Novel syntheses of symmetrical 2,5-diaryl-1,3,4-oxadiazoles and 1,4-phenylenebis-1,3,4-oxadiazoles

The reactions of trichloromethylarenes with excess hydrazine hydrate in ethanol gives symmetrical 2,5-diaryl-1,3,4-oxadiazoles in 68–96% yields. The reaction of 1,4-bis(trichloromethyl)benzene with acylhydrazines in an ethanol-pyridine mixture gives the corresponding substituted or unsubstituted 1,4-phenylenebis-1,3,4-oxadiazoles in 35–51% yields. The mass spectra of 2,5-diaryl-1,3,4-oxadiazoles and 1,4-phenylenebis-1,3,4-oxadiazoles were studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2309–2316, November, 1998.     

Reactions of trichloromethylarenes with hydrazine derivatives. Synthesis of 2,5-disubstituted 1,3,4-oxadiazoles and 1,3,4-thiadiazoles

The effect of the solvent on the course of the reaction between trichloromethylarenes and thioacylhydrazines or acylhydrazines has been considered. In alcohols as solvents, alkyl arenecarboxylates form as a result of alcoholysis, while 2,5-disubstituted 1,3,4-thiadiazoles (1,3,4-oxadiazoles) form as minor products. In pyridine solutions, the major or sole products are those of reductive condensation,i.e., the correspondingN-substituted hydrazones of arenecarbaldehydes. 1,3,4-Thiadiazole or 1,3,4-oxadiazole derivatives are obtained in good yield when the reaction is carried out in a pyridine-alkanol mixture.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1246–1249, May, 1996.     

Synthesis and Fungicidal Activity of 1,3,4-Oxadiazole Substituted Acylthioureas

A series of N′-(5-aryl-1,3,4-oxadiazole-2-yl) actylthioureas have been synthesized from p-chlorophenoxyacetic acid, and then substituted 2-amino-5-aryl-1,3,4-oxadiazoles reacting with acylthiocyanoester, which are derived from the second step, are used. Their structures are confirmed by Infrared, ¹H nuclear magnetic resonance, and elementary analysis. From biological testing, it is found that some of these compounds have good fungicidal activity. Translated from Chemical Research and Application, 2005, 17(2) (in Chinese)     

An efficient synthesis of new 2-aminomethyl-1,3,4-oxadiazoles from enantiomeric phenylglycine hydrazides

New derivatives of 2-aminomethyl-1,3,4-oxadiazole were synthesized in the reactions of N-protected phenylglycine hydrazides and triethyl orthoesters (orthoformate, orthoacetate, orthopropionate, orthobenzoate) in the presence of glacial acetic acid. Studies on the cleavage reactions of the acid-sensitive N-BOC and N-Ac 1,3,4-oxadiazoles are presented. Spectral characteristics of the compounds and attempts to elucidate the racemization phenomenon observed in products are also discussed.     

含双1,3,4-噁二唑类荧光化合物的合成及荧光性能

在丙基磷酸酐催化条件下,由对甲基苯甲酸和取代苯甲酰肼通过环合反应得到含甲基的1,3,4-噁二唑单环,经高锰酸钾氧化反应得到单环1,3,4-噁二唑芳香酸;然后再次利用丙基磷酸酐的催化效应,实现芳香酸与邻羟基苯甲酰肼的环合反应,制备得到含双1,3,4-噁二唑结构的荧光化合物.利用红外光谱仪和核磁共振谱仪表征了合成产物的结构,并测定了产物的元素组成和荧光性能.结果表明,各合成产物的总收率为44%～49%;目标化合物具有较大的Stokes位移.     

Cyclodesulfurization of Substituted Thiosemicarbazides into 1,3,4-Oxadiazoles via Hydrazonoyl Chlorides

Abstract

The reaction of thiosemicarbazides 1a–h with hydrazonoyl chlorides 2a–g at ambient temperature, in the presence of triethylamine yielded, in each case, two products. The structure of these compounds was confirmed as 1,3,4-oxadiazoles 14a–h and hydrazonothioates 15a–g. The structure of 15b was confirmed through single crystal X-ray diffraction. A mechanism was proposed for this cyclodesulfurization reaction.     

