Sodium halides as the source of electrophilic halogens in green synthesis of 3-halo- and 3,n-dihalobenzo[b]thiophenes

A convenient methodology for the synthesis of mono- and di-halogenated benzo[b]thiophenes is described herein, which utilizes copper(II) sulfate pentahydrate and various sodium halides in the presence of substituted 2-alkynylthioanisoles. The proposed method is facile, uses ethanol as a green solvent, and results in uniquely substituted benzo[b]thiophene structures with isolated yields up to 96%. The most useful component of this methodology is the selective introduction of bromine atoms at every available position (2–7) around the benzo[b]thiophene ring, while keeping position 3 occupied by a specific halogen atom such as Cl, Br or I. Aromatic halogens are useful reactive handles; therefore, the selective introduction of halogens at specific positions would be valuable in the targeted synthesis of bioactive molecules and complex organic materials via metal-catalyzed cross coupling reactions. This work is a novel approach towards the synthesis of dihalo substituted benzo[b]thiophene core structures, which provides a superior alternative to the current methods discussed herein.     

Synthesis and characterization of dimeric μ-oxidovanadium complexes as the functional model of vanadium bromoperoxidase

Two vanadium (IV) complexes [V^IVO(Haeae-sal)(MeOH)]⁺ ( 1 ) and [V^IVO(Haeae-hyap)(MeOH)]⁺ ( 2 ) were prepared by reacting [VO(acac)₂] with ligands [H₂aeae-sal] ( I ) and [H₂aeae-hyap] ( II ) respectively. Condensation of 2-(2-aminoethylamino)ethanol with salicylaldehyde and 2-hydroxyacetophenone produces the ligands ( I ) and ( II ) respectively. Both vanadium complexes 1 and 2 are sensitive towards aerial oxygen in solution and rapidly convert into vanadium(V) dioxido species. Vanadium(V) dioxido species crystalizes as the dimeric form in the solid-state. Single-crystal XRD analysis suggests octahedral geometry around each vanadium center in the solid-state. To access the benefits of heterogeneous catalysis, vanadium(V) dioxido complexes were anchored into the polymeric chain of chloromethylated polystyrene. All the synthesized neat and supported vanadium complexes have been studied by a number of techniques to confirm their structural and functional properties. Bromoperoxidase activity of the synthesized vanadium(V) dioxido complexes 3 and 4 was examined by carrying out oxidative bromination of salicylaldehyde and oxidation of thioanisole. In the presence of hydrogen peroxide, 3 shows 94.4% conversion ( TOF value of 2.739 × 10² h⁻¹) and 4 exhibits 79.0% conversion (TOF value of 2.403 × 10² h⁻¹) for the oxidative bromination of salicylaldehyde where 5-bromosalicylaldehyde appears as the major product. Catalysts 3 and 4 also efficiently catalyze the oxidation of thioanisole in the presence of hydrogen peroxide where sulfoxide is observed as the major product. Covalent attachment of neat catalysts 3 and 4 into the polymer chain enhances substrate conversion (%) and their catalytic efficiency increases many folds, both in the oxidative bromination and oxidation of thioether. Polymer supported catalysts 5 displayed 98.8% conversion with a TOF value of 1.127 × 10⁴ h⁻¹ whereas catalyst 6 showed 95.7% conversion with a TOF value of 4.675 × 10³ h⁻¹ for the oxidative bromination of salicylaldehyde. These TOF values are the highest among the supported vanadium catalysts available in the literature for the oxidative bromination of salicylaldehyde.     

Receptor design and extraction of inorganic fluoride ion from aqueous medium

A receptor with acidic methylene hydrogens is found to act as an efficient binding mode for F(-). This reagent could as well be used for selective and quantitative extraction of F(-) from the aqueous solution of NaF and sea water.     

Bis coumarinyl bis triazolothiadiazinyl ethane derivatives: Synthesis,antiviral activity evaluation,and molecular docking studies

A series of novel 3,3′-(3,3′-(dihydroxy/hydroxyethane-1,2-diyl)bis(7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine-6,3-diyl))bis(2H-chromen-2-ones) were prepared by the condensation of thiocarbohydrazide with tartaric acid or malic acid followed by various 3-(2-bromoacetyl)-2H-chromen-2-ones in two steps with good yields. All the synthesized compounds were characterized by analytical and spectral (IR, ¹H NMR, ¹³C NMR, and mass) data. These synthesized bis(triazolothiadiazinyl coumarin) compounds were evaluated for broad spectrum of antiviral activity. Among all the tested compounds, compound 5f exhibited antiviral activity against H1N1 virus. The molecular docking studies of these compounds against H1N1 neuraminidase enzyme were performed. The binding affinity and binding values were compared with standard drugs.     

