Synthesis of 2,5-disubstituted 1,3,4-oxadiazoles containing a sterically hindered 4-hydroxy-3,5-di(tert-butyl)phenyl group

A series of 2,5-disubstituted 1,3,4-oxadiazoles containing one or two 4-hydroxydi(tert-butyl)phenyl groups has been synthesized. These sterically hindered compounds were prepared by condensation of acids containing the indicated fragment and their derivatives with hydrazine dihydrochloride, hydrazides, and hydrochlorides of iminoesters of acids, by the reaction of 4-hydroxy-3,5-di(tert-butyl)thiphenol with 2-chloromethylsubstituted 1,3,4-oxadiazoles in the presence of KOH, and by cyclodehydration of N-acyl-N-[4-hydroxy-3,5-di(tertbutyl)benzoyl]hydrazones under action of POCl₃.I. M. Gubkin State Oil and Gas Academy, Moscow 117917. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 822–828, June, 1997.     

Synthesis of di- and trisubstituted 1,2,4-triazoles containing indole fragments

The reaction of imino esters of indole-series acids with acid hydrazides gave N₍₁₎-acylamidrazones, which, during heating, were converted to 3,5-disubstituted 1H-1,2,4-triazoles containing indole fragments. Compounds of this type were also synthesized by the reaction of indolyl-containing 2,5-disubstituted 1,3,4-oxadiazoles with formamide. Condensation of 2,5-disubstituted 1,3,4-oxadiazoles with aniline gave 3,4,5-trisubstituted 4H-1,2,4-triazoles containing indolyl radicals. Cyclocondensation of N₍₁₎-phenylamidrazones of indole-series acids with benzoyl chloride gave 1,3,5-trisubstituted 1H-1,2,4-triazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 189–196, February, 1993.     

Synthesis and study of poly (1, 3, 4-oxadiazoles)

Various conditions for synthesizing poly (1,3,4-oxadiazoles) from carboxylic acids, their hydrazides, and polyhydrazides, are investigated. Methods of cyclodehydration of polyhydrazides using phosphorus oxychloride, sulfuric acid, and certain other reagents are not of general utility for synthesizing poly (1,3,4-oxadiazoles). Vacuum-heating polyhydrazides gives crosslinked polymers. A new method of preparing poly (1,3,4-oxadiazoles) is offered. It is the reaction of hydrazine sulfate or dihydrazides of acids with dicarboxylic acids in oleum solution. Some chemical properties of the compounds synthesized are investigated.     

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.     

A simple and efficient one step synthesis of 1,3,4-oxadiazoles utilizing polymer-supported reagents and microwave heating

1,3,4-Oxadiazoles can be rapidly and efficiently synthesized from a variety of carboxylic acids and acid hydrazides in one simple step. The use of commercially available PS-PPh₃ resin combined with microwave heating delivered the product 1,3,4-oxadiazoles in high yields and purities.     

N,N-bis (2-chloroethyl) amides and N,N-bis(2-chloroethyl) hydrazides of carboxylic acids of the furan series

Reaction of N, N-bis(2-chloroethyl)amine hydrochloride with chloroanhydrides of carboxylic acids of the furan series, in chloroform in the presence of pyridine gives N, N-bis(2-chloroethyl)amides of furan carboxylic acid, furylacrylic acid, 5-nitrofuran carboxylic acid, and 5-nitrofurylacrylic acid.N, N-bis(2-chloroethyl)hydrazides of furan carboxylic acid, furyl carboxylic acid, 5-nitrofuran carboxylic acid, and 5-nitrofurylacrylic acid were obtained in 78–88% yields by reacting N, N-bis(2-chloroethyl)hydrazine hydrochloride with the chloroanhydrides of the appropriate acids in chloroform in the presence of pyridine. The last two hydrazides were prepared in 31 % and 56 % yield, respectively, using anhydrous sodium acetate in place of pyridine.     

Synthesis of benzazoles, 1,3,4-oxadiazoles,and 1,3,4-thiadiazoles containingβ-alkylthioethyl radicals

By the condensation of hydrochlorides of iminoesters of-alkylthiopropionic acids with o phenylenediamine, o-aminophenols, hydrazides of acids, and thiosemicarbazide, we have synthesized 2-substituted benzimidazoles and benzoxazoles, 2, 5-disubstituted 1, 3, 4-oxadiazoles, and 2-amino-5-substituted 1, 3, 4-thiadiazoles containing-alkylthiioethyl fragments.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 115–118, January, 1994.     

Synthesis and properties of furan derivatives. 5. Synthesis of 2-substituted benzoxazoles containing furan fragments

The condensation of imidates and imidate hydrochlorides of furan acids with o-aminophenols gives furyl derivatives of 2-substituted benzoxazoles. Such compounds are also formed in the reaction of furan acids with o-aminophenol in the presence of boric acid.Communication 4, see [1].I. M. Gubkin State Petroleum and Gas Academy, 117917 Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 896–901, July, 1996. Original article submitted April 16, 1996.     

