Au(I)/Ag(I)-catalyzed annulation of sugar aldehyde tethered with 3-phenylprop-2-yn-1-yl ether with aryl amines for the pyrano[4,3-b]quinoline derivatives

Aryl amines undergo smooth annulation with O-phenylpropynyl sugar aldehyde in the presence of the Ph₃PAuCl (10 mol %)/AgSbF₆ (10 mol %) catalytic system to afford the corresponding tetrahydro-3aH-spiro[[1,3]dioxolo[4″,5″:4′,5′]furo[3′,2′:5,6]pyrano[4,3-b]quinoline-2,1′-cyclohexane] derivatives in good yields and selectivity.     

Gold-catalyzed cyclization of enyne-1,6-diols to substituted furans

Treatment of enyne-1,6-diols with 5 mol % Ph₃PAuCl in the presence of 5 mol % AgOTf as a cocatalyst selectively produced trisubstituted furans in good to excellent yields in dichloromethane at room temperature for 5-10 min through cyclization followed by isomerization.     

Gold-catalyzed consecutive [1,2] alkyl migration-oxygen transfer reaction of 2-alkynyl-1-tetralones

Gold-catalyzed isomerization of 2-alkynyl-1-tetralones afforded the corresponding 2-naphthylmethyl ketones in good to high yields. For example, the reaction of 2-{4-(methoxyphenyl)methyl}-2-(phenylethynyl)-3,4-dihydronaphthalen-1(2H)-one and 2-benzyl-2-(phenylethynyl)-3,4-dihydronaphthalen-1(2H)-one in the presence of 5 mol % of (Ph₃P)AuCl and 5 mol % of AgOTf in THF at 50 °C gave 2-{1-(4-methoxyphenylmethyl)naphthalen-2-yl}-1-(4-methoxyphenyl)ethanone and 2-(1-benzylnaphthalen-2-yl)-1-phenylethanone in 85% and 96% yields, respectively. The present reaction proceeds through [1,2] alkyl migration followed by oxygen transfer.     

Chemo- and diastereoselective Bi(OTf)3-catalyzed benzylation of silyl nucleophiles

The direct alkylation of silyl enol ethers with para-methoxybenzylic alcohols or their corresponding acetates was efficiently catalyzed by Bi(OTf)₃ in CH₃NO₂ as the solvent. The reaction provided the α-benzylated carbonyl compounds in high yields after short reaction times using 1-2.5 mol % of the catalyst. Benzylic acetates other than para-methoxybenzylic acetates also underwent the reaction. High facial diastereoselectivities were observed with acetates derived from chiral α-branched para-methoxybenzylic alcohols. In addition, a catalytic reduction with Et₃SiH as the reducing agent is reported.     

Cross coupling of 3-bromopyridine and sulfonamides (RNHSO2R·R = H, Me, alkyl; R = alkyl and aryl) catalyzed by CuI/1,3-di(pyridin-2-yl)propane-1,3-dione

N-(3-Pyridinyl)-substituted secondary and tertiary sulfonamides have been synthesized in good to excellent yields by the reaction of 3-bromopyridine with primary and secondary alkyl and aryl sulfonamides (MeSO₂NH₂, MeSO₂NHMe, TolSO₂NH₂, TolSO₂NHMe, 1,3-propanesultam, and 1,4-butanesultam), catalyzed by CuI (20 mol %) and 1,3-di(pyridin-2-yl)propane-1,3-dione (20 mol %) with K₂CO₃ (200 mol %) in DMF (0.17 M for ArBr) at 110-120 °C over 36-40 h. 2-Bromopyridine, 4-bromopyridine, and a wide variety of substituted phenyl bromides can also be successfully coupled with sulfonamides under these reaction conditions.     

Ru3(CO)12-catalyzed intramolecular allylic transfer reaction of tethered carbonyl group and allylic acetate moiety

A ruthenium catalyzed intramolecular allylic transfer reaction of allylic acetates containing aldehydes or ketones to form cis-homoallylic cyclopentanols and cyclohexanols as a major component is described. The use of Ru₃(CO)₁₂ (1 mol %) to promote reaction results in a convenient procedure for intramolecular allylation of carbonyl functionalities.     

