DBU-catalyzed expeditious and facile multicomponent synthesis of N-arylquinolines under microwave irradiation

Abstract  

N-Arylquinoline derivatives are obtained in excellent yields by a rapid, easy, and efficient one-pot multicomponent reaction of aromatic aldehydes, 3-arylamino-5,5-dimethylcyclohex-2-enone, and active methylene compounds utilizing 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst in ethanol under microwave irradiation.     

Microwave-assisted and scandium triflate catalyzed synthesis of tetrahydrobenzo[<Emphasis Type="Italic">a</Emphasis>]xanthen-11-ones

Abstract  

Synthesis of 12-aryl-8,9,10,12-tetrahydro-benzo[a]xanthen-11-ones was achieved by one-pot condensation of β-naphthol, substituted benzaldehydes, and 1,3-dicarbonyl compounds catalyzed by Sc(OTf)₃ under microwave irradiation in excellent isolated yields. The catalyst was recycled up to four cycles with no appreciable loss in catalytic activity. The compounds were evaluated for Src kinase activity and anticancer activity.     

Only acridine derivative from Hantzsch-type one-pot three-component reactions

Abstract  

A three-component Hantzsch-type condensation of different anilines with dimedone and benzaldehyde leads to the formation of a unique acridine derivative with an unusual breaking of a C–N bond. The reaction was also carried out employing rapid microwave or conventional heating and sonication as alternative energy sources, and only this 1,8-dioxodecahydroacridine was obtained.     

Different extraction methods of biologically active components from propolis: a preliminary study

Background  

Propolis is widely used in apitherapy, preparations, and food and beverage additives. Various extraction techniques were applied in the extraction of the biologically active constituents of poplar type propolis in order to compare their efficiency. The methods employed were: traditional maceration extraction, ultrasound extraction (UE), and microwave assisted extraction (MAE).     

Microwave-assisted rapid and efficient deprotection and direct esterification and silylation of MOM and EOM ethers catalyzed by [Hmim][HSO4] as a Br?nsted acidic ionic liquid

Abstract  

1-Methylimidazolium hydrogensulfate, [Hmim][HSO₄], a Br?nsted acidic room temperature ionic liquid, is used as a catalyst and reaction medium for facile and eco-friendly deprotection of methoxymethyl (MOM) and ethoxymethyl (EOM) ethers to their corresponding alcohols under thermal conditions (Δ) and microwave irradiation (MW). Furthermore, one-pot interconversion to the respective acetates and trimethylsilyl (TMS) ethers was also achieved.     

Microwave assisted solvent free synthesis of 1,3-diphenylpropenones

Background  

1,3-Diphenylpropenones (chalcones) are well known for their diverse array of bioactivities. Hydroxyl group substituted chalcones are the main precursor in the synthesis of flavonoids. Till date various methods have been developed for the synthesis of these very interesting molecules. Continuing our efforts for the development of simple, eco-friendly and cost-effective methodologies, we report here a solvent free condensation of aryl ketones and aldehydes using iodine impregnated alumina under microwave activation. This new protocol has been applied to a variety of substituted aryl carbonyls with excellent yield of substituted 1,3-diphenylpropenones.     

Intramolecular Diels–Alder cyclization of biodihydroxylated benzoic acid derivatives towards novel heterocyclic scaffolds

Abstract  

The potential of biodihydroxylated benzoic acid derivatives as versatile precursors for the construction of polycyclic scaffolds was investigated. Ralstonia eutropha B9 was used to biodihydroxylate sodium benzoate to sodium (1S,2R)-1,2-dihydroxycyclohexa-3,5-diene-1-carboxylate in high optical purity (>95% ee). The required cyclization precursors could be obtained in moderate to excellent yields after protection of the intermediate and subsequent functional group transformation. Intramolecular Diels–Alder cylizations were carried out under thermal or microwave conditions leading to enantiomerically pure products with five chiral centers.     

Green Synthesis of Some Calix[4]Resorcinarene Under Microwave Irradiation

A green synthetic procedure for the preparation of some calix[4]resorcinarenes using a household microwave oven has been carried out. This method represents a very rapid heating alternative to the conventional method that involves very long time of reactions (from 20-24 h in conventional heating to 5-8 min in microwave irradiation). C-4-hydroxy–3-methoxycalix[4]resorcinarene (CHMPCR), C-4-methoxyphenylcalix[4]resorcinarene (CMPCR) and C-2–phenylethenilcalix[4]resorcinarene (CPECR) was achieved by placed of resorcinol, an aldehyde, HCl and ethanol inside a household microwave oven. The product was recrystallized by methanol and analyzed by spectral analysis (FTIR, H-NMR and MS). Optimization of reaction was carried out in variation of microwave power, reaction times and reactant composition. The result shows that optimum condition of synthesis of C-4-hydroxy-3–methoxycalix[4]resorcinarene (CHMPCR) with microwave irradiation were at microwave power 332 W, reaction time 8 min and the mole ratio of resorcinol and 4-hydroxy-3-methoxyphenylbenzaldehyde 1:1. This parameter gave product in 97.8% (53.7% after recrystallization). The CPECR synthesis using resorcinol and cynnamaldehyde (1:1) at microwave power 332 W for 5 min afforded the product in 97.3% (44.5% after recrystallization). Whereas the reaction of resorcinol and 4-methoxyphenylbenzaldehyde (1:1.2) at microwave power 264 W for 5 min gave CMPCR in 99.5% (68.6% after recrystallization).     

