3- Phenyl-l,2,3-triazole 1-oxide

Bromine and iodine at the 5-position of 2-phenyl-l,2,3-triazole 1-oxides 361 and 370 could be replaced with lithium or magnesium using BuLi or z -PrMgCl (2010UP2) (Scheme 111). 

Substituents present in the starting material affected product composition according to a series of perceptions extracted from the outcome of the reaction of selected 2-phenyl-l,2,3-triazole 1-oxides with AcCl as illustrated in Scheme 120 (1981JCS(P1)503,1997BSB717). The reasoning is based upon initial formation of an O-acetylated species shown in the left column, which then reacts with acetate ion in the product-determining step. The O-acylated species may react in a similar fashion with other nucleophiles like the chloride ion. 

In C5 unsubstituted 2-methyl or 2-phenyl-l,2,3-triazole 1-oxides the intermediates 400 and 403 react at C5. A methyl group at C4 does not significantly influence product composition. The chloro analogue 380 is formed in minor amounts and is easy to remove. The reaction gives access to substituted acetoxy-l,2,3-triazoles 405 and 406. 

Methyl- and 2-phenyl-triazole 1-oxide (207) are silylated selectively at the 5-position with trimethylsilyl triflate to afford stable 5-trimethylsilyl derivatives (208) (Scheme 35). If the 5-position is blocked with a substituent, the 4-position is silylated. Thus, 5-chlorotriazole 1-oxide is converted to 5-chloro-4-trimethylsilyl-l,2,3-triazole 1-oxide in the presence of lithium tetramethylpiperidine. 

Hydrolysis of 2-phenyl-[l. 2.3]triazolo[4,5-d]pyrimidine-5,7-dione N-oxides 463 in basic solution gives rise to 4-amino- and 4-ureido-2-phenyl-l,2,3-triazole-5-carboxylic acid 1-oxides 464, as well as their hydrazides and methylamide (2005JGU636) (Scheme 134). 

Strongly activating substituents assist halogenation at the adjacent ring site. When 4-hydroxy-2-phenyl-1,2,3-triazole was treated with bromine, the product was mainly 5-bromo, but a small amount of 2-p-bromophenyl product was also observed. The corresponding l-oxide gave only resins when similarly treated (88JOU599). 

Oxidation of chalcone phenylhydrazone 13 leads to a pyrazole and the expelled proton catalyses formation of a pyrazoline from the chalcone phenyl-hydrazone [43]. The latter undergoes further anodic oxidation (p. 308). In the presence of pyridine as a proton acceptor, the pyrazole becomes the major product. A further example of oxidative cyclization is the conversion of a-oximino phenylhydrazones to 1,2,3-triazole-l-oxides 14 [44]. 

Acid hydrolysis of 3-methyl-6-phenyl-l,2,4-triazine 4-oxide (827) yields 4-phenyl-1,2,3-triazole through an acyclic intermediate (828) (Scheme 168) <89AHC(46)73>. 1,2,4-Triazine 2-oxides (829) undergo rearrangement in basic conditions (Equation (80)) to form 4-substituted 2//-1,2,3-triazoles <89AHC(46)73>. l-(2-Nitrophenyl)-5-aryltetrazoles (830) and l-aryl-5-(2-nitrophenyl)tetrazoles are converted into 2-arylbenzotriazoles (831) by refluxing in nitrobenzene (Equation (81)) <81AJC69l>. 

Direct oxidative thiation (Scheme 41) by heating sulfur with triazoles requires a substituent on nuclear nitrogen. The preparation of the thione (123) from 4-phenyl-l,2,4-triazole <66Mi4i20i) is unambiguous, but 1-benzyltriazole affords the 5-thione (124) instead of the 3-isomer that would have been expected on steric grounds (70JCS(C>2403). 

Thionyl chloride added dropwise with stirring at 5° to a suspension of N -phenyl-N -benzoylbenzamidrazone in dimethylformamide containing triethylamine, and stirring continued 15 hrs. at room temp. 4,5-diphenyl-2-benzoyl-l,2,3,5-thia-triazole S-oxide. Y 58%. Also 1,2,4-triazole ring s. H. Reimlinger, W. R. F. Lingier, and J. J. M. Vandewalle, B. 104, 639 (1971). 

Since both oxepin and its valence isomer benzene oxide contain a x-tb-diene structure they are prone to Diels-Alder addition reactions. The dienophiles 4-phenyl- and 4-methyl-4//-l,2,4-triazole-3,5-dione react with substituted oxepins at room temperature to give the 1 1 adducts 7 formed by addition to the diene structure of the respective benzene oxide.149 190,222... 

Reduction of the 1//-1,2-benzodiazepines 6 with lithium aluminum hydride results in the dihydro compounds 8, which are dehydrogenated to the 3H-1,2-benzodiazepines 9 by 4-phenyl-4//-l,2,4-triazole-3,5-dione.123 The products readily revert to the 1//-tautomers in the presence of sodium methoxide. 3//-1,2-Benzodiazepines react with 3-chloroperoxybenzoic acid to give mixtures of 1- and 2-oxides, 10 and 11, in which the latter predominate. Treatment of the 2-oxides 11 with nucleophiles provides 3-substituted H- 1.2-benzodiazepines 12. Selected examples are given.124... 

Other non-traditional preparations of 1,2,3-triazoles have been reported. The rearrangement in dioxane/water of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole into (2-aryl-5-phenyl-27/-l,2,3-triazol-4-yl)ureas was investigated mechanistically in terms of substituents on different pathways <06JOC5616>. A general and efficient method for the preparation of 2,4-diary 1-1,2,3-triazoles 140 from a-hydroxyacetophenones 139 and arylhydrazines is reported <06SC2461>. 5-Alkylamino-] //-], 2,3-triazoles were obtained by base-mediated cleavage of cycloadducts of azides to cyclic ketene acetals <06S1943>. Oxidation of N-... 

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