1,2,4-Triazoles. Improved synthesis of 5-substituted 4-amino-3-mer-cato-(4H)-1,2,4-triazoles and a facile route to 3,6-disubstituted 1,2,4-triazolo[3,4-b][1,3,4]thiadiazoles

The reaction of thiocarbohydrazide with carboxylic acids at the melting temperature allows an improved preparation of the S-substituted 4-amino-3-mercapto-1,2,4-triazole heterocycles. The crude 4-amino-5-mercapto-1,2,4-triazoles react easily with carboxylic acids or carboxylic acid chlorides to afford the 1,2,4-triazolo[3,4-fc][1,3,4]thiadiazole ring system.     

On Triazoles. XIII. The reaction of 5-benzalimino-1,2,4-triazoles with substituted acetyl chlorides

The reaction of Schiff bases prepared from 1- and 2-substituted-5-amino-1,2,4-triazoles with phenoxyacetyl chlorides in the presence of triethylamine and a mixture of phosphorus oxychloride and dichloroacetic acid in dimethylformamide to yield β-lactam 4 , a dihydro-1,2,4-triazolo[4,3-a]pyrimidine-5(1H)-one 5, a 1,2,4-triazolo[1,5-a]pyrimidin-5(3H)-one 9 and the corresponding 1,2,4-triazolo[4,3-a]pyrimidine-5(1H)-one 10 derivatives was studied.     

Synthesis of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines and 4-amino-3-acylvinylthio-1,2,4-triazoles by reaction o acylacetylenes with 4-amino-3-mercapto-1,2,4-triazole

1,2,4-Triazolo[3,4-b]-1,3,4-thiadiazepines have been prepared by treating -acetylenic ketones with 4-amino-3-mercapto-1,2,4-triazole in glacial acetic acid. Terminal acetylenic ketones react with the triazole to form 4-amino-3-acylvinylthio-1,2,4-triazoles. Heating the latter with hydrazine hydrate in alcohol yields substituted pyrazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 990–994, July, 1991.     

Improved syntheses of 5-substituted-4-amino-3-mercapto-(4H)-1,2,4-triazoles

Two improved methods have been developed for the synthesis of 5-substiluted-4-amino-3-mercapto-(4H)-1,2,4-triazoles. One of these involves the direct hydrazinolysis of potassium 3-aroyldithiocarbazates and the other involves ring-opening and reclosure of 5-substituted-2-mereapto-1,3,4-oxadiazoles to the aminomercaptotriazoles. Both of these methods offer advantages over the classic Hoggarth synthesis.     

Syntheses of substituted-oxazolo-1,3,4-thiadiazoles, 1,3,4-oxadiazoles,and 1,2,4-triazoles

Starting from readily available methyl 5-methyloxazole-4-carboxylate ( 1 ) and 4-methyl-5-oxazolylcar-boxylic acid hydrazide ( 11 ) the title compounds were prepared. The reaction of compound 1 with hydrazine hydrate afforded the corresponding hydrazide 2 . The reaction of compound 2 with formic acid yielded 1-formyl-2-(5-methyloxazole-4-carboxyl)hydrazine ( 3 ). Refluxing of the latter with phosphorus pentasulfide in xylene gave compound 5 in 62% yield. The reaction of compound 3 with phosphorus pentoxide afforded compound 4 . Starting from hydrazide 11 , compounds 13 and 14 were prepared similarly. Reaction of compound 2 with substituted isothiocyanate yielded compound 9 which was cyclized in basic medium to 4-alkyl-5-(5-methyl-4-oxazolyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione ( 10 ). The isomer 19 was prepared similarly. Methylation and subsequent oxidation of compound 19 gave compound 21 . Reaction of the acid 7 with thiosemicarbazide in the presence of phosphorus oxychloride gave 2-amino-5-(5-methyl-4-oxazolyl)1,3,4-thiadiazole ( 8 ). 2-Amino-5-(4-methyl-5-oxazolyl)-1,3,4-thiadiazole ( 17 ) was prepared from acyl chloride 15 by the usual method.     

