- Electrochemical Synthesis of 2,5-Disubstituted 1,3,4-Oxadiazoles from α-Keto Acids and Acylhydrazines Under Mild Conditions
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1,3,4-Oxadiazoles are a kind of useful heterocycles which can be frequently found in materials and bioactive molecules. In this study, intermolecular electrochemical cyclization between α-keto acids and acylhydrazines has been developed for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles with the yield up to 91 %. This transformation can be run under mild reaction conditions in the absence of external oxidant, base and transition metal catalyst. Both symmetrical and unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles could be prepared according to the careful choice of the substrate combination. Gram scale synthesis also illustrates the potential application of this protocol in large preparation.
- Lu, Fangling,Gong, Fengping,Li, Liangsen,Zhang, Kan,Li, Zhen,Zhang, Xinwei,Yin, Ying,Wang, Ying,Gao, Ziwei,Zhang, Heng,Lei, Aiwen
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supporting information
p. 3257 - 3260
(2020/05/25)
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- A convergent synthesis of 1,3,4-oxadiazoles from acyl hydrazides under semiaqueous conditions
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The 1,3,4-oxadiazole is an aromatic heterocycle valued for its low-lipophilicity in drug development. Substituents at the 2- and/or 5-positions can modulate the heterocycle's electronic and hydrogen bond-accepting capability, while exploiting its use as a carbonyl bioisostere. A new approach to 1,3,4-oxadiazoles is described wherein α-bromo nitroalkanes are coupled to acyl hydrazides to deliver the 2,5-disubstituted oxadiazole directly, avoiding a 1,2-diacyl hydrazide intermediate. Access to new building blocks of oxadiazole-substituted secondary amines is improved by leveraging chiral α-bromo nitroalkane or amino acid hydrazide substrates. The non-dehydrative conditions for oxadiazole synthesis are particularly notable, in contrast to alternatives reliant on highly oxophilic reagents to effect cyclization of unsymmetrical 1,2-diacyl hydrazides. The mild conditions are punctuated by the straightforward removal of co-products by a standard aqueous wash.
- Tokumaru, Kazuyuki,Johnston, Jeffrey N.
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p. 3187 - 3191
(2017/04/04)
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- Efficient synthesis of 1,3,4-oxadiazoles promoted by NH4Cl
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An efficient and inexpensive approach to the synthesis of 2-substituted and 2,5-disubstituted 1,3,4-oxadiazoles from arylhydrazides and orthoesters is reported using catalytic NH4Cl. The conditions are mild, and thus, compatible with a variety of functional groups. The optimized reaction is performed using 30 mol % of NH4Cl in 100% EtOH and is generally complete within 1 h for non-aromatic orthoesters and 2-10 h for aromatic orthoesters. The reaction permits both electron-releasing and electron-withdrawing groups on the arylhydrazide substrate. Most products are formed in high yields and require only minimal purification. Compared with earlier reports, the current reactions proceed in shorter time and require less of the orthoester.
- Gnanasekaran, Krishna Kumar,Nammalwar, Baskar,Murie, Maeghan,Bunce, Richard A.
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supporting information
p. 6776 - 6778
(2015/01/09)
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- One-pot synthesis of 2,5-disubstituted-1,3,4-oxadiazoles based on the reaction of N,N-dimethyl amides with acid hydrazides
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Convenient and efficient one pot method for the synthesis of 2,5-disubstituted-1,3,4-oxadiazoles based on the reaction of N,N-dimethyl amides with acid hydrazides has been developed. The methodology is applied to a wide range of difference aryl hydrazide and difference N,N-dimethyl amides to 2,5-disubstituted-1,3,4-oxadiazoles yield the in good to excellent yields. It will be possible wide useful application in synthesis. Synopsis Convenient and efficient one pot method for the synthesis of 2,5-disubstituted-1,3,4- oxadiazoles based on the reaction of N,N-dimethyl amides with acid hydrazides has been developed. The methodology is applied to a wide range of difference aryl hydrazide and difference N,N-dimethyl amides to 2,5-disubstituted- 1,3,4-oxadiazoles yield the in good to excellent yields. It will be possible wide useful application in synthesis. Copyright
- Li, Qiang,Tao, Yi,Xu, Dongfang,Zhang, Haobing,Duan, Liping
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p. 665 - 670
(2014/06/24)
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- High-temperature continuous flow synthesis of 1,3,4-oxadiazoles via N-acylation of 5-substituted tetrazoles
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Applying continuous flow processing in a high-temperature/high-pressure regime (200-220 °C, 11-14 bar) 2,5-disubstituted-1,3,4-oxadiazoles are prepared in high yields within 5-10 min residence time by treatment of 5-substituted-1H-tetrazoles with anhydrides or acid chlorides as electrophiles (Huisgen reaction).