Synthesis of 2,5-disubstituted 1,3,4-oxadiazoles from trichloromethylarenes and acylhydrazines

A preparative synthesis of 2,5-disubstituted 1,3,4-oxadiazoles by the reaction of trichloromethylarenes with hydrazides of carboxylic acids of the aliphatic, aromatic and heteroaromatic series in methanol or ethanol in the presence of pyridine was developed.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 686–692, May, 1994. Original article submitted April 8, 1994.     

A mild and efficient one pot synthesis of 1,3,4-oxadiazoles from carboxylic acids and acyl hydrazides

A convenient one pot method for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles from acids and acyl hydrazides is reported. Acid activation with CDI, followed by coupling with the desired acylhydrazide and dehydration in the same pot with Ph₃P and CBr₄ affords the corresponding 1,3,4-oxadiazoles in good yield. The scope of the acid and acylhydrazide components is presented.     

Photochemistry of heterocyclic compounds—II : The photochemical reaction of 2,5-disubstituted 1,3,4-oxadiazoles with furan

The photochemical reaction of 2,5-disubstituted 1,3,4-oxadiazoles with furan has been studied. With or without benzophenone as a sensitizer, irradiation of 2,5-diphenyl-1,3,4-oxadiazole with furan in benzene solution gives the 1 : 1 cycloadduct, tetrahydrofuro[2·3-b]azetidino[2·1-b]-1,3,4-oxadiazole. However in the presence of iodine 3-acylfurans and their acylhydrazones are formed. A reaction pathway of this novel photo-induced acylation has been suggested.     

Synthesis of mesityl-substituted 1,3,4-oxadiazoles from mesitotrichloride and aromatic and heteroaromatic acid hydrazides

At interaction of 2,4,6-trimethylbenzotrichloride with aromatic (heteroaromatic) acid hydrazides in a mixture of 2,6-lutidine and tert-butanol the processes of alcoholysis and reductive condensation are suppressed. The corresponding 2-aryl- or 2-hetaryl-5-mesityl-1,3,4-oxadiazoles are obtained in high yields. The PMR, IR, and mass spectra of the products are studied. Dedicated to Professor Henk van der Plas on his 70th birthday. N. D. Zelinskii Institute of Organic Chemistry, Moscow 117913, Russia Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 557–563, April, 1999.     

Parallel solution phase synthesis of a library of amino acid derived 2-arylamino-[1,3,4]-oxadiazoles

A mild method for the synthesis of peptidomimetic 2-arylamino 5-substituted 1,3,4-oxadiazoles from Boc-protected α-amino acid derived hydrazides has been developed, and applied in a parallel solution-phase synthesis. The optimized reaction conditions involve a one-pot reaction of Boc-protected amino acid hydrazides with arylisothiocyanates in the presence of either Hg(II) chloride, Mukaiyama’s reagent (2-chloro-N-methylpyridinium iodide) or polymer supported Mukaiyama’s reagent, with triethylamine in dichloromethane at ambient temperature. The 1,3,4-oxadiazole products were obtained in good to excellent yields without any detectable epimerization. The reactions proceed via initial formation of thiosemicarbazides, followed by dehydrothiolative cyclization to the 1,3,4-oxadiazoles.     

A novel one-pot synthesis of 2-alkylthio-1,3,4-oxadiazoles in water

A facile and one-pot protocol for the synthesis of 2-alkylthio-1,3,4-oxadiazoles is reported. This green method relies on the reaction of acid hydrazides with CS₂ and an alkyl halide. The reaction is carried out under mild and environmentally friendly procedure in water with high to excellent yields. Thirteen different valuable alkylthio-1,3,4-oxadiazoles are synthesized from cheap and easily available CS₂ with this method. This is the first report for the synthesis of 1,3,4-oxadiazoles in water.     

Synthesis, characterization, and biological activities of some 3,5,6-trichloropyridine derivatives

Aromatic carboxylic acids on refluxing with 3,5,6-trichloro-2-pyridyloxyacetylhydrazide in POCl3 gave 5-aryl-2-(3,5,6-trichloro-2-pyridyloxymethyl)-1,3,4-oxadiazoles. The hydrazide on treatment with acid chlorides gave diacylhydrazines, whereas with arylsulfonyl chlorides acyl(arylsulfonyl)hydrazines were obtained. The latter two types of compounds were tested for their antibacterial and antifungal activities whereas 1,3,4-oxadiazole derivatives were tested for their herbicidal activity. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 711–717, May, 2006.     