Synthesis of 3,4-disubstituted 2H-benzopyrans through C-C bond formation via electrophilic cyclization

The electrophilic cyclization of substituted propargylic aryl ethers by I2, ICl, and PhSeBr produces 3,4-disubstituted 2H-benzopyrans in excellent yields. This methodology results in vinylic halides or selenides under mild reaction conditions and tolerates a variety of functional groups, including methoxy, alcohol, aldehyde, and nitro groups.     

Anion recognition through hydrogen bonding by adamantane-dipyrromethane receptors

Adamantane-dipyrromethane (AdD) receptors [di(pyrrole-2-yl)methyladamantane (1), 2,2-di(pyrrole-2-yl)adamantane (2), 1,3-bis[di(pyrrole-2-yl)methyl]adamantane (3), 2,2,6,6-tetra(pyrrole-2-yl)adamantane (4)] form complexes with F⁻, Cl⁻, Br⁻, AcO⁻, NO₃⁻, HSO₄⁻, and H₂PO₄⁻. The association constants of the complexes were determined by ¹H NMR titrations, whereas the geometries of complexes 1·F⁻ (2:1), 2·F⁻ (2:1), 2·Cl⁻ (2:1), 2·AcO⁻ (2:1), and 4·F⁻ (1:1) were determined by X-ray structural analysis. The most stable complexes are of 2:1 stoichiometry with F⁻ and AcO⁻. The stability constants are in accordance with the anion basicity and the ability of AdD receptors to place the hydrogen bonding donor groups in a tetrahedral fashion around anions. The binding energies of the complexes between receptors 1-4 and F⁻ anion are calculated using quantum chemical methods. The calculated results show that the solvent polarity is important for the complexation of fluoride ion with AdD receptors 1-4.     

Benzylic C-H activation and C-O bond formation via aryl to benzylic 1,4-palladium migrations

A procedure for benzylic C-H activation has been developed using a palladium 1,4-aryl to benzylic migration as a key step. Carboxylates and phenoxides readily trap the resulting benzylic palladium intermediates obtained from palladium ‘through space’ migration. Aryl bromides and iodides have been successfully employed in this reaction, furnishing moderate to good yields. The mechanism of this reaction has been studied by deuterium-labeling experiments, which suggest that the migration of palladium from an aryl to a benzylic position occurs reversibly. The reaction conditions developed for the migration process also oxidize the neighboring benzylic alcohols to the corresponding aldehydes and ketones.     

Probing the structural and electronic effects to stabilize nonplanar forms of thioamide derivatives: A computational study

Density functional calculations have been performed to examine the stability of nonplanar conformations of thioamide derivatives. Electrostatic, orbital, and ring strain effects were invoked to stabilize the nonplanar conformations of thioamide systems 2 – 7 . Electrostatic interactions helped to achieve the twisted forms of thioamide derivatives; however, pyramidal forms predicted to be the global minimum. Negative hyperconjugative type interactions enhanced the stability of the twisted form 4b when compared with the planar form 4a . The influence of ring strain effect to achieve the twisted form of thioamide was observed with azirine ring. The predictions made with B3LYP/cc‐pVDZ+ level of theory was found to be in good agreement with more accurate CBS‐QB3 method. The solvent calculations performed with polarized continuum solvation model suggest that the relative stabilities of the nonplanar forms of thioamide derivatives are in general similar to the gas phase results. The importance of hydrogen bonding interactions between the solvent molecules and thioamide derivatives was observed toward the enhanced stability of twisted forms using a combination of explicit solvent molecules and continuum model. The natural bond orbital analysis confirmed the participation of n_N → π*_C?S delocalizations in the planar forms and corroborated the earlier reports on larger delocalizations in thioamide systems. Furthermore, the influence of electrostatic and ring strain effects on the amide, natural amides, and selenoamide has also been studied. © 2011 Wiley Periodicals, Inc. J Comput Chem 2011     

Study of ion transport and materials properties of K+-ion conducting solid polymer electrolyte (SPE): [(1-x) PEO: xCH3COOK]

Study of ion transport behavior in K⁺-ion conducting solid polymer electrolyte (SPE) films: [(1-x) PEO: xCH₃COOK] has been reported. Poly (ethylene oxide) PEO has been used as polymeric host and potassium acetate: CH₃COOK as complexing salt. SPE films in varying salt concentrations have been prepared by hot-press cast method. SPE film: [95PEO: 5CH₃COOK] has been identified as Optimum Conducting Composition (OCC) with room temperature conductivity (σ _rt) ~ 2.74 × 10⁻⁷ S/cm. As a consequence of salt complexation in polymeric host, σ _rt-enhancement of approximately two orders of magnitude was achieved in SPE OCC film. Ion transport property has been characterized in terms of ionic conductivity (σ), total ionic (t _ion)/cation (t ₊) transference numbers using different ac/dc techniques. Temperature-dependent conductivity measurement was done to explain mechanism of ion transport and to evaluate activation energy (E _a). XRD, FTIR, and DSC techniques were used to study materials property in SPE OCC film which also confirmed the complexation of salt in the polymeric host as well as increase in degree of amorphousity.