Synthesis of 2-amino-5-(5R-1,2,4-oxadiazolyl-3)-1,3,4-oxadiazoles

The interaction of 2-amino-1,3,4-oxadiazole-5-carboxamidoxime with nitriles in the presence of ZnCl₂ and HCl or with trichloroacetic anhydride affords 2-amino-5-(5R-1,2,4-oxadiazolyl-3)-1,3,4-oxadiazoles. Their reactions with N-nucleophiles have been studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2100–2103, December, 1993.     

Conversion of 2-amino-5-R-phenyl-1,3,4-oxadiazoles into 3-R-phenyl-5-alkoxy-1,2,4-triazoles

2-Amino-5-R-phenyl-1,3,4-oxadiazoles have been shown to isomerize in alcoholic potassium hydroxide solution to 3-R-phenyl-5-alkoxy-1,2,4-triazoles. The dissociative ionization of 3-R-phenyl-5-alkoxy-1,2,4-triazoles and 3-R-phenyl-1,2,4-triazolin-5-ones has been examined. The mass spectra of the oxadiazoles have been compared with those of the triazoles.Translated from Khimiya Geterotslklicheskikh Soedinenii, No. 11, pp. 1553–1556, November, 1986.     

Formation of substituted 1,2,4-triazoles and 3h- 1,3,4-benzotriazepines from 5-aryltetrazoles and N-arylbenzimidoyl chlorides (review)

The review discusses the results obtained in the synthesis of substituted 1,2,4-triazoles and 3H-1,3,4-benzotriazepines from 5-aryltetrazoles and N-arylbenzimidoyl chlorides. The farther possibilities of obtaining 3H-1,3,4-benzotriazepines, the mechanism of their formation, and the physical and chemical properties have been assessed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 907–912, July, 1993.     

1-Hydrazonyltetrazoles: Fragmentative cyclisation - a new route to substituted 1,2,4-triazoles.

The reaction of tetrazole and some 5-aminotetrazoles with C-phenyl-N-4-nitrophenyl-nitrileimine gave 1-hydrazonyltetrazoles which fragmented and cyclised to 1,2,4-triazoles with overall loss of HN₃.     

Photochemistry of fluorinated heterocyclic compounds. An expedient route for the synthesis of fluorinated 1,3,4-oxadiazoles and 1,2,4-triazoles

The photochemistry of some 3-N-alkylamino-5-perfluoroalkyl-1,2,4-oxadiazoles in the presence of nitrogen nucleophiles such as ammonia and primary and secondary aliphatic amines has been investigated. The primary photolytic intermediate from the cleavage of the ring O-N bond follows two distinct and competing pathways leading to (i). 5-perfluoroalkyl-1,3,4-oxadiazoles, through the ring contraction-ring expansion photoisomerization route favored by the presence of the base or (ii). 5-perfluoroalkyl-1,2,4-triazoles, through the intervention, as an internal nucleophile, of the exocyclic N-alkylamino moiety of the oxadiazole followed by the attack of the external nitrogen nucleophile and subsequent heterocyclization. Some comments on the photoreactivity of fluorinated oxadiazoles and on the applications of these photoprocesses in the synthesis of target fluorinated structures are emphasized. In this context, irradiations of 3-perfluoroalkanoylamino-4-phenylfurazan in the presence of primary aliphatic amines are reconsidered as feasible one-pot synthetic methodologies toward fluorinated heterocycles. X-ray analysis of two representative products 1-methyl-3-methylamino-5-perfluoroheptyl-1,2,4-triazole and 2-methylamino-5-trifluoromethyl-1,3,4-oxadiazole confirmed the proposed structures and furnished interesting information on the crystal packing of these fluorinated five-membered heterocycles.     

The synthesis of 3- and 5-amino-1,2,4-oxadiazoles. A caveat

Evidence obtained from a single series of compounds demonstrates the need for care when assigning structures to amino-1,2,4-oxadiazoles using the methodology described in the literature. Certain synthetic methods can give rise to different position isomers in different series.     

