3,4‐Di‐2‐pyridyl‐1,2,5‐oxadiazole and its perchlorate salt

In 3,4‐di‐2‐pyridyl‐1,2,5‐oxadiazole (dpo), C₁₂H₈N₄O, each mol­ecule resides on a twofold axis and inter­acts with eight neighbours via four C—H⋯N and four C—H⋯O inter­actions to generate a three‐dimensional hydrogen‐bonded architecture. In the perchlorate analogue, 2‐[3‐(2‐pyrid­yl)‐1,2,5‐oxadiazol‐4‐yl]pyridinium perchlorate, C₁₂H₉N₄O⁺·ClO₄⁻ or [Hdpo]ClO₄, the [Hdpo]⁺ cation is bisected by a crystallographic mirror plane, and the additional H atom in the cation is shared by the two pyridyl N atoms to form a symmetrical intra­molecular N⋯H⋯N hydrogen bond. The cations and perchlorate anions are linked through C—H⋯O hydrogen bonds and π–π stacking inter­actions to form one‐dimensional tubes along the b‐axis direction.     

Heterocyclic ring cleavage upon collision‐induced dissociation of deprotonated 3‐hydroxy‐1,2,5‐oxadiazoles (3‐hydroxyfurazans)

A series of 4‐substituted 3‐hydroxyfurazans were subjected to electrospray ionization tandem mass spectrometry. At low collision energy, oxyisocyanate ([O=C=N–O]^?, m/z 58) was formed as the predominant product ion from each deprotonated 3‐hydroxyfurazan, indicating cleavage of the heterocyclic ring. The facile energetics of this characteristic fragmentation process was confirmed by density functional computations.     

A `tetrameric' 3,4‐di‐p‐tolyl‐1,2,5‐oxadiborole derivative

In the title compound, 1,1,6a,7,9a,10‐hexa­chloro‐2,3,5,6,8,9,11,12‐octa‐p‐tolyl‐1,6a,9a,12a‐tetraborata‐3a,4a,7,10‐tetrabora‐4a¹,6b,9b,12b‐tetraoxonia‐4‐oxatetra­cyclo­penta­[1,2‐a:2,1,5‐de:1,2‐g:1,2‐i]­naphthalene di­chloro­methane pentasolvate, C₆₄H₅₆B₈Cl₆O₅·5CH₂Cl₂, two condensed oxadiborole rings are attached to two further oxadiborole rings in a type of donor–acceptor bonding, thus forming a ten‐membered alternating (B—O)₅ naphthalene‐like arrangement as the central building block.     

Facile synthesis of new imidazoles from direct reaction of 2,3‐diamino‐1,4‐naphthoquinone with aldehydes

New imidazoles were easily prepared from 2,3‐diamino‐1,4‐naphthoquinone and stoichiometric quantities of the appropriate aldehydes in dimethyl sulfoxide as a solvent. The reaction proceeded for few hours. The procedure can be generalized to different classes of aldehydes. 2‐Methyl‐1H‐naphtho[2,3‐d]imidazole‐4,9‐dione was also obtained in good yield during refluxing of 2,3‐diaminonaphthoquinone in acetic acid. The structure of the newly synthesized imidazoles was extensively investigated using NMR experiments. J. Heterocyclic Chem., (2011).     

A New Route to Synthesis of 3,6‐Diaryl‐1,2,4‐triazolo[3,4‐b]1,3,4‐oxadiazoles

Five new 3,6‐diaryl‐1,2,4‐triazolo[3,4‐b]1,3,4‐oxadiazole derivatives were synthesized by 9 steps from aromatic acids and evaluated for their activities of anticancer and antibacteria. The structures of all new compounds synthesized were elucidated by MS, IR, ¹HNMR and HRMS.     