Synthesis of new trifluoromethyl peptidomimetics with a triazole moiety

gem-Chloroamine CF₃CH(Cl)NHAc 1 reacts in a one-pot sequence with NaN₃ to afford trifluoromethyl azido compound 2 and further undergoes a Huisgen 1,3-dipolar cycloaddition with alkynes to yield 1,4-disubstitued 1,2,3-triazoles. The reaction is catalyzed by Cu(II) species (Cu(OAc)₂, 10 mol %) without any reducing agent, and the corresponding products are afforded in high yields (74-87%). This process offers thus an entry to new trifluoromethyl pseudopeptides.     

Aqueous media carboxylative cyclization of propargylic amines with CO2 catalyzed by amphiphilic dendritic N-heterocyclic carbene–gold(I) complexes

We prepared amphiphilic dendritic N-heterocyclic carbene (NHC)–gold(I) complexes having poly(ethylene glycol) units at the peripheral layer. By employing 1 mol % of the dendritic NHC–gold(I) catalyst, the aqueous media carboxylative cyclization of propargylic amines proceeded smoothly to provide the corresponding 2-oxazolidinone under atmospheric pressure of CO₂ at room temperature.     

Achiral β-amino alcohols as efficient ligands for the ruthenium-catalysed asymmetric transfer hydrogenation of sulfinylimines

Some achiral β-amino alcohols have been shown as efficient ligands for the ruthenium-catalysed asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)imines in isopropanol. The ruthenium complex prepared from [RuCl₂(p-cymene)]₂ (2.5 mol %) and 2-amino-2-methyl-1-propanol (5 mol %) leads to α-branched chiral primary amines with very high optical purities (up to 98% ee) by the diastereoselective reduction of the imines followed by removal of the sulfinyl group under mild acidic conditions. Short reaction times (2-3 h) were needed to complete the reduction reactions when they were performed at 50 °C.     

Sorption characteristics and chromatographic separation of gold (I and III) from silver and base metal ions using polyurethane foams

The influence of different parameters on the sorption profiles of trace and ultra traces of gold (I) species from the aqueous cyanide media onto the solid sorbents ion exchange polyurethane foams (IEPUFs) and commercial unloaded polyurethane foams (PUFs) based polyether type has been investigated. The retention of gold (I) species onto the investigated solid sorbents followed a first-order rate equation with an overall rate constant k in the range 2.2-2.8 ± 0.2 s⁻¹. The sorption data of gold (I) followed Freundlich and Langmuir isotherm models. Thus, the a dual-mode of sorption mechanism involving absorption related to “weak base anion exchanger” and an added component for “surface adsorption” seems the most likely proposed dual mechanism for retention profile of gold (I) by the IEPUFs and PUFs solid sorbents. The capacity of the IEPUFs and PUFs towards gold (I) sorption calculated from the sorption isotherms was found to be 11.21 ± 1.8 and 5.29 ± 0.9 mg g⁻¹, respectively. The chromatographic separation of the spiked inorganic gold (I) from de ionized water at concentrations 5-15 μg mL⁻¹ onto the developed IEPUFs and PUFs packed columns at 10 mL min⁻¹ flow rate was successfully achieved. The retained gold (I) species were then recovered quantitatively from the IEPUFs (98.4 ± 2.4%, n = 5) and PUFs (95.4 ± 3.4%, n = 5) packed columns using perchloric acid (60 mL, 1.0 mol L⁻¹) as a proper eluating agent. Thiourea (1.0 mol L⁻¹)-H₂SO₄ (0.1 mol L⁻¹) system was also used as eluating agent for the recovery of gold (I) from IEPUFS (95.4 ± 5.4%, n = 3) and also PUFs (93.4 ± 4.4%, n = 3) packed columns. The performance of the IEPUFs and PUFs packed columns in terms of the height equivalent to the theoretical plates (HETP), number of plates (N), and critical and breakthrough capacities towards gold (I) species were evaluated. The developed IEPUFs packed column was applied successfully for complete retention and recovery (98.5 ± 2.7) of gold (III) species spiked onto tap- and industrial wastewater samples at <10 μg Au mL⁻¹ after reduction to gold (I). The IEPUFs packed column was applied satisfactorily for complete retention and recovery (98.5 ± 2.7) of total inorganic gold (I) and/or gold (III) species spiked to tap- and industrial wastewater samples at <10 μg mL⁻¹ gold. Chromatographic separation of gold (I) from silver (I) and base metal ions (Fe, Ni, Cu and Zn) using IEPUFS packed columns was satisfactorily achieved. The proposed method was applied successfully for the pre-concentration and separation from anodic slime and subsequent FAAS determination of analyte with satisfactory results (recoveries >95%, relative standard deviations <4.0%).     