An efficient synthesis of conjugated 5-aryl-1,3,4-oxadiazoles from 3-heteroarylacrylohydrazides and acid chlorides

New derivatives of 5-aryl-2-[2-(2-furyl)ethenyl]-1,3,4-oxadiazoles and 5-aryl-2-[2-(2-thienyl)ethenyl]-1,3,4-oxadiazoles are synthesized in a stepwise procedure through intermediate acyclic N′-arylcarbonyl-N-[2-(2-heteroaryl)acryloyl]hydrazines, starting from 3-(2-heteroaryl)acrylic acid hydrazides and acid chlorides. A facile one-pot methodology leading to the final 1,3,4-oxadiazoles is also described.     

An expeditious,solvent-free synthesis of some 5-aryl-2-(2-hydroxyphenyl)-1,3,4-oxadiazoles

An efficient, rapid, microwave-accelerated one-step synthesis of some 5-aryl-2-(2-hydroxy-phenyl)-1,3,4-oxadiazoles by reaction of salicylic hydrazide with carboxylic acids in the presence of thionyl chloride under neat conditions is described. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1264–1267, August, 2007.     

Two reaction routes for the preparation of aromatic polyoxadiazoles and polytriazoles: Syntheses and properties

Two reaction routes for the preparation of aromatic poly-1,3,4-oxadiazoles and poly-1,2,4-triazoles are studied and their influence on the physical properties, i.e., inherent viscosity, glass transition, degradation temperature, and film integrity of the final products are discussed. Aromatic poly-1,3,4-oxadiazoles are prepared by means of a polycondensation reaction of terephthaloyl chloride and isophthalic dihydrazide yielding a precursor polymer, poly(p, m-phenylene) hydrazide, which is converted into the corresponding poly-1,3,4-oxadiazole by means of a cyclodehydration reaction. Poly-1,3,4-oxadiazoles are also prepared by means of a polycondensation reaction between terephthalic and isophthalic acid and hydrazine yielding poly-1,3,4-oxadiazoles with higher inherent viscosities. Flexible poly-1,3,4-oxadiazole films are obtained only if the inherent viscosities of the polymers used are higher than 2.7 dL/g. The thermal stability is found to increase with increasing content of p-phenylene groups in the polymer backbone. Aromatic poly-1,2,4-triazoles are prepared using polyhydrazides with alternating para- and meta-phenylene groups and poly-1,3,4-oxadiazoles with a random incorporation of para- and meta-phenylene groups in the main chain as precursor polymers. The glass transition temperatures are found to increase with increasing content of p-phenylene groups in the main chain of these polymers. Cold crystallization is observed only for the alternating polymer. © 1994 John Wiley & Sons, Inc.     

The Reaction of 5-Aryl(hetaryl)-2-aroylmethylthio-1,3,4-oxadiazoles with Aryldiazonium Tetrafluoroborates

5-Aryl(hetaryl)-2-aroylmethylthio-1,3,4-oxadiazoles behave as CH acids and readily react with aryldiazonium tetrafluoroborates at the active methylene group to give azo coupling products. The spectroscopic properties of the compounds synthesized have been studied.     

An expeditious and one-pot synthesis of unsymmetrical 2,5-disubstituted-1,3,4-oxadiazoles under microwave irradiation and solvent-free conditions

A one-pot synthesis of some unsymmetrical 2,5-disubstituted-1,3,4-oxadiazoles via cyclocondensation of benzoylhydrazines with orthoesters under solvent-free and microwave conditions are described here. The reaction is efficiently catalyzed by silica- supported sulfuric acid as it provided the title compounds in high yields and relatively short times. The catalyst is reusable and can be applied several times without considerable decrease in the yields and rates of the reactions.     

