H5BW12O40 as a green and efficient homogeneous but recyclable catalyst in the synthesis of 4H‐Pyrans via multicomponent reaction

Keggin‐type heteropolyacid, H₅BW₁₂O₄₀ (BWA) with a higher negative charge and stronger Brønsted acidity comparing to Si and P derivatives was used as an efficient, green, and reusable catalyst in a three‐component reaction involving the cyclocondensation of various β‐dicarbonyl compounds, differently substituted aromatic aldehydes and malononitrile in EtOH/H₂O for the facile, clean, and high yielding synthesis of 4H‐pyrans. All reactions were completed in short times and the products were obtained in good to excellent yields. The reaction medium could be recycled and reused several times without any loss of efficiency.     

Efficient synthesis of novel functionalized pyrazolo-pyranoquinoline and tetrahydrodibenzo-[1,8]naphthyridinone derivatives

The facile and efficient synthesis of 1,4-dihydropyrazolo-pyrano-[2,3-b]quinoline derivatives from the reaction of 2-chloroquinoline-3-carbaldehydes and pyrazolones is described. Moreover, a one-pot method for the development of functionalized tetrahydrodibenzo[b,g][1,8]naphthyridinone derivatives is reported by using a three-component reaction of 2-chloroquinoline 3-carbaldehydes, pyrazolone, and enaminones catalyzed by l-proline in EtOH.     

Strong Microheterogeneity in Novel Deep Eutectic Solvents

With the increasing application of template assisted syntheses in deep eutectic solvents and successful application of hydrophobic deep eutectic solvents in extraction processes, where microheterogeneity plays a major role, suggestions for novel deep eutectic solvents which exhibit strong microheterogeneity are desirable. Therefore, classical molecular dynamics simulations were carried out on deep eutectic solvent systems constructed of choline chloride and some of its derivatives mixed with ethylene glycol in a molar composition of 1 : 2 since this is the optimal parent composition. The derivatives consisted of a series of elongated alkyl side chains and elongated alcohol side chains. Of these series only choline chloride ethylene glycol has been investigated experimentally, the other systems are suggested and theoretically investigated as possible target for synthesis. Our domain analysis supported by the clear distinction of polar and nonpolar parts from the electrostatic potentials reveals that strong microheterogeneity within these novel hypothetical deep eutectic solvents exists. Rather stretched than crumbled side chains maximize possible interaction sites for both polar and nonpolar parts which make the suggested compounds valuable objectives for experiments in order to exploit the microheterogeneity in deep eutectic solvents.     

Characterization of intermolecular interactions in crystalline aspirin: A computational NQR study

A computational study at the level of density functional theory was carried out to characterize the ¹⁷O and ²H nuclear quadrupole resonance (NQR) spectroscopy parameters in crystalline aspirin. To include O? H···O and C? H···O hydrogen bonding effects in the calculations, the most probable interacting molecules with the target molecule in the crystalline phase were considered through a pentamer cluster. The NQR calculations were performed with BLYP, B3LYP, and M06 functionals employing 6‐311++G** and Jensen's polarization‐consistent pcJ‐1 basis sets. Linear correlations are observed between the calculated ¹⁷O and ²H NQR parameters and the hydrogen bond strengths, suggesting the possibility of estimating hydrogen bonding information from calculated NQR data. Different contributions of various nuclei to hydrogen bonding interactions and observed trends of calculated NQR parameters are well justified by atoms in molecules analyses at the BCPs of these interactions. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Oxidation state and symmetry of magnesia-supported Pd13O(x) nanocatalysts influence activation barriers of CO oxidation

Combining temperature-programmed reaction measurements, isotopic labeling experiments, and first-principles spin density functional theory, the dependence of the reaction temperature of catalyzed carbon monoxide oxidation on the oxidation state of Pd(13) clusters deposited on MgO surfaces grown on Mo(100) is explored. It is shown that molecular oxygen dissociates easily on the supported Pd(13) cluster, leading to facile partial oxidation to form Pd(13)O(4) clusters with C(4v) symmetry. Increasing the oxidation temperature to 370 K results in nonsymmetric Pd(13)O(6) clusters. The higher symmetry, partially oxidized cluster is characterized by a relatively high activation energy for catalyzed combustion of the first CO molecule via a reaction of an adsorbed CO molecule with one of the oxygen atoms of the Pd(13)O(4) cluster. Subsequent reactions on the resulting lower-symmetry Pd(13)O(x) (x < 4) clusters entail lower activation energies. The nonsymmetric Pd(13)O(6) clusters show lower temperature-catalyzed CO combustion, already starting at cryogenic temperature.     