Ammonium salt catalyzed oxidation of organosulfides to organosulfoxydes

The selective oxidation of aromatic and aliphatic organosulfides with H₂O₂/H₂O catalyzed by metal free ammonium salts has been explored. Reactions were performed using 2.5–5 mol % of catalyst loadings, isolating the corresponding sulfoxides in good to excellent yields (75–93%) and high selectivity.     

Copper mediated atom transfer radical cyclisations with AIBN

We have shown that it is possible to mediate a range of 5-exo trig and 5-exo dig atom transfer radical cyclisations of bromoacetamides using 0.1-1 mol % CuBr or CuBr₂ in conjunction with 0.1-1 mol % tri(pyridin-2-ylmethyl)amine and 10 mol % AIBN. This equates to a 30-300-fold reduction in the amount of catalyst previously reported for these reactions and allows cyclisation to be carried out with the more oxidatively stable CuBr₂ without the requirement of an inert atmosphere.     

Gamma radiation induced synthesis of gold nanoparticles in aqueous polyvinyl pyrrolidone solution and its application for hydrogen peroxide estimation

Gold nanoparticles (Au nps) have been synthesized in aqueous solution of polyvinyl pyrrolidone (PVP) by gamma radiolysis from HAuCl₄·3H₂O precursor and in presence of small concentrations of Ag⁺, 2-propanol and acetone. The effect of different experimental parameters, such as concentration of reactant, molecular weight of PVP on nanoparticle formation was studied. TEM image confirmed that spherical Au nps were formed when PVP of molecular weight 360,000 Da was used as capping agent. H₂O₂ is a reactant in the enzyme catalyzed reaction of o-phenylene diamine (o-PDA). The reaction product has a weak absorption in the yellow region of the spectrum. When this product interacts with Au nps, it leads to enhancement of the absorption peak. The nanoparticles synthesized by radiation method were used for estimation of H₂O₂. The absorbance value of this peak at λ_max was observed to change with H₂O₂ concentration, which was monitored for estimation of H₂O₂. The response is linear in the range of 2.5×10⁻⁶ mol dm⁻³ to 2×10⁻⁴ mol dm⁻³ and 1×10⁻⁷ mol dm⁻³ to 3×10⁻⁶ mol dm⁻³ H₂O₂ in two separate sets of experimental parameters with detection limit 1×10⁻⁷ mol dm⁻³.     

Determination of benorilate in pharmaceutical formulations and its metabolite in urine at carbon paste electrode modified by silver nanoparticles

Benorilate was determined by the differential pulse voltammetry (DPV) using a carbon paste electrode modified by silver nanoparticles in 1.25 × 10⁻³ mol l⁻¹ KH₂PO₄ and Na₂HPO₄ buffer solution (pH = 6.88, 25 °C) .The anodic peak potential was +0.970 V (versus SCE). A good linear relationship was realized between the anodic peak currents and benorilate concentrations in the range of 1.0 × 10⁻⁷ to 2.5 × 10⁻⁴ mol l⁻¹ with the detection limit of 1.0 × 10⁻⁸ mol l⁻¹. The recovery was 95.2-103.6% with the relative standard deviation of 3.6% (n = 9). The pharmaceutical preparations, benorilate tablets samples and its metabolite (salicylic acid) in urine were determined with the desirable results.     

Rhodium-catalyzed alkylthio exchange reaction of thioester and disulfide

The Wilkinson complex RhCl(PPh₃)₃ catalyzes equilibrating alkylthio exchange reaction of thioesters with disulfides. The treatment of a thioester and a dialkyl disulfide in refluxing diethyl ketone in the presence of RhCl(PPh₃)₃ (2.5 mol %) for 1.5 h gave an alkylthio exchanged thioester. The reaction of S-methyl ester was conducted shifting the equilibrium by removing volatile dimethyl disulfide.     

Improvement of microwave-assisted digestion of milk powder with diluted nitric acid using oxygen as auxiliary reagent

The feasibility of using diluted HNO₃ solutions under oxygen pressure for decomposition of whole and non-fat milk powders and whey powder samples has been evaluated. Digestion efficiency was evaluated by determining the carbon content in solution (digests) and the determination of Ca, Cd, Cu, Fe, K, Mg, Mn, Mo, Na, Pb and Zn was performed by inductively coupled plasma optical emission spectrometry and Hg by chemical vapor generation coupled to inductively coupled plasma mass spectrometry. Samples (up to 500 mg) were digested using HNO₃ solutions (1 to 14 mol L^− 1) and the effect of oxygen pressure was evaluated between 2.5 and 20 bar. It was possible to perform the digestion of 500 mg of milk powder using 2 mol L^− 1 HNO₃ with oxygen pressure ranging from 7.5 to 20 bar with resultant carbon content in digests lower than 1700 mg L^− 1. Using optimized conditions, less than 0.86 mL of concentrated nitric acid (14 mol L^− 1) was enough to digest 500 mg of sample. The accuracy was evaluated by determination of metal concentrations in certified reference materials, which presented an agreement better than 95% (Student's t test, P < 0.05) for all the analytes.     

