1 -Acetyl-1,2,4-triazole

Whereas under the conditions specified above JV-acetylpyrrole, like a typical acetamide, is not detectably hydrolyzed in neutral aqueous medium, the half-life of N-acetylpyrazole is 908 min, and that of A-acetylimidazole is reduced to 41 min for 1-acetyl-1,2,4-triazole and for the isomeric 1-acetyl-1,2,3-triazole, half-lives of 6.4 and 26.6 min, respectively, were observed (for an explanation of the different reactivities of the two pairs of isomers see above). Hydrolysis of TV-acetyltetrazole under the same conditions occurs too rapidly to be measured with conventional spectroscopic techniques. The reaction enthalpy AH was determined for A-acetylimidazole to be — 4.83 kcal/mol for the corresponding 1,2,4-triazolide the value was — 7.29, and for the tetra-zolide — 10.31 kcal/mol. 111... 

NMR has also been used as a basis for distinguishing 1- and 2-acetyl-triazoles - - and for investigating ring-chain tautomerism in tri-azoles. - - 0-H coupling constants are a useful means of determining the site of methylation of triazolo oxides, and triazolo sulfides. -... 

Triazoles are acylated with acyl halides, usually initially at the 1-position, but the acyl group may migrate to the 2-position on heating or on treatment with base. Thus acetylation with acetyl chloride often gives 1-acetyl derivatives, which rearrange to the 2-isomers above 120 °C (74AHCil6)33). 

Triazole, 5-amino-acetylation, 5, 696 acylation, 5, 696 diazotization, 5, 97 4-substituted... 

As shown by Heindel and Corley (1979), ring closure also takes place if the nucleophilic nitrogen is part of a heterocycle, as in the diazotization of 5-amino-3-methyl-2-H-l,2,4-benzothiadiazine-l, 1-dioxide (6.50). In the tricyclic compound 6.51 formed initially, the thiadiazinedioxide ring is opened rapidly in water, forming 1-acetyl-7-aminosulfonyl-l-i/-benzo-l,2,3-triazole (6.52). 

A three-component coupling was used to prepare a series of 1,4-disubstituted-l,2,3-triazoles 129 from the corresponding acetylated Baylis-Hillman adducts 127, sodium azide and terminal alkynes 128 <06TL3059>. This same reaction was also carried out in either water or in... 

The formation of triazoles by acid-catalyzed ring opening and isomerization of various other C4-substituted sydnones has also been explored <2001MI769>. When applied to 3-(2-acetylphenyl)sydnone, conditions that are successful for C4 acylation of other 3-arylsydnones result unexpectedly in the formation of the jV-acctyl-3-methylindazole 72. Initial protonation of the carbonyl in the ortho-acetyl group triggers attack by the N2 position of the sydnone ring and concludes with hydrolysis and loss of carbon dioxide (Equation 3) <1996SC2757>. 

Deacetylation of l-acetyl-3-aryloxymethyl-6-methyl-pyrazolo [5,l-c][l,2,4]triazoles 54 is achieved with sodium hydroxide to give 3-aryloxymethyl-6-methyl-177-pyrazolo[5,l-4[l,2,4]triazoles 53 (Equation 32) <2003IJC(B)2054>. 

Reaction of ethyl 5-amino-3-methylthio-l//-pyrazol-4-carboxylate 267 with sodium nitrite in the presence of hydrochloric acid gives the diazo intermediate 268, which on treatment with active methylenic compounds such as ethyl a-chloroacetate or a-chloroacetylacetone affords the hydrazonyl chlorides 269 and 270, respectively, whose reaction with triethylamine in refluxing ethanol convert them into ethyl 4-hydro-2-methylthiopyrazolo[5,l-c]-[l,2,4]triazole-3,6-dicarboxylate 271 and ethyl 6-acetyl-4-hydro-2-methylthiopyrazolo[5,l-c][l,2,4]triazole-3-carboxy-late 272 (Scheme 23) <2001MI1>. 

The reaction of 2-anilino-l,4-naphthoquinone 374 with benzoylacetic acid hydrazide gives 3-hydrazino-pyrazolyl derivative 375, that is acetylated to produce 5-[[l,4-dihydro-l,4-dioxo-3-(phenylamino)-2-naphthalenyl]sulfonyl]-3-methyl-6-phenyl-5/7-pyrazolo[5,l-c][l,2,4]triazole 51. This latter derivative is also obtained in 51% yield from reaction of 374 with benzoylacetic acid hydrazide in the presence of a mixture of acetic acid-sodium acetate <2004PS(179)1907> (Scheme 39). 

