2//-l,23-Triazole

Pyrazolo[l,2- ][l,2,3]triazole mesomeric betaines are generally available by an electrophilic attack of singlet nitrenes on the pyrazole nitrogen atom. When phthalazone derivative 252 is used and the nitrene is generated by reduction with triethyl phosphite, 59% yield of mesomeric betaine 253 is obtained (Equation 40) <2000T5523>. 

In the presence of copper and palladium catalysts, terminal alkynes 1222 react with trimethylsilyl azide and allyl methyl carbonate to provide 2,4-disubstituted 1,2,3-triazoles 1223 in moderate to good yield. Isomerization of the allyl substituent in the presence of a ruthenium catalyst gives 4-substituted 2-(l-propen-l-yl)-2//-l,2,3-triazoles 1224. 

Arylazo-4-(3-ethoxycarbonylureido)furoxans 62, which were synthesized by the reactions of 4-amino-3-arylazo-furoxans with ethoxycarbonyl isocyanate, were subjected to cascade rearrangements under the action of potassium r/-butoxidc in dimethylformamide or by heating in dimethyl sulfoxide to form 4-amino-2-aryl-5-nitro-2//-l,2,3-triazoles 63 (Scheme 13) <2001MC230, 2003RCB1829>. 

Calculations at the 6-3IG level indicate that in the gas phase, 2//-l,2,3-triazole is more stable than 1//-1,2,3-triazole by about 4.5 kcal moC. In solution, the IH isomer becomes the more stable species because the large difference in dipole moments favors the more polar tautomer. The triazolium ion (75) is predicted to be more stable than (76) by about 13.5 kcal mol <89Mi40i-0i>. 2//-1,2,3-Triazole represents more than 99.9% of the equilibrium mixture in the gas phase. However, the ab initio calculated proton affinity of 1//-benzotriazole is 10.2 kcal mol larger than that of 2//-benzotriazole, which is consistent with ICR measurements (1-methylbenzotriazole is 10 kcal mol more basic than 2-methylbenzotriazole). Measurements of enthalpies of solution, vaporization, sublimation and solvation in water, methanol and DMSO confirm the predominance of the IH tautomer in solution <89JA7348>. The energy difference between the tautomers of 1,2,3-triazole has also been estimated at the 6-31G (MP2)//3-21G level including zero-point effects. The... 

Oxidation of 3,5-diamino-4-arylhydrazonopyrazoles (802) with lead tetraacetate gives 2-aryl-4-cyano-2//-l,2,3-triazoles (803) in moderate yield (Equation (75)). A mechanism involving pyr-azolotriazole and/or nitrene intermediates is proposed <86JCS(P1)1379>. 

Reaction of p-tolyl substituted 2H-1,2,3-triazoles with anils of aromatic aldehydes was originally confined to the 2-(p-tolyl)-4-phenyl-and 2-(/)-tolyl)-4,5-diphenyl-2//-l,2,3-triazoles (134a and b), which, with 4-phenylbenzalaniIine, gave the styryl derivatives 135a and b, respectively.57... 

Furthermore, with Schiff s base 72 from 4,4 -diformylbiphenyl and p-chloroaniline, 134byields the4,4 -bis[4-(4,5-diphenyl-2//-l,2,3-triazol-2-yl)styryl]biphenyl (136).43... 

Di-(p-tolyl)-5-methyl-2//-l,2,3-triazole (137) was found to react with 2 moles of benzalaniline to give the distilbenyltriazole 138, where-... 

As part of their study on aza-transfer reactions, Tisler and co-work-ers289 290 reacted 2-hydrazino-4-oxo-4//-pyrido[l,2-u]pyrimidine with various diazo derivatives and obtained 2-azido- and 2-amino-4-oxo-4/f-pyrido[l,2-u]pyrimidines. From 2-azido-4-oxo-4/f-pyrido[l,2-u]pyrimi-dines various derivatives of 2-(l,2,3-triazol-l-yl)-4-oxo-4//-pyrido[1.2- ]-pyrimidine (221) were prepared by reaction with acetylene,287 1,3-dioxo compounds,166 ordiethylamine.291 For further ring transformation reactions of the 2-azido-4-oxo-4//-pyrido[l,2- ]pyrimidine (102), see Section lll.C.lO. 

A thermally induced rearrangement of arylhydrazones of furoxan-3-carbonyl compounds into 2-aryl-5-[(hydroximino)arylmethyl]-2//-l,2,3-triazole 1-oxides has been observed for the first time.156 2-(2,2-Dicyano-l-hydroxyethenyl)-l-methylpyrroles (192) are readily rearranged to their 3-isomers (193) in nearly quantitative yield when heated to 75-142 °C. The inter- or intra-molecular auto-protonation of a pyrrole ring... 

Tsai CW, Yang SC, Liu YM et al (2009) Microwave-assisted cycloadditions of 2-alkynylbenzonitriles with sodium azide selective synthesis of tetrazolo[5,l-a]pyridines and 4,5-disubstituted-2//-l,2,3-triazoles. Tetrahedron 65 8367-8372... 

Triazoles can be acylated in the usual manner, e.g. with acyl halides and anhydrides. Isocyanates react with the formation of mixed ureas (139), which show characteristic short-wave carbonyl absorptions (1745, 1788 cm ) (61LA(648)72). Treatment of 1,2,3-triazole with thiobenzoyl chloride in the presence of triethylamine yields a mixture of 1-thiobenzoyl-lH- and 2-thiobenzoyl-2//-l,2,3-triazoles (73LA636). 

JCS(P2)i9). In a similar manner, 4,4-diazido-2-pyrazolin-5-ones (343) are converted into 2//-l,2,3-triazole-4-carboxylic acids (344) (8ozc437). 

The conversion of the (Z)-phenylhydrazone of 5-amino-3-benzoyl-l,2,4-oxadiazole into the relevant 1,2,3-triazole in the presence of several haloacetic acids and the kinetics of the rearrangement of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole to (2-aryl-5-phenyl-2//-l,2,3-triazol-4-yl)ureas have been reported. Treatment of benzannulated enediynyl alcohols with trifluoroacetic acid promoted a cascade sequence of cyclization reactions leading to 1,4-naphthoquinone methides (Scheme 37)7 ... 

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