Dissolution of sintered thorium dioxide in phosphoric acid using autoclave and microwave methods with detection by gamma spectrometry

A quantitative and fast method of dissolution of refractory thoria (ThO₂) was developed for the determination of thorium (Th) in a given sample. The dissolution of sintered ThO₂ powder, microspheres and pellets using 88% phosphoric acid was investigated. The conditions of quantitative dissolution of ThO₂ microspheres were optimized by conventional heating in autoclave and also by microwave heating. 100 mg of sintered ThO₂ microspheres were dissolved in 8 g of phosphoric acid in an autoclave, and heating at 170 °C for 3 h, in comparison to 5 g of phosphoric acid by microwave heating (375 W) at 220 °C for 1 h. Dissolution studies on the powder form of sintered ThO₂ were also performed. 1 g of sintered ThO₂ powder could be dissolved in 6.5 g of phosphoric acid in autoclave heating at 170 °C for 1 h. Strong complexing of (PO₄)³⁻ with Th⁴⁺ may be the influencing factor for quantitative dissolution of ThO₂.     

Microwave-enhanced cyanation of aryl halides with a dimeric <Emphasis Type="Italic">ortho</Emphasis>-palladated complex catalyst

Abstract  

A new dimeric ortho-palladated complex of 2-methoxyphenethylamine was synthesized and characterized and its application as a cyanation catalyst was investigated. The main advantages of this catalyst are its easy preparation, handling, stability, and moisture insensitivity. Thus, [Pd{C₆H₃(CH₂CH₂NH₂)-4-OMe-5-κ ²-C,N}(μ-Br)]₂ showed excellent catalytic activity for the cyanation of aryl iodides and bromides with K₄[Fe(CN)₆], in DMF in the presence of K₂CO₃ under microwave irradiation and conventional heating at 130 °C to give the desired cyanoarene products in good to high yields. The less reactive aryl chlorides also react with K₄[Fe(CN)₆] to give moderate yields of the aromatic nitriles. The effects of various parameters such as solvent, base, and amount of catalyst were studied. The reaction is suitable for a wide variety of substituted aryl halides with different electronic properties. Application of microwave irradiation improved the yields of the reactions and reduced the reaction times from hours to minutes.     

Synthesis and characterization of CaBi4Ti4O15 thin films annealed by microwave and conventional furnaces

CaBi₄Ti₄O₁₅ thin films were deposited by the polymeric precursor method and crystallized in a domestic microwave oven and conventional furnace. The films obtained for microwave energy are well-adhered, homogeneous and with good specularity when treated at 700 ^°C for 10 min. The microstructure and the structure of the films can be tuned by adjusting the crystallization conditions. When microwave oven is employed, the films presented bigger grains with mean grain size around 80 nm. For comparison, films were also prepared by the conventional furnace at 700 °C for 2 h.     

Electrochemical production of novel products from 2,3-dimethylhydroquinone in the presence of some β-diketones

Abstract  

Electrochemical oxidation of 2,3-dimethylhydroquinone has been studied in the presence of β-diketones as nucleophiles in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the derivatives of 2,3-dimethylhydroquinone participate in a Michael addition reaction to form the corresponding benzofuran derivatives. The electrochemical synthesis has been successfully performed at pH 7.0 and E = 0.1 V versus an Ag|AgCl|KCl (3 M) in an undivided cell in good yield and purity.     

Application of chloroaluminate ionic liquid as catalyst and medium for the dealkylation of esters

Abstract  

Dealkylation of esters to carboxylic acids was performed using chloroaluminate ionic liquids (PyHBr/AlCl₃, PyHCl/AlCl₃, Me₃NHCl/AlCl₃, Et₃NHCl/AlCl₃) as catalyst and medium. The catalytic activity of PyHBr/AlCl₃ (X(AlCl₃) = 0.67) proved to be superior to the other three ionic liquids for the dealkylation of methyl benzoate with a conversion of 97% after 3 h at 140 °C. After easy separation from the products the ionic liquid PyHBr/AlCl₃ could be reused six times without loss of its activity.     

Direct synthesis of nitriles from aldehydes using tetrabutylammonium tribromide in aqueous ammonia

Abstract  

A convenient method for direct conversion of aldehydes into nitriles has been developed by using tetrabutylammonium tribromide in aqueous ammonia.     