A Sharp Jump in Photocatalytic Activity of Elemental Sulfur for Dye Degradation in Alkaline Solution

Elemental sulfur is a low-cost and abundant substance as one of the largest by-products of the oil industry which was widely used in many industrial activities. Cyclo-octasulfur (S₈) is one of the sulfur allotropes that is a very stable substance in standard conditions. In this study, we report a low-cost and fast method for the degradation of methyl violet in water under visible light and also sunlight by using elemental sulfur (S₈). The results show that sulfur is a good photocatalyst which operates under visible light and can be utilized for degradation of methyl violet. The photocatalytic degradation of methyl violet in acidic, neutral, and alkaline media was investigated, and it was found that the photocatalytic efficiency increases dramatically in alkaline solution. The effects of the initial concentration of the dye, photocatalyst dosage, solution pH, and photocatalyst reusability were investigated. The kinetics of the reaction were studied in detail, and the photocatalytic rate equation was presented.     

Current applications of organocatalysts in asymmetric aldol reactions: An update

The aldol reaction is one of the most important carbon–carbon bond formations in synthetic organic chemistry. An enantioselective aldol reaction should provide an enantioenriched product. The organocatalytic asymmetric aldol reaction via an in situ generated enamine intermediate is one of the most powerful synthetic tools to achieve enantiomerically pure products. This approach is often used to obtain chiral β-hydroxycarbonyl compounds with excellent enantioselectivity. In this report, we update our previous review regarding the applications of organocatalysts in asymmetric aldol reactions leading to chiral β-hydroxycarbonyl compounds as versatile synthetic motifs frequently found in pharmaceutically desired intermediates and biologically active naturally occurring compounds.     

Variation in essential oil composition of Teucrium hircanicum L. from Iran-A rich source of (E)-α-bergamotene

In present work, the chemical composition of the essential oils obtained from dried flowering aerial parts of Teucrium hircanicum L. (Labiatae) originated from ten wild populations in Iran was analyzed by a GC-FID and GC/MS system. The oil yields varied from 0.04% to 0.1%. A total of thirty-two compounds representing 67.6–97.7% of the oil were identified. The essential oil was found to be rich in sesquiterpene hydrocarpons (E)-α-bergamotene (17.5–86.9%) and (E)-β-farnesene (0.5–21.4%). Of the total identified compounds, sesquiterpene hydrocarpons (36.1–89.7%) were included the greatest essential oil fraction in all the populations, followed by oxygenated monoterpenes (2.2–21.6%), oxygenated sesquiterpenes (0.0–14.4%) and monoterepene hydrocarbons (0.0–9.5%). Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) were used to distinguish any geographical variations, indicating that the clustering of populations is related to their geographic origin. According to the GC/MS analysis, two chemotypes consisting of (E)-α-bergamotene and (E)-α-bergamotene-(E)-β-farnesene were identified in the populations.     

Organocatalyzed Asymmetric Friedel‐Crafts Reactions: An Update

The Friedel‐Crafts alkylation (F‐CA) reaction is a special kind of carbon?carbon bond formations, which is frequently being used for the formation of such bond in some aromatic rings in organic synthesis. Its asymmetric variant gives enantiorich products. Commonly, an in situ organocatalyzed asymmetric Friedel‐Crafts alkylation (AF‐CA) proceeds via generation of an enamine as an intermediate. The organocatalyzed‐AF‐CA was discovered and established in the mid‐1980s and reviewed comprehensively in 2010. In this report, we are trying to update the applications of novel organocatalysts in the AF‐CA as a versatile synthetic strategy, which is frequently used in the effective asymmetric synthesis of complex molecules, pharmaceutically important compounds and most importantly in the total synthesis of biologically active natural products.