A Re‐Examination of the Reaction of 3,4‐Diamino[1,2,5]oxadiazole with Glyoxal

Reaction coordinate mapping was used to study the reaction of 3,4‐diamino[1,2,5]oxadiazole (3,4‐diaminofurazan) and 3,4‐diamino[1,2,5]thiadiazole with glyoxal. The thiadiazole was known to give a good yield of [1,2,5]thiadiazolo[3,4‐b]pyrazine, whereas the oxadiazole had not yielded, until now, [1,2,5]oxadiazolo[3,4‐b]pyrazine (or furazano[2,3‐b]pyrazine). The calculations suggested that the diols, 5,6‐dihydroxy‐4,5,6,7‐tetrahydro[1,2,5]oxadiazolo[3,4‐b]pyrazine and 5,6‐dihydroxy‐4,5,6,7‐tetrahydro[1,2,5]thiadiazolo[3,4‐b]pyrazine should be stable intermediates, and once formed, should provide a pathway to the target compounds via two dehydration steps, under forcing conditions. With this information in mind, the reactions of 3,4‐diamino[1,2,5]oxadiazole with glyoxal and pyruvic aldehyde were re‐examined. The reaction of 3,4‐diamino[1,2,5]oxadiazole with glyoxal and pyruvic aldehyde produced, under slightly basic conditions, a near quantitative yield of the expected initial products, 5,6‐dihydroxy‐4,5,6,7‐tetrahydro[1,2,5]oxadiazolo[3,4‐b]pyrazine and the 5‐methyl analog, respectively. The diols were easily isolated by lyophilizing the aqueous reaction mixture. The diols were pyrolized on silica gel at 160°C to give the desired [1,2,5]oxadiazolo[3,4‐b]pyrazine and the 5‐methyl analog. Both compounds were easily reduced to the corresponding 4,5,6,7‐tetrahydro‐derivative using sodium borohydride in THF/methanol. The [1,2,5]oxadiazolo[3,4‐b]pyrazine also displayed other interesting chemistry.     

Benzo[1,2‐c:3,4‐c']bis[1,2,5]selenadiazole, [1,2,5]selenadiazolo‐[3,4‐e]‐2,1,3‐benzothiadiazole,furazanobenzo‐2,1,3‐thiadiazole,furazanobenzo‐2,1,3‐selenadiazole and related heterocyclic systems

The first synthesis of benzo[1,2‐c:3,4‐c']bis[1,2,5]selenadiazole has been developed starting from commercially available 4‐nitrobenzo‐2,1,3‐selenadiazole. Improved syntheses of the related heterocycles [1,2,5]selenadiazolo[3,4‐e]‐2,1,3‐benzothiadiazole, furazanobenzo‐2,1,3‐thiadiazole and furazanobenzo‐2,1,3‐selenadiazole are also reported.     

Facile routes for the preparation of 3,4‐disubstituted 1,3‐oxazolidines and 1,2,5‐trisubstituted imidazolidin‐4‐ones

Facile, alternative synthetic routes to 6 , (R)‐6 , and (S)‐6 ‐3‐benzyl‐N‐(2,6‐dimethylphenyl)‐1,3‐oxazolidine‐4‐carboxamides ( 6 ), a chiral oxazolidine derivative of tocainide, are reported. The synthetic routes described herein also afforded 11 ‐, (R)‐11 ‐, and 12 , which present the imidazolidin‐4‐one core and belong to a class of compounds interesting for their biological activities. All the final compounds and intermediates were fully characterized. Enantiomeric excesses of homochiral 6 and 11 were determined by capillary electrophoresis analysis using 2‐hydroxypropyl‐β‐cyclodextrin or highly sulfated γ‐cyclodextrin as chiral selectors. J. Heterocyclic Chem., (2010)     

TiO2‐Nanoparticles Catalyzed Synthesis of New Trifluoromethyl‐4,5‐dihydro‐1,2,4‐oxadiazoles and Trifluoromethyl‐1,2,4‐oxadiazoles

Synthesis of a new series of trifluoromethyl‐4,5‐dihydro‐1,2,4‐oxadiazoles and trifluoromethyl‐1,2,4‐oxadiazoles have been described by utilizing the reactions between amidoximes and trifluoroacetimidoyl chlorides. Trifluoromethyl‐4,5‐dihydro‐1,2,4‐oxadiazoles have been synthesized under mild conditions such as Na₂CO₃, THF‐H₂O, and titanium dioxide nanoparticles as catalyst in good to excellent yields. Also, trifluoromethyl‐1,2,4‐oxadiazoles have been synthesized directly from reaction of amidoximes and trifluoroacetimidoyl chlorides in a one‐pot manner in present of NaH, THF, and titanium dioxide nanoparticle as catalyst.     

