Selective synthesis of novel 2-imino-1,3-selenazolidin-4-ones and 2-amino-1,3,4-selenadiazin-5-ones from isoselenocyanates

An efficient and regioselective synthesis of 2-imino-1,3-selenazolidin-4-ones and 2-amino-1,3,4-selenadiazin-5-ones was achieved via one-pot reaction of isoselenocyanates, hydrazines, and ethyl chloroacetate or chloroacetyl chloride, respectively. Plausible mechanisms for these transformations were given.     

Efficient one-pot synthesis of substituted 2-amino-1,3,4-oxadiazoles

A convenient one-pot method for the preparation of substituted 2-amino-1,3,4-oxadiazoles has been developed. The method is a significant improvement over previously reported syntheses. Reaction of carboxylic acids with thiosemicarbazides afforded the corresponding oxadiazoles in moderate to good yields. In general, the products precipitated from the reaction mixture, and were collected by filtration. In most of the cases, no chromatographic separations were required. To explore the scope and limitations of this reaction, various aliphatic, aromatic, and heteroaromatic carboxylic acids were reacted with different substituted thiosemicarbazides. The influence of R¹ and R² substituents on the reaction yield and additional results demonstrating the versatility of this method are presented.     

Synthesis of sugar-derived isoselenocyanates, selenoureas, and selenazoles

Aryl, alkyl, and sugar-derived isoselenocyanates were prepared by a one-pot procedure starting from the corresponding formamides, using triphosgene as a dehydrating agent, triethylamine, and black selenium powder. The preparation of sugar selenoureas by coupling of O-protected sugar-derived isoselenocyanates with different amines, and by coupling of unprotected glycopyranosyl amines with phenyl isoselenocyanate was also accomplished. The synthesis of a glucopyranos-2-yl-selenazole starting from O-protected 2-amino-2-deoxy-d-glucose by coupling with benzoyl isoselenocyanate, Se-alkylation with phenacyl bromide, and acid-catalyzed dehydration is also reported. Unprotected N-(β-d-glucopyranosyl)-N′-phenylselenourea was transformed into a 1,2-trans-fused bicyclic isourea upon treatment with aqueous hydrogen peroxide; the same isourea was prepared by a one-pot three-step procedure from β-d-glycopyranosylamine by thiophosgenation, coupling with aniline, and HgO-mediated desulfurization.     

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.     

Efficient one-pot preparation of 5-substituted-2-amino-1,3,4-oxadiazoles using resin-bound reagents

A robust one-pot solution-phase synthesis of 2-amino-1,3,4-oxadiazoles directly from acylhydrazines and isothiocyanates is described. Commercially-available polymer-supported reagents help facilitate both cyclization and purification. This convenient method benefits from its broad applicability, ease and safety of reagent handling, simple product isolation, and the ability to perform multiple reactions in parallel fashion without need for purification. The details and scope of this reaction strategy are presented herein.     

Selenium-containing heterocycles from isoselenocyanates: synthesis of 2-methylidene-1,3-selenazolidine derivatives

A convenient and unequivocal synthesis of the title compounds from isoselenocyanates, malononitrile or 2-cyanoacetate, and 1,2-dibromoethane or α-halogenated carboxylic acid derivatives is reported. The proposed reaction mechanism involves in situ cyclization of different halogenated compounds with an intermediate keten-N,Se-acetal, generated by the base promoted nucleophilic addition of the acidic cyanomethylenes to aliphatic and aromatic isoselenocyanates. Chemical and spectroscopic evidence for the structures of the new compounds is presented.     

Alum (KAl(SO4)2 · 12H2O): An Efficient and Inexpensive Catalyst for the One-pot Synthesis of 1,3,4-Oxadiazoles under Solvent-Free Conditions

Summary. 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.     

Synthesis of 5-amino-2-selenoxo-1,3-imidazole-4-carboselenoamides by the reaction of isoselenocyanates with aminoacetonitriles

Reaction of isoselenocyanates with aminoacetonitriles afforded 4-amino-2-selenoxo-1,3-imidazole-2-selenones, whereas reaction with aminopropionitriles led to selenoureas. We confirmed that it is easy to distinguish between selenoamides and selenoureas by comparison of their chemical shift differences in the ⁷⁷Se NMR spectra.     