Chemistry of amino acid thionoester derivatives. An unexpected change in the reaction course between heterocyclic-2-carboxylic acid hydrazides and N-substituted thionoglycinates. Preferential formation of 4-amino-1,2,4-triazole adducts over 1,3,4-oxadiazole products

The reaction between benzoic acid hydrazides and ethyl N-carbobenzyloxythionoglycinate produces the expected 2-aminomethyl-1,3,4-oxadiazoles in good yield. Heterocyclic carboxylic acid hydrazides give similar products when the hydrazide moiety is located at either the three or four position (relative to the heteroatom) in the ring. However, when heterocyclic-2-carboxylic acid hydrazides are utilized, oxadiazole formation is dramatically reduced. Instead, the intermediate imidates are usually isolated as the major products of the reaction from one equivalent of these hydrazides. These imidate products are accompanied by significant amounts of 4-amino-1,2,4-triazole derivatives which arise from incorporation of two equivalents of the hydrazide. The structure of these unexpected 4-aminotriazole products was confirmed by nmr and mass spectral data as well as an X-ray analysis. In the presence of a stoichiometric amount of these hydrazides, the 4-aminotriazoles become the major products of the reaction. This phenomenon was found to be general for 2-thienyl, 2-furoic, picolinic, and pyrazinoic acid hydrazides. The intermediate imidates for each of these systems were isolated, characterized and found to have a remarkable thermal stability. Conversion of these imidates to the corresponding 1,3,4-oxadiazoles could only be accomplished in hot acetic anhydride. A mechanistic rationale is presented which suggests that some stabilization of the intermediate imidate must occur in these examples which allows an intermolecular process to compete so effectively with an intramolecular cyclization. Since the cyclization to oxadiazole is presumed to be acid catalyzed, this stabilization is proposed to occur specifically by the formation of a hydrogen bond between the ring heteroatom and the proton-ated imino nitrogen present in the imidate prior to cyclization. The formation of such a hydrogen bond removes the carboxylate oxygen from its opportune position for cyclization, while the protonated imino nitrogen can still activate the imidate for subsequent reaction with a second equivalent of hydrazide. In all cases where this heteroatom is capable of hydrogen bond formation, 4-aminotriazoles predominate. The relative amount of 4-aminotriazole product is directly correlatable with the donor capability of the ring hetero-atom. This proposed model was tested by examining a system where steric congestion would be expected to prevent hydrogen bond formation. Indeed, when N-methyl-2-pyrrole carboxylic acid hydrazide was utilized in the reaction, the corresponding 1,3,4-oxadiazole was formed as expected in high yield. Conversely, an acyclic aliphatic hydrazide specifically bearing a beta heteroatom (N-carbobenzyloxyglycine hydrazide) produced the expected 4-aminotriazole adduct in high yield. This therefore appears to be a general phenomenon which provides a useful synthetic entry to several new unsymmetrically substituted 4-amino-1,2,4-triazole derivatives.     

Reactions of α-mercaptocarboxylic acid hydrazides with triethyl orthoesters: synthesis of 1,3,4-thiadiazin-5(6H)-ones and 1,3,4-oxadiazoles

Reactions of α-mercapto-β-phenylpropionic and α-mercaptophenylacetic acid hydrazides with triethyl orthoesters were conducted under N₂ in glacial acetic acid and resulted in the formation of two groups of products, derivatives of 1,3,4-thiadiazin-5(6H)-ones and 2-(1-mercaptomethyl)-1,3,4-oxadiazoles. When conducting the same transformations on α-mercaptophenylacetic acid hydrazide in the presence of air, two different products from the 1,3,4-oxadiazole family, the appropriate bis(1,3,4-oxadiazol-2-yl-phenylmethyl) disulfides and 2-benzyl-1,3,4-oxadiazoles, were formed with the liberation of free sulfur. The oxygenated bis(1,3,4-oxadiazol-2-yl-phenylmethyl) disulfides were reduced to the corresponding 2-(1-mercaptomethyl)-1,3,4-oxadiazoles with the use of zinc powder under mild conditions.     

Synthesis and absorption spectra of 3,5-diaryl-1,2,4-triazoles

1,2,4-Triazoles with symmetrical tolyl substituents were obtained from the corresponding 1,3,4-oxadiazoles by reaction with formamide and subsequent hydrolysis of the resulting formyl derivatives; 1,2,4-triazoles with unsymmetrical substituents were obtained from iminoesters and hydrazides of acids. A set of bands of the triazole ring at 1470–1480, 1390, 1270–1290, 1140–1150, and 725–750 cm^–1 and of NH vibrations at 2400–3200, 1580–1620, and 830–900 cm^–1 are characteristic for the IR spectra of these triazoles. The UV spectra of the triazoles are characterized by phenyl ring absorption at about 200 nm and a band of electron transitions between the phenyl and triazole rings at 230–290 nm.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1682–1685, December, 1977.     

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.     

2-Halogenoethyl and 2-halogenoethylthiol esters of furan series carboxylic acids

The corresponding 2-chloroethyl (2-chloroethylthiol) esters are synthesized by the action of ethylene chlorohydrin (chloroethylmercaptan) on the acid chlorides of 5-nitrofuran carboxylic acid and 3-(5-nitrofuryl-2)acrylic acid. The acid chlorides of benzoic, furan carboxylic, and 3-(furyl-2)-acryllc acids react with ethylene sulfide, to give 2-chloroethyl esters of those acids. Ethylene oxide does not react with the acid chlorides of benzoic acid and furan series carboxylic acids either at room temperature or on heating at 50° for 1 hour.