- Reichart, Benedikt,Kappe, C. Oliver
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supporting information; experimental part
p. 952 - 955
(2012/03/11)
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- Greener and rapid access to bio-active heterocycles: one-pot solvent-free synthesis of 1,3,4-oxadiazoles and 1,3,4-thiadiazoles
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A novel one-pot solvent-free synthesis of 1,3,4-oxadiazoles and 1,3,4-thiadiazoles by condensation of acid hydrazide and triethyl orthoalkanates under microwave irradiations is reported. This green protocol was catalyzed efficiently by solid supported NafionNR50 and phosphorus pentasulfide in alumina (P4S10/Al2O3) with excellent yields.
- Polshettiwar, Vivek,Varma, Rajender S.
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p. 879 - 883
(2008/09/17)
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- Silica sulfuric acid: An efficient and versatile acidic catalyst for the rapid and ecofriendly synthesis of 1,3,4-oxadiazoles at ambient temperature
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A rapid and green synthesis of 2,5-disubstituted 1,3,4-oxadiazoles is reported. The title compounds were prepared by the reaction of different acyl hydrazides and orthoesters in the presence of silica sulfuric acid under solvent-free conditions. In this new process, reactions were run at ambient temperature and completed in a short period of time with high yields. Copyright Taylor & Francis Group, LLC.
- Dabiri, Minoo,Salehi, Peyman,Baghbanzadeh, Mostafa,Zolfigol, Mohammad Ali,Bahramnejad, Mahboobeh
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p. 1201 - 1209
(2008/02/01)
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- Alum (KAl(SO4)2 ? 12H2O): An efficient and inexpensive catalyst for the one-pot synthesis of 1,3,4-oxadiazoles under solvent-free conditions
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Alum (KAl(SO4)2 ? 12H2O) catalyzed the efficient synthesis of mono- and disubstituted 1,3,4-oxadiazoles by the condensation of acyl hydrazides with orthoesters under solvent-free conditions at 100°C. This methodology offers significant improvements for the synthesis of oxadiazoles with regard to the yield of products, simplicity in operation, inexpensive reagents, and green aspects by avoiding toxic catalysts and solvents.
- Dabiri, Minoo,Salehi, Peyman,Baghbanzadeh, Mostafa,Bahramnejad, Mahboobeh
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p. 1253 - 1255
(2008/03/28)
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- A facile procedure for the one-pot synthesis of unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles
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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.
- Dabiri, Minoo,Salehi, Peyman,Baghbanzadeh, Mostafa,Bahramnejad, Mahboobeh
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p. 6983 - 6986
(2007/10/03)
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- Facile synthesis of symmetric and unsymmetric 1,3,4-oxadiazoles using 2-acyl(or aroyl)pyridazin-3-ones
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Symmetric and unsymmetric 1,3,4-oxadiazoles were synthesized in situ from hydrazine hydrate and the corresponding 2-acyl-4,5-dichloropyridazin-3-ones as acylating agents in polyphosphoric acid or BF3·OEt2 in excellent yields.
- Park, Yong-Dae,Kim, Jeum-Jong,Chung, Hyun-A,Kweon, Deok-Heon,Cho, Su-Dong,Lee, Sang-Gyeong,Yoon, Yong-Jin
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p. 560 - 564
(2007/10/03)
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- A new synthesis of 1,3,4-oxadiazoles. Cyclization of N,N'- diacylhydrazines catalyzed by palladium(0)
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Several 1,3,4-oxadiazoles were synthetized by cyclization of N,N'- diacylhydrazines catalyzed by palladium(0). Water formed during the reaction is responsible for the hydrolysis of the products. To avoid it, we introduced benzoic anhydride into the medium and obtained an increased yield of oxadiazoles.
- Lutun, Stephane,Hasiak, Bruno,Couturier, Daniel
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p. 111 - 116
(2007/10/03)
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