5- -3-phenyl-177-1,2,4-triazoles

Another problem with this method of synthesis is that unsymmetrical acetylenes can, and usually do, give two isomeric triazoles (Scheme 2). The sterically less hindered isomer is by no means always the major product In addition to phenylacetylene, for example, the 5-phenyl-triazole often predominates in the product mixture. 

Closure to the triazoline certainly occurs in many systems, since products are isolated which can only have been formed by this route. Occasionally these products include w-triazoles for example, 4-phenyl-triazole is isolated in moderate yield from the reaction of the aldehydes (3) with toluene-p-sulfonyl azide (Scheme 9). ... 

Oxidation of 5-anilino-4-phenyl- -triazole may give a 4 -triazolone derivative as an intermediate (Scheme 39). ... 

The NH stretching band in triazole appears in the vapor phase at 3522 cm and in carbon tetrachloride at 3470 cm in the solid phase the NH absorption is a broad band at 2400-3300 cm (for 4-phenyl-triazole). The CH stretching frequency of 4- or 5-unsubstituted triazoles is at 3100-3140 cm (liquid phase).In-plane and out-of-plane deformation bands of the CH bond have also been distinguished at 1237 and 1076 cm (in the solution spectrum of 1,2,3-triazole), at 1290-1150 and 850-700 cm (for various substituted triazoles) and at 1149—1074 and 855-825 cm (for 2-aryltriazoles). ... 

Reaction of 4-aminotriazole-5-carboxamide and 4-amino-5-phenyl-triazole with acetylacetone and piperidine gives a different type of fused triazole, the t>-triazolo[3,4-a]p5Timidine system (Scheme 48). 

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. 

HC=C(N02)-C = N [C6H3(N02)2] It yel crysts(from AcOH), mp 195-6° sol in AcOH, benz or toluene diffc sol in chlf, eth or ale insol in w. Can be prepd by heating 4,6-dinitrobenzo-2-phenyl-triazole with coned nitric-sulfuric acid. Its expl props were not investigated... 

Two alternative routes lead to 2-alkyltriazole 1-oxides from -dicarbonyl compounds (Scheme 244, routes A and B). Unsymmetrical dicarbonyl compounds frequently, but not invariably, give rise to two isomeric hydrazones and two isomeric oximes and hence two isomeric 1,2,3-triazole 1-oxides < 1981 J(P 1 )503>. 2-Phenyl triazole 1-oxide is obtained from glyoxal via route A. However, 2-methyl triazole 1-oxide is prepared from glyoxal by route B in a one-pot process under neutral conditions. 2-Benzyltriazole 1-oxide is obtained similarly. 2,5-Dimethyltriazole 1-oxides are accessible through both routes <1986ACB262>. For reviews on N-substituted 1,2,3-triazoles see <1992AHC(53)85, 1994H(37)1951>. 

In 2008, Ackermann and co-workers demonstrated that the addition of 30 mol% of a carboxylic acid MesC02H tremendously improved the catalytic system [RuCl2(p-cymene)]2/K2C03 for the selective aiylatiOTi of phenyl triazoles with arylbromides in toluene at 120°C. This catalytic system was shown to be efficient even for arylation with arylchlorides of aiyl-oxazoUnes, pyrazoles and alkenes. The catalytic efficiency was attributed to a ruthenation via cmiceiled metalation and deprotonation [(Eq. 11)] [77]. 

Similarly, 5-aminoaryl-4-phenyl-triazoles 31 were prepared in moderate to good yields by condensation of various primary amines with 2-ethoxy-1-aryl-2-piperidino-l-ethenediazonium hexachloroantimonate 30 in diethylether (Scheme 10) [43]. 

C2N3 N N N — — l,3-Dimethyl-4-(l,2,3-triazolyl) sulfide 3-methyl-2-phenyl-l,2,3-triazol-l-ine-4-thione... 

Ring substituents can have a considerable effect on the acidity of the system. In the 1,2,4-triazole series a 3-amino group decreases the acidity to 11.1, a 3-methyl group to 10.7, whereas a 3-phenyl group Increases the acidity to 9.6, and 3,5-dlchloro substitution to 5.2 (71PMH(3)1). 

Despite the weak basicity of isoxazoles, complexes of the parent methyl and phenyl derivatives with numerous metal ions such as copper, zinc, cobalt, etc. have been described (79AHC(25) 147). Many transition metal cations form complexes with Imidazoles the coordination number is four to six (70AHC(12)103). The chemistry of pyrazole complexes has been especially well studied and coordination compounds are known with thlazoles and 1,2,4-triazoles. Tetrazole anions also form good ligands for heavy metals (77AHC(21)323). 

N-Unsubstituted 1,2,3-triazoles are methylated mainly in the 1-position with methyl iodide and silver or thallium salts, but mainly in the 2-position by diazomethane. There is also some steric control. For example, 4-phenyl-l,2,3-triazole with dimethyl sulfate gives the 2-methyl-4-phenyl (38%) and l-methyl-4-phenyl isomers (62%), but none of the more hindered 1-methyl-5-phenyltriazole (74AHC(16)33). JV-Unsubstituted 1,2,4-triazoles are generally alkylated at N-1. 

Enamines and enolate anions react with benzofuroxan to give quinoxaline di-A -oxides (Scheme 38) (69AHC(10)1). Sydnones (274) with phenyl isocyanate give 1,2,4-triazoles (275) (76AHC(19)l), and from (276) the intermediate adduct (277) can be isolated (73JA8452). This is one of the few instances in which such primary cycloadducts have been isolated in the oxazole series of mesoionic compounds. 

Oxidation of the hydrazone of 2-hydrazinopyrazole (226) with Pb(OAc)4 in CH2CI2 is a two-step reaction. The azine (227) was formed as an intermediate and this underwent ring closure to the 3H-pyrazolo[5,l-c][l,2,4]triazole (228) (79TL1567). A similar reaction applied to the benzal derivative of 2-hydrazinobenzothiazole (229) gave 3-phenyl-[l,2,4]triazolo[3,4-6]benzothiazole (230) together with a by-product (231) (72JCS(P1)1519). 

The 1-azirines obtained from the vapor phase pyrolysis of 4,5-disubstituted 1-phthalimido-1,2,3-triazoles (157) have been found to undergo further thermal reactions (71CC1S18). Those azirines which contain a methyl group in the 2-position of the ring are cleaved to nitriles and phthalimidocarbenes, whereas those azirines which possess a phenyl substituent in the 2-position rearrange to indoles. 

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