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.     

Syntheses and insecticidal activities of novel 2,5-disubstituted 1,3,4-oxadiazoles

Nine novel symmetrical and asymmetrical 2,5-disubstituted 1,3,4-oxadiazoles have been synthesized by a facile and mild method with high yield. Meantime, it was found that the fluorine was easy substituted by hydrazine in polyhalogen-substituted aroyl hydrazine. The preliminary bioassay tests show that two of the compounds (D5 and D6) exhibited a significant insecticidal activity (LC₅₀=116.02 and 70.93 mg l⁻¹) on armyworm, Leucania separata Walker. Using the Drug Discovery Workbench (DDW) (Cerius²), structure-activities relationship was studied.     

One-pot synthesis of 1,3,4-thiadiazoles using Vilsmeier reagent as a versatile cyclodehydration agent

A simple and efficient synthetic method for the one-pot synthesis of 1,3,4-thiadiazoles utilizing Vilsmeier reagent was developed. In this method carboxylic acids and hydrazine were converted to 1,3,4-thiadiazoles in the presence of Vilsmeier reagent and Lawesson's reagent. The influence of the thionation reagent, solvent, temperature and time, in this reaction was discussed. The developed methodology for 1,3,4-thiadiazole synthesis has the advantage of simplicity, ambient reaction conditions, easy purification and good to excellent yield of products.     

Synthesis and evaluation of in vitro antibacterial activity of novel 2,5-disubstituted-1,3,4-thiadiazoles from fatty acids

A series of new 1-(alkenoyl/hydroxyalkenoyl)-4-benzoyl-thiosemicarbazides 2a-d and 2-benzamide-5-alkenyl/hydroxyalk-enyl-1,3,4-thiadiazoles 3a-d were synthesized from fatty acid hydrazides. Structure of all these compounds was confirmed by IR, 1H NMR, 13C NMR, mass spectra and elemental analysis. The bioassay results indicate that some compounds 2,c, 2d, 3c and 3d have good antibacterial activity.     

Synthesis and evaluation of in vitro antibacterial activity of novel 2,5-disubstituted-1,3,4-thiadiazoles from fatty acids

A series of new 1-（alkenoyl/hydroxyalkenoyl）-4-benzoyl-thiosemicarbazides 2a-d and 2-benzamide-5-alkenyl/hydroxyalk- enyl-1,3,4-thiadiazoles 3a-d were synthesized from fatty acid hydrazides. Structure of all these compounds was confirmed by IR, IH NMR, Sac NMR, mass spectra and elemental analysis. The bioassay results indicate that some compounds 2e, 2d, 3e and 3d have good antibacterial activity.     

Synthesis and biological evaluation of newer analogues of 2,5-disubstituted 1,3,4-oxadiazole containing pyrazole moiety as antimicrobial agents

A series of 2,5-disubstituted-1,3,4-oxadiazole derivatives bearing pyrazole moiety were synthesized by reacting various substituted pyrazole-4-carboxylic acids with different hydrazides in POCl₃. All the synthesized compounds (4a–n) were characterized by IR, NMR, mass spectra and elemental analyses. Synthesized 1,3,4-oxadiazole derivatives were screened for their antibacterial activity against three different strains, namely Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, while antifungal activity was determined against three different strains Aspergillus flavus, Chrysosporium keratinophilum and Candida albicans. The investigation of antimicrobial screening revealed that compounds 4i and 4j exhibited excellent activity when compared with the standard drugs.     

Versatile strategies for the solid phase synthesis of small heterocyclic scaffolds: [1,3,4]-thiadiazoles and [1,3,4]-oxadiazoles

New robust protocols for the solid phase synthesis of 5-alkylthio-, 5-alkyl/aryl-, and 5-acylamino-2-alkylamino-[1,3,4]-thiadiazoles are described based on a common resin bound thiosemicarbazide. A protocol for the solid phase synthesis of 2-alkyl/aryl-amino-5-alkylamino-[1,3,4]-oxadiazoles from a resin bound semicarbazide is likewise reported. The protocols have been verified by the preparation of four small libraries that all gave products in good to excellent yields and purity.     

Synthesis and biological evaluation of some novel thiadiazole-benzofuran hybrids as potential antitumor agents

Two series of novel 1,3,4-thiadiazole-benzofuran and 1,3,4-thiadiazole-furochromene derivatives were synthesized through heterocyclization of alkyl 2-(1-(6-hydroxy-4,7-dimethoxybenzofuran-5-yl)ethylidene)hydrazine-1-carbodithioate 3a–f and 2-(1-(5-methoxy-8-methyl-2,6-dioxo-2,6-dihydropyrano[3,2-g]chromen-3-yl)ethylidene)hydrazinecarbothioamide 9a,b with various hydrazonoyl halides, respectively. The structure of the newly synthesized products was elucidated through elemental analysis, spectral data and alternative routes whenever possible. Ten new compounds were evaluated for their anticancer activity against the human breast carcinoma (MCF-7) cell lines in comparison with reference doxorubicin using MTT assay. The results showed that some new compounds have promising anticancer activity.     

Microwave assisted syntheses of 2,5-disubstituted 1,3,4-oxadiazoles

2,5-Disubstituted 1,3,4-oxadiazoles have been synthesized by oxidation of 1-aroyl-2-arylidene hydrazines with potassium permanganate on the surface of a solid mineral support as well as in mixtures of acetone and water under microwave irradiation.     