The reaction of a solution 2-hydrazinobenzothiazoles in DMF with formic acid, benzoyl chloride, or acetyl chloride, in the presence of potassium carbonate, gave the 8-fluoro-9-substituted-[l,3]-benzothiazolo[5,l-3]3-substi-tuted-1,2,4-triazoles in good yield, as shown for 6-fluoro-7-(2 -nitrophenylamino)-2-hydrazinobenzothiazole 395 yielding compound 396 (Equation 75) <2004IJH89>. 

Triazolotriazepinones 475, obtained by reaction of 4,5-diamino-3-aryloxymethyl-l,2,4-triazoles 474, on heating with acetic anhydride undergo ring contraction reaction to yield l-acetyl-3-aryloxymethyl-6-methyl-pyrazolo[5,l-f][ 1,2,4]triazoles 476 (Scheme 54) <2003IJC(B)2054>. This type of transformation has been previously documented by other authors <1974JHC751>. 

Alkylation or acylation takes place at the nitrogen in position 1 when l/7-[l,2,4]triazolo[4,3-A][l,2,4]triazole 9 is treated with methyl iodide or acetyl chloride, furnishing compound 10 or 11, respectively <1983S415>. The 7-methyl isomers 13 are obtained after conversion of compounds 9 into the 1-acetyl derivatives 11 followed by methylation with methyl trifluoromethanesulfonate to give the l-acetyl-6-aryl-7-methyl-3-methylthio-17/-[l,2,4]triazolo[4,3-A]-[l,2,4]triazol-7-ium-trifluoromethanesulfonates 12, which upon treatment with aqueous sodium carbonate afford the 7-methyl derivatives 13 <1985BCJ735>. 

Glycosylation of 3-amino-5(7)//-[l,2,4]triazolo[4,3-3] l,2,4 triazole 17 with 1-O-acetyl- 2,3,5-tri-O-benzoyl-D-ribo-furanose 18 or 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide 19 can be selective or nonselective, depending on the reaction conditions (Scheme 1). In the presence of trimethylsilyl triflate or boron trifluoride etherate, the... 

The Schiff base derivatives 73 of the 3-hetaryl-substituted 4-amino-3-thiol-l,2,4-triazoles, on treatment with acetic anhydride, undergo cyclization to give the corresponding 3-substituted-5-acetyl-5,6-dihydro-6-phenyl[l,2,4]triazolo[3,4-7][l,3,4]thiadiazoles 76 (Equation 16) <1990IJB135>. Similar treatment of 4-(A-bcnzoylamino)-4,5-dihydro-l-methyl-3-mcthylthio-1 //-[ 1,2,4 triazolc-5-thione 77 leads to the [l,2,4]triazolo[3,4-4][l,3,4]thiadiazolium trifluoromethanesulfonate 78 (Equation 17) <1986LA1540>. 

Triazoles (386, R1 = COOMe) were treated with potassium tert-butylate in a mixture of f r/-butanol and benzene for 15-60 min to give (substituted amino)methoxycarbonylmethylenemalonates (387, R1 = COOMe) in 28-54% yields. In the case of the acetyl derivative (386, R = Ph, R1 = COMe), the reaction was carried out in chloroform in the presence of triethylamine at ambient temperature for 8 hr, to give (pheny-lamino)acetylmethylenemalonate (387, R = Ph, R = COMe) in 38% yield. (Phenylamino)acylmethylenemalonates (387, R = Ph,R = COMe, COPh) were also prepared in 62-74% yields when diazo derivatives (388, R1 = COMe, COPh) were heated in benzene for 4-24 hr (80T1821) (Scheme 34). 

Very few 2/f-triazole syntheses involve azides, apart from those (such as 2-acetyl derivatives) which involve prior formation and rearrangement of IjEf-triazoles. Some vinyl diazides react with triphenyl-phosphine in mild conditions to give iminophosphoranes of 2-amino-triazoles (Scheme 36). ... 

A study of the photochemistry of 4-acetyl- and 4-benzoyl-5-methyl-1,2,3-triazoles shows that the nature and lifetime of the lowest triplet state depends on the nature of the 1- and 4-substituents. 4-Benzoyl-5-methyl-1,2,3-triazole has a high rate constant for triplet deactivation, which is attributed to interaction of the nitrogen lone pairs with the excited carbonyl function. The compound forms a pinacol derivative when irradiated in propan-2-ol and undergoes cycloaddition, involving the carbonyl group, with 2-methylpropene, giving an oxetane derivative. 

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