Hypervalent iodine(V) mediated mild and convenient synthesis of substituted 2-amino-1,3,4-oxadiazoles

A simple protocol for the synthesis of 2-amino-1,3,4-oxadiazoles starting from the corresponding acylhydrazides by cyclodesulfurization of intermediate acylthiosemicarbazides mediated by o-iodoxybenzoic acid in good yields has been described. The protocol is mild with wide substrate scope, and thus a range of 2-amino-1,3,4-oxadiazoles have been prepared.     

3-(3-吡啶基)-4-氨基-5-芳胺基-1,2,4-三唑的合成与表征

以烟酸与芳胺为基本原料，经多步反应，制得1－烟酰基－4－芳基氨基硫脲；后者在水合肼存在下关环，合成了一系列新化合物3－（3－吡啶基）－4－氨基－5－芳胺基－1，2，4－三唑。化合物结构经元素分析、IR，^1H NMR,^13C NMR确证。     

Synthesis and antimicrobial activity of pyrrolyl/pyrazolyl arylaminosulfonylmethyl 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and 1,2,4-triazoles

A new class of pyrrolyl/pyrazolyl arylaminosulfonylmethyl 1,3,4-oxadiazoles, 1,3,4-thiadiazoles, and 1,2,4-triazoles were prepared and tested for antimicrobial activity. Amongst the tested compounds, 5c displayed high antimicrobial activity.     

On triazoles. XXXV. The reaction of 5-amino-1,2,4-triazoles with di- and triketones

The reaction of 5-amino-3-Q-1H-1,2,4-triazoles 1 with aliphatic, aromatic and cyclic 1,3-diketones, 1,4-diketones, and different linear and non linear triketones was studied. It was proved that in case of unsym-metrical aliphatic 1,3-diketones the regiochemical outcome of the reaction was influenced by steric factors. In case of triacetylmethane and 3-(4-chlorobenzyl)-2,4-pentanedione the splitting of one acetyl group from the reactant was observed during the reaction. A liner triketone, namely the 2,4,6-trioxoheptane reacted as a simple 1,3-diketone.     

5-(Thiazol-4-yl)-1,2,4-triazoles

By reaction of arylhydrazones of benzoyl chloride with 4-aminomethylthiazole in the presence of triethylamine, the corresponding amidrazones were obtained, which upon oxidation gave 5-(thiazol-4-yl)-1,2,4-triazoles with fungicidal and bactericidal activity.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2111–2112, September, 1991.     

Synthesis and biological evaluation of novel 2-(substituted isoxazol-4-yl)-5-arylamino-1,3,4-oxadiazoles

A series of 2-(5-methyl-3-(4-chloro/trifluoromethylphenyl)isoxazol-4-yl)-5-arylamino-1,3,4-oxadiazoles were synthesized from 4-chloro/trifluoromethyl benzaldehyde, ethyl acetoacetate, hydroxylamine hydrochloride, hydrazine hydrate, and aryl isocyanate by multi-step reactions. The structures of the target compounds were elucidated by IR, ¹H NMR, MS, and elemental analysis. All these compounds were tested for in vitro antifungal activities against Botrytis cinerea and Rhizoctonia cerealis by the mycelium growth rate method, and the results indicated that some compounds displayed high antifungal activity against Botrytis cinerea.     

4-Amino-3-mercapto-4H-1,2,4-triazoles and propargyl aldehydes: A new route to 3-R-8-aryl-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines

The pendant amino and mercapto groups on 4-amino-3-mercapto-4H-4H-1,2,4-triazoles can be cyclized by phenylpropargyl aldehydes. The aldehydes experience Michael addition of the SH to the alkyne linkage and imine formation between the NH₂ and the aldehyde carbonyl to produce 3-R-8-aryl-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines.     

Fluorescence and liquid scintillation properties of 1,3,4-oxadiazoles. I. Excimer formation in 2-alkyl-5-(4-biphenylyl)-1,3,4-oxadiazoles

Several 2-alkyl-5-(4-biphenylyl)-1,3,4-oxadiazoles have been synthesized and investigated as primary liquid scintillation solutes and are found to be excellent fluors. Fluorescence studies at varying concentrations and temperatures indicate that excimer formation is possible at high concentration and low temperatures.