylamino)-l,2,3-triazole (2, R = H) (Scheme IV.4). 

Similarly to the rearrangement observed with l-aryl-5-hydrazino-l, 2,3-triazole (see Section IV,B,l,a), 3-phenyl-2-hydrazonothiazoline (20) is rearranged by acid at room temperature into 3-amino-2-(phenylimino) thiazoline (21) (Scheme IV.12) (61LA66). 

Coumarinyl-substituted thiazolo[3,2-h][l,2,4]triazoles have also been reported. They are available in one step by reaction of 5-aryl-3-mercapto[l,2, 4]triazoles with 3-bromoacetylcoumarin (ethanol, reflux, 8 h yield 44-65%) (81AP435) or in a two-step reaction from the corresponding S-alkylated intermediates with PPA [93MI2 94IJC(B)579]. 2-Aminothiazolo[3,2-h][l,2,4]triazoles are also available from 3-mercaptotriazoles. Treatment of 5-amino-3-mercaptotriazole with chloroacetone (DMF, K2CO3) and subsequent acid-catalyzed cyclization yields 146 [90JAP(K)02/142797]. 

The 5-unsubstituted-l,2,3-triazol-4-ones (176, R = H) participate in electrophilic substitution reactions. Bromination in chloroform of anhydro-4-hydroxy-l,3-dimethyl-1,2,3-triazolium hydroxide (180) gave its 5-bromo derivative (182). The meso-ionic 3-aryl-1,2,3-triazol-4-ones (176, R = Me, R = Ar, R = H) gave 5-bromo derivatives (176, R = Me, R = Ar, R = Br) with bromine in acetic acid. Their reaction with sulphur monochloride gave the sulfide (189, X = S), and with thionyl chloride they gave the sulfoxide (189, X = SO). ... 

Information concerning the chemistry of meso-ionic 3-alkyl- and 3-aryl-l,2,3,4-oxatriazol-5-ones (271) is limited, but further investigation may well be encouraged by reports of pronounced hypotensive activity. 3-Cyclohexyl-1,2,3,4-oxatriazol-5-one (271, R = cyclohexyl) is resistant to attack by dilute mineral acid, but warm concentrated sulfuric acid gives cyclohexanol and carbon dioxide. In contrast, acid hydrolysis of 3-phenyl-l,2,3,4-oxatriazol-5-one (271, R = Ph) yields phenyl azide. Meso-ionic 3-cyclohexyl-l,2,3,4-oxatriazol-5-one shows two unusual reactions its photoirradiation in benzene gives cyclohexanone and heating with diphenylacetylene )delds l-cyclohexyl-4,5-diphenyl-1,2,3-triazole (276) rather than the expected 2-cyclohexyl-4,5-diphenyl-1,2,3-triazole. 

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