Synthesis and microwave dielectric properties of Ca<Subscript>0.6</Subscript>La<Subscript>0.267</Subscript>TiO<Subscript>3</Subscript> nanocrystalline powders by sol–gel method

Ca_0.6La_0.267TiO₃ nanocrystalline powders were successfully synthesized by the sol–gel method using PEG1000 as a dispersant in this study. The sinterability of the powders and the microwave dielectric properties of the ceramics were also investigated. The XRD diffraction result showed that pure Ca_0.6La_0.267TiO₃ powder with orthorhombic perovskite structure could be synthesized at 600 °C for 2 h without any detectable intermediate phase. The average grain size of the as-synthesized powder was as low as 35 nm. Compared with Ca_0.6La_0.267TiO₃ ceramics fabricated by conventional solid-state process, the bulk materials prepared by sintering as-prepared nanopowders performed better in densification and microwave dielectric properties. The ceramics sintered at 1,300 °C exhibited a higher relative density of 98.3% combined with a dielectric constant (ε _r ) of 120.3, a quality factor (Q × f) of 23,550 GHz and a temperature coefficient of resonant frequency (τ _f ) of +220.7 ppm/°C, respectively.     

Palladium tetrazole–supported complex as an efficient catalyst for the Heck reaction

Abstract  

A tetrazole-supported polymeric ligand has been synthesized. The palladium complex derived from the polymeric material has been evaluated as a catalyst for the Heck reaction of aryl iodides and bromides with styrene to provide the corresponding products in high yields. The reaction proceeded smoothly in the presence of 1 mol% with respect to Pd of catalyst in DMF at 125 or 140 °C within 1–3 h. Recycling studies showed that the catalyst can be readily recovered and reused for several times without significant loss of catalytic activity.     

Enantioselective synthesis of 1-arylethanediols by rhodium-catalyzed transfer hydrogenation of α-tosyloxyarylketones

Abstract  

Catalytic transfer hydrogenation of α-tosyloxyarylketones mediated by a chiral rhodium complex using an azeotropic mixture of formic acid/triethylamine afforded the corresponding 1-arylethanediol monotosylates in excellent yield with high enantioselectivity.     

Enhanced rate of intramolecular nitrile oxide cycloaddition and rapid synthesis of isoxazoles and isoxazolines

Abstract  

An enhanced rate of intramolecular nitrile oxide cycloaddition and hence a rapid synthesis of isoxazoles and isoxazolines is described. Formation of nitrile oxides from oximes using only 1 or 2 Eq (equivalents) of aqueous sodium hypochlorite solution is also described.     

An efficient synthesis of β-aminoketone compounds through three-component Mannich reaction catalyzed by calcium chloride

Abstract  

Various β-aminoketones were synthesized in a three-component reaction of ketones, aldehydes, and amines in the presence of calcium chloride as catalyst in ethanol in high yields as compared to other synthetic methods. The advantages of this new method are a short reaction time (2 h), high yields, easy workup, convenience, low cost, and eco-friendly protocol.     

Effect of ZnO on sintering and microwave dielectric properties of 0.5CaTiO3-0.5 (Li0.5La0.5) TiO3 ceramics

The novel calcium titanate-lithium lanthanum titanate doped with zinc oxide (0.10, 0.30, and 0.50 mol. %) ceramic samples were prepared by solid-state reaction route. The phase formation, microstructure, densification, and microwave dielectric properties were investigated. It was found that the doping with zinc oxide led to a decrease in sintering temperature by 25 ^oC as compared with pure calcium titanate lithium lanthanum titanate due to the liquid phase effect. Also, the calcium titanate lithium lanthanum titanate (10ZCTLLT&30ZCTLLT)) doped with lower zinc oxide (0.10 and 0.30 mol. %) led to higher densification parameter. This was followed by increasing the zinc oxide doping up to (0.50 mol. %) which resulted in a decrease in densification and microwave dielectric properties which may be attributed to increase in porosity and grain growth upon the evaporation of zinc and oxygen vacancy. This led to the increase in dielectric loss (≈10 × 10^?4) value with 50ZCTLLT. Hence, the best result of microwave dielectric characteristics was obtained for 0.5CaTiO₃–0.5(Li_0.5La_0.5)TiO₃ with (0.10 and 0.30 mol. % ZnO) 10ZCTLLT and 30ZCTLLT ceramic samples sintered at 1175 ^oC/2h, with low dielectric constant (ε_r) = 4.4–10.5, very low dielectric loss = 1.07-2.23 × 10^?4 and high quality factor (Q x ?) ≈59-55 × 10⁴ at 8 GHz. Consequently, they can be used not only in wireless satellite communications technology but also can be used in the fifth-generation telecommunication 5G technology construction.