2,2′-Dilithiobiphenyl by direct lithiation of biphenylene

The reaction of biphenylene (1) with an excess of lithium powder (1:14 molar ratio) and a catalytic amount of DTBB (10 mol %) in THF at room temperature leads to the formation of the dilithiated species I by reductive opening of the four-membered ring. Further reaction of this intermediate with different electrophiles [Electrophile = H₂O, D₂O, Me₃SiCl, t-BuCHO, Et₂CO, n-Pr₂CO, (CH₂)₅CO, Ph₂CO and adamantanone] at 0 °C yields the corresponding products 2, after hydrolysis with water. Cyclisation of some representative examples of compounds 2 with H₃PO₄ gives the corresponding dibenzoxepines 3.     

A one-pot synthetic approach to the functionalized isomeric ellipticine derivatives through an imino Diels-Alder reaction

An efficient, three component, one-pot synthesis of new isomeric ellipticine derivatives prepared through an imino Diels-Alder reaction of 3-aminocarbazoles and substituted benzaldehydes with electron-rich alkenes such as 3,4-dihydro-2H-pyran, 2,3- dihydrofuran and ethyl vinyl ether catalyzed by InCl₃ (10 mol %) in ionic liquid is reported. In the case of substituted benzaldehydes, reductive amination is observed.     

Gold(I)-catalyzed direct C-H arylation of pyrazine and pyridine with aryl bromides

An efficient procedure for the direct C-H arylation of electron-poor aromatics such as pyrazine and pyridine with aryl bomides is described. In the presence of catalytic amount of Cy₃PAuCl and with the use of t-BuOK as base, pyrazine undergoes the direct C-H arylation with aryl bromides at 100 °C, and the yields of the arylated products depend on the nature of aryl bromides. In the cases of electron-rich aryl bromides used, the arylated pyrazines can be obtained in good to high yields. For electron-poor aryl bromides, the addition of AgBF₄ is the crucial point to accelerate the coupling reaction to give the arylated products in moderate yields. Pyridine also reacts with electron-rich aryl bromides catalyzed by Cy₃PAuCl to give a mixture of arylated regioisomers in moderate yield. However, in order to realize the direct C-H arylation of pyridine with electron-poor aryl bromides, the addition of silver salt as additive and a milder reaction temperature (60 °C) are required.     

Extraction of arsenic compounds from lichens

Different extraction procedures were applied to improve the extraction efficiency of arsenic compounds from lichens. Two lichen species were chosen from an arsenic-contaminated environment: epiphytic Hypogymnia physodes (L.) Nyl. and terricolous Cladonia rei Schaer. Samples were extracted with water at temperatures of 20, 60 and 90 °C, using mixtures of methanol/water (9:1, 1:1 and 1:9), Tris buffer and acetone and the extracts speciated. Water and Tris buffer showed the best extraction efficiency of all extractants used; however, the extraction efficiency was still less than 23%. Since a major fraction of arsenic appeared to be associated with trapped soil particles, a sequential extraction procedure originally designed for soils (extraction steps: (1) 0.05 mol l⁻¹ (NH₄)₂SO₄; (2) 0.05 mol l⁻¹ (NH)₄H₂PO₄; (3) 0.2 mol l⁻¹ NH₄-oxalate buffer, pH 3.25; (4) mixture of 0.2 mol l⁻¹ NH₄-oxalate buffer and 0.1 mol l⁻¹ ascorbic acid, pH 3.25; (5) 0.5 mol l⁻¹ KOH) was applied and found to remove 45% of the total arsenic from H. physodes and 83% from C. rei. The lipid-soluble fraction of arsenic was estimated by k₀-INAA analysis of diethylether extracts and was found to be negligible. An HPLC-UV-HGAFS system was used to determine the arsenic compounds extracted. In both lichen species, arsenous acid, arsenic acid, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, trimethylarsine oxide and glycerol-ribose were detected. In addition, phosphate-ribose was found in H. physodes.