One-pot synthesis, antibacterial and antifungal activities of novel 2,5-disubstituted-1,3,4-oxadiazoles

A series of novel 2,5-disubstituted-1,3,4-oxadiazoles have been synthesized from long-chain alkanoic and alkenoic acids. The structures of these compounds have been elucidated by elemental and spectral （IR, ^1H NMR, ^13C NMR, MS） analysis. Furthermore, compounds were screened for in vitro antibacterial activity against the representative panel of two Gram-positive and two Gram- negative bacteria. All the synthesized compounds were also tested for their inhibitory action against five strains of fungus. The various compounds show potent inhibitory action against test organisms. 2007 Abdul Rauf. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

A facile procedure for the one-pot synthesis of unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles

Unsymmetrically 2,5-disubstituted 1,3,4-oxadiazoles were efficiently synthesized from the cyclization-oxidation reaction of acyl hydrazones. Also, the synthesis of the title compounds was achieved by the condensation of acyl hydrazides and aromatic aldehydes in the presence of ceric ammonium nitrate in dichloromethane.     

Design,synthesis and screening of some novel benzoxazole based 1,3,4-oxadiazoles as potential antimicrobial agents

A series of novel 2-(5-substituted-[1,3,4]oxadiazol-2-yl)-benzoxazoles (7a–h) were synthesized in good yields in two different directions by involving benzoxazole-2-carboxylic acid (1) as raw material and benzoxazole-2-carbonyl chloride (2), benzoxazole-2-carboxylic acid methyl ester (3), benzoxazole-2-carboxylic acid hydrazide (4), benzoxazole-2-carboxylic acid N′-acetyl hydrazide (5a–d) and benzoxazole-2-carboxylic acid-ethylidene-hydrazides (6a–d) as reactive intermediates. The chemical structures of all the synthesized compounds were elucidated by their IR, ¹H NMR and ¹³C NMR and mass spectral data. Further, the target compounds were screened for their antimicrobial activity against various Gram-positive and Gram-negative bacteria.     

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.     

Convenient preparation of unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles promoted by Dess-Martin reagent

2,5-Disubstituted 1,3,4-oxadiazoles have been conveniently prepared by oxidative cyclization of N-acyl-N′-aryliden-hydrazines promoted by an excess of Dess-Martin periodinane under mild conditions (23 examples, up to 92% isolated yields).     

Solvent-Free Green Synthesis of Azines and Their Conversion to 2,5-Disubstituted-1,3,4-thiadiazoles

A solvent-free, clean, and efficient method has been developed for the synthesis of 2,5-disubstituted-1,3,4-thiadiazoles via azines. This approach exploits the synthetic potential of clean reactions and offers many advantages such as excellent product yields, easy isolation of products, and ecofriendly benign reaction conditions. The newly synthesized compounds were analyzed by infrared, ¹H NMR, ¹³C NMR, and elemental analysis.     

2－芳酰氨基－5－（5－苯基－2H－四唑2－甲基）－1，3，4－噻二唑类化合物的合成

在浓硫酸作用下，由５－（５－苯基－２Ｈ四唑－２－乙酰基）－４－芳酰氨基硫脲１ａ～ｎ制得了一系列新的２－芳酰氨基－５－（５－苯基－２Ｈ－四唑－２－甲基）－１，３，４－噻二唑化合物（２ａ～ｎ）。所有化合物的结构均经元素分析、ＭＳ分析，部分代表化合物经ＩＲ、￣ＨＮＭＲ分析确证；初步观察了２ａ～ｎ在１％浓度下对大肠杆菌（Ｇ￣－）的抑制作用，发现２ｄ，２ｅ，２ｆ，２ｎ显示出较强的活性。     

A new synthesis of symmetrical 2,5-diaryl-1,3,4-thiadiazoles

Treatment of aromatic aldehydes with sulfur and hydrazine hydrate in the ratio 1:2:3, respectively, under the Willgerodt conditions affords the title compounds in excellent yields and in a good state of purity. Under the same conditions 2-chloro and 2,6-dichlorobenzaldehyde yield 3H-1,2-benzodithiole-3-thione and bis-(2,6-dichlorobenzyl)tetrasulfide, respectively.     

Novel and Efficient Cyclization Procedure for the Synthesis of 2,5-Disubstituted-1,3,4-thiadiazoles Without Using Any Ring-Closing Reagents

A novel method for the synthesis of 2,5-disubstituted-1,3,4-thiadiazoles via direct ring closure of 1,6-disubstituted-2,5-dithioureas in dimethylformanide without using any ring-closing reagents has been accidentally discovered. Repeated and extended experiments confirmed that this is a very simple and efficient way to synthesize these kinds of fine chemicals. A series of novel 2,5-disubstituted-1,3,4-thiadiazoles have been synthesized via this method in good yields.     

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.     

Synthesis of N-pyrimidin[1,3,4]oxadiazoles and N-pyrimidin[1,3,4]-thiadiazoles from 1,3,4-oxadiazol-2-amines and 1,3,4-thiadiazol-2-amines via Pd-catalyzed heteroarylamination

An efficient and practical procedure was developed to prepare various N-pyrimidin[1,3,4]oxadiazole and thiadiazole scaffolds using a Buchwald-type coupling. The products of this reaction are otherwise difficult to access and could be used as building blocks in drug design.