Synthesis of picryl-substituted 1,3,4-oxadiazoles

A convenient procedure was developed for the synthesis of picryl-substituted 1,3,4-oxadiazoles. The nucleophilic replacement of the nitro group in picroylacylhydrazines under the action of thiophenol was studied. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1583–1585, September, 2000.     

Microwave-Assisted Synthesis and Antifungal Activity of 2,5-Disubstituted-1,3,4-oxadiazoles Containing Azulene Moiety

Microwave-assisted as well as conventional synthesis of 2,5-disubstituted-1,3,4-oxadiazoles containing the azulene moiety was carried out, and their antifungal activity is also reported.     

Intramolecular cycloaddition of fluorinated 1,3,4-oxadiazoles to dienes

Cycloaddition reactions of fluorinated 1,3,4-oxadiazoles with conjugated and unconjugated dienes was studied. The reactions resulted in the formation of products of double cycloaddition (7-oxabicycloheptane type compounds), along with products of intramolecular cycloaddition (oxatricyclic and oxatetracyclic compounds). The structure of 4-(trifluoromethyl)-2-ethoxycarbonyl-1,6-dimethyl-3-oxatricyclo[2.2.1.0^2,6]heptane was confirmed by single crystal X-ray diffraction analysis.     

A new approach to the one-pot synthesis of 5-substituted 2-methyl-1,3,4-oxadiazoles from N-tributylstannyltetrazoles

A new approach to the synthesis of 5-substituted 2-methyl-1,3,4-oxadiazoles was developed.     

Mild and convenient one-pot synthesis of 1,3,4-oxadiazoles

A mild, general, convenient, and efficient one-pot synthesis of 2-phenyl-5-substituted-1,3,4-oxadiazoles is described. Both (hetero)aryl and alkyl carboxylic acids were efficiently condensed with benzohydrazide in the presence of TBTU to give diacylhydrazine intermediates. The latter underwent a smooth TsCl-mediated cyclodehydration reaction to afford 2-phenyl-5-substituted-1,3,4-oxadiazoles in good to very good yields.     

Trimethylsilyl-1,3,4-oxadiazoles—new useful synthons for the synthesis of various 2,5-disubstituted-1,3,4-oxadiazoles

The reactivity of 2-aryl-5-trimethylsilyl-1,3,4-oxadiazoles toward different types of electrophiles was investigated. These silanes readily react with chlorine, bromine, aliphatic acyl chlorides, 2-nitrobenzenesulfenyl chloride, and some reactive isocyanates affording the corresponding substituted 1,3,4-oxadiazoles. The reactions with carbonyl compounds proceed only in the presence of F⁻ anions.     

Recyclization of 1,3,4-Oxadiazoles and Bis-1,3,4-oxadiazoles into 1,2,4-Triazole Derivatives. Synthesis of 5-Unsubstituted 1,2,4-Triazoles

Efficient methods have been developed for obtaining precursors of stable carbenes, viz. 5-unsubstituted 3,4-diaryl-1,2,4-triazoles and 3,3′- or 4,4′-bridge linked bis-1,2,4-triazoles, by the recyclization of 5-unsubstituted 1,3,4-oxadiazoles or p-phenylenebis-1,3,4-oxadiazole with anilines or aromatic diamines in the presence of trifluoroacetic acid or with aniline hydrochlorides in pyridine. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1026–1032, July, 2005.     

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.     

Synthesis of 2,5-disubstituted 1,3,4-oxadiazoles containing benzothiazolylthiol grouping

A series of 2,5-substituted 1,3,4-oxadiazoles containing 2-benzothiazolylthiomethyl grouping has been synthesized by condensing derivatives of (2-benzothiazolylthio)acetic acid with imino ester hydrochlorides and hydrazides of carboxylic acids, by the cyclodehydration of N-acyl-N-(2-benzothiazolylthioacetyl)hydrazines under the action of POCl, and also by the reaction of 2-mercaptobenzothiazole with 2-chloromethyl-1,3,4-oxadiazoles in the presence of sodium methylate.I. M. Gubkin Russian State University for Petroleum and Gas, Moscow 117917. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 249–255, February, 2000.