Determination of Selenium with a Poly(1,8‐diamino‐naphthalene)‐Modified Electrode

The performance of a poly(1,8‐diaminonaphthalene)‐modified electrode for the determination of the Se(IV) ion in an aqueous medium was investigated with anodic stripping voltammetry without the pretreating of the sample. The experimental parameters for the analysis of Se(IV) were optimized and the characteristics of this polymer‐modified electrode were investigated by using cyclic voltammetry. The Se(IV) ions were chemically deposited onto the surface of the pDAN‐Au electrode in an acidic medium. The detection limit employing the anodic stripping differential pulse voltammetry was 9.0×10^?9 M for Se(IV) with 4.4 % of RSD. Satisfactory result for the determination of Se(IV) was acquired employing a certified standard urine reference material, SRM's 2670 (trace element in urine) with 4.1 ppb of SD.     

Photoinduced molecular rearrangements. Some comments on the ring‐photoisomerization of 1,2,4‐oxadiazoles into 1,3,4‐oxadiazoles

The ring‐photoisomerization of 3‐amino‐ and 3‐methylamino‐5‐phenyl‐1,2,4‐oxadiazoles into the corresponding 2‐amino‐ and 2‐methylamino‐5‐phenyl‐1,3,4‐oxadiazoles has been reinvestigated by examining the effect of a base on the photoreaction. On irradiating at λ = 254 nm in methanol, yields of the ring‐photoisomers were found to be significantly enhanced by the addition of triethylamine (TEA) in the photoreaction medium. By contrast, irradiation of the 3‐amino‐5‐phenyloxadiazole in acetonitrile containing TEA gave an almost complete photoreduction into benzoylguanidine, while few percent of the ring photoisomer were detected. Furthermore, the pyrene‐sensitized photolysis of 3‐amino‐5‐phenyloxadiazole in acetonitrile containing triethylamine also gave benzoylguanidine but no traces of the ring photoisomer.     

Preparation and physical properties of poly(4,4′‐diamino‐3′‐carbamoylbenzanilide terephthalamide) and poly(4,4′‐diamino‐3′‐carbamoylbenzanilide isophthalamide) films

To prepare thermally stable and high‐performance polymeric films, new solvent‐soluble aromatic polyamides with a carbamoyl pendant group, namely poly(4,4′‐diamino‐3′‐carbamoylbenzanilide terephthalamide) (p‐PDCBTA) and poly(4,4′‐diamino‐3′‐carbamoylbenzanilide isophthalamide) (m‐PDCBTA), were synthesized. The polymers were cyclized at around 200 to 350 °C to form quinazolone and benzoxazinone units along the polymer backbone. The decomposition onset temperatures of the cyclized m‐ and p‐PDCBTAs were 457 and 524 °C, respectively, lower than that of poly(p‐phenylene terephthalamide) (566 °C). For the p‐PDCBTA film drawn by 40% and heat‐treated, the tensile strength and Young's modulus were 421 MPa and 16.4 GPa, respectively. The film cyclized at 350 °C showed a storage modulus (E′) of 1 × 10¹¹ dyne/cm² (10 GPa) over the temperature range of room temperature to 400 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 775–780, 2000     

New one step synthesis of 3,5‐disubstituted 1,2,4‐oxadiazoles

Disubstituted 1,2,4‐oxadiazoles have been synthesized in good yields and good purity in one pot procedure by reaction of aromatic nitriles, hydroxylamine hydrochloride and sodium carbonate in ethylene glycol under heating at 195°C. The structures of different 1,2,4‐oxadiazoles obtained were confirmed by ¹H, ¹³C NMR and mass spectroscopy.     

The reaction of (N‐isocyanimino) triphenylphosphorane with (E)‐3‐aryl‐2‐ propenoic acid derivatives: One‐pot synthesis of 2‐[(E)‐2‐aryl‐1‐ethenyl]‐1,3,4‐oxadiazoles via intramolecular aza‐Wittig reaction

The reaction of (E)‐3‐aryl‐2‐propenoic acid derivatives with (N‐isocyanimino) triphenylphosphorane proceeds smoothly at room temperature to afford the corresponding 2‐[(E)‐2‐aryl‐1‐ethenyl]‐1,3,4‐oxadiazole via an intramolecular aza‐Wittig reaction in good yields under neutral conditions. The structures of the products were deduced from their IR, ¹H NMR, and ¹³C NMR spectra and mass spectrometry. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:612–616, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20701