Efficient phosphonium-mediated synthesis of 2-amino-1,3,4-oxadiazoles

We present an efficient, room temperature procedure for the preparation of 2-amino-1,3,4-oxadiazoles. Oxadiazol-2-ones can be activated for SNAr substitution using phosphonium reagents (e.g., BOP). This approach provides convenient access to N,N-disubstituted 2-amino-1,3,4-oxadiazoles, which are difficult to prepare using existing synthetic strategies.     

Efficient synthesis of 1,3,4-oxadiazoles promoted by NH4Cl

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.     

Synthesis of 2-amino-5-substituted-1,3,4-oxadiazoles using 1,3-dibromo-5,5-dimethylhydantoin as oxidant

A scalable synthesis of 5-substituted-2-amino-1,3,4-oxadiazoles via oxidation of a thiosemicarbazide precursor is described. The thiosemicarbazide intermediates are easily accessed from the corresponding acid chlorides. Oxidative cyclization using 1,3-dibromo-5,5-dimethylhydantoin as the primary oxidant, in the presence of potassium iodide, gives a variety of oxadiazoles in good yields. This methodology utilizes a commercially inexpensive and easily handled oxidant.     

2-芳基-5-苄氧苯基-1,3,4-噁二唑类化合物的合成

由苄氧基苯甲酰肼与各种芳酰氯反应制得N-取代苯甲酰基-4-苄氧苯酰肼(2),2在三氯氧磷存在下发生脱水闭环反应,合成了一系列2-芳基-5-苄氧苯基-1,3,4-噁二唑类化合物,其结构经1H NMR,IR,MS和元素分析表征。     

2-对氯苯氧基-5-芳基-1,3,4-噁二唑的合成

对氯苯氧乙酸乙酯与水合肼反应制得对甲基苯氧乙酰肼（2）;以碳酸钠作缚酸剂,2与卤代苯甲酰氯反应合成了N、N＇-二酰基肼（3）;在POCl3作用下,3脱水环化得2-对氯苯氧基-5-芳基-1,3,4-噁二唑,其结构经1^H NMR,IR,MS和元素分析表征,并对其裂解途径进行了探讨。     

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.     

2-芳氧基-5-苯基-1,3,4-恶二唑类化合物的合成

通过芳氧基负离子在2-甲磺酰基-5-1,3,4-恶二唑上的亲核取代反应制得2-芳氧基-5-苯基-1,3,4-恶二唑.所有化合物的结构经元素分析,IR, ^1H NMR和MS确证.这些化合物表现出一定的抑制枯草芽孢杆菌繁殖的活性.     

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.     

Superior reactivity of thiosemicarbazides in the synthesis of 2-amino-1,3,4-oxadiazoles

A facile and general protocol for the preparation of 2-amino-1,3,4-oxadiazoles is reported. This method relies on a tosyl chloride/pyridine-mediated cyclization of a thiosemicarbazide, which is readily prepared by acylation of a given hydrazide with the appropriate isothiocyanate. Cyclization of the thiosemicarbazide consistently outperforms the analogous semicarbazide cyclization under these conditions, for 18 distinct examples. Utilizing this protocol, we have prepared 5-alkyl- and 5-aryl-2-amino-1,3,4-oxadiazoles in 78-99% yield.     

Synthesis of steroidal extranucleo 1,3,4-oxadiazoles

Cholest-5en-3β-ol 1 , 3,3-ethylenedioxy-androst-4-en-17β-ol 2 and 17,17-ethylenedioxy-1,3,5(10)-estratrien-3β-ol 3 were converted into ethyl ester 1a, 2a and 3a by reaction with ethyl chloroacetate in the presence of potassium. The ethyl esters 1a, 2a and 3a on reaction with hydrazine gave hydrazides 1b, 2b and 3b , which on reaction with cyanogen bromide afforded 1,3,4-oxadiazoles 1c, 2c and 3c .