Wolff rearrangement of alpha-diazoketones using in situ generated silver nanoclusters as electron mediators

[reaction: see text] We report Wolff rearrangement of alpha-diazoketones by in situ generated silver nanoclusters (Ag(n)(), 2-4 nm) from silver(I) oxide (Ag(2)O) involving a nonclassical electron-transfer process. Our results show that Ag(n)()(+)/Ag(n)()(0) redox couple allows the initial removal of an electron from alpha-diazoketone and its back-donation after chemical reaction(s). Controlled potential coulometry (CPC) of various alpha-diazoketones results in the realization of Wolff-rearranged carboxylic acids in excellent yields.     

A short and efficient asymmetric synthesis of (−)-frontalin, (−)-exo-isobrevicomin and a volatile contributor of beer-aroma

The natural products, (−)-frontalin and (+)-exo-isobrevicomin were synthesized employing Sharpless asymmetric epoxidation and ZrCl₄-catalyzed intramolecular acetalization as the key steps. (−)-Frontalin was synthesized in three steps with a 61.4% overall yield and 89.9% ee and (−)-exo-isobrevicomin also obtained in an overall satisfactory yield of 10.1% and 97% ee. We have also synthesized the volatile contributor of beer aroma in a 96% ee.     

Structural properties and magnetic interactions in Al3+ and Cr3+ co-substituted CoFe2O4 ferrite

A series of CoAl_xCr_xFe_2−2xO₄ systems (x = 0.1 to 0.5 in steps of x = 0.1) spinel ferrites have been synthesized successfully using wet chemical co-precipitation technique. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and magnetization measurements. The powder XRD patterns confirm the single phase spinel structure for the materials synthesized. X -ray diffraction measurements were performed to yield the lattice constant as function of the amount x corresponding to Al-Cr substitution. Lattice parameters, X-ray density, bulk density and particle size decrease whereas porosity increases with the increase in Al-Cr content, ‘x’. Infrared studies show two absorption bands at about 400 cm⁻¹ and 600 cm⁻¹ for octahedral and tetrahedral sites, respectively. Saturation magnetization decreases with the increase in Al-Cr content x. AC magnetic susceptibility measurements were carried out as a function of temperature to measure the Curie temperature, which was found to decrease with Al-Cr content x. The decrease of Curie temperature has been explained by A-B interaction.      

Sorption behavior of metal ions on thiourea-impregnated silica gel G and alumina stationary phases in aqueous HCl and acetone—HCl media: Quantitative separation of Pb2+ and Hg2+ from other metal ions

JPC – Journal of Planar Chromatography – Modern TLC - The sorption behavior of a number of metal ions was investigated on thiourea-impregnated silica gel G and alumina layers with...     

Highly selective oxidative cleavage of beta-cyclodextrin-epoxide/aziridine complexes with IBX in water

Water, an environmentally friendly reaction medium, has been utilized for the reaction of IBX with various epoxides 1 and aziridines 2 as their beta-cyclodextrin complexes to afford for the first time alpha-hydroxyketones 3 and alpha-aminoketones 4, respectively.     

Highly regioselective ring opening of oxiranes with phenoxides in the presence of beta-cyclodextrin in water

Highly regioselective ring opening of oxiranes to beta-hydroxy ethers with phenoxides has been achieved in impressive yields in the presence of beta-cyclodextrin as catalyst and water as solvent.     

Development and Validation of Catalytic Kinetic Spectrophotometric Method for Determination of Copper(II)

A catalytic kinetic spectrophotometric method is developed for the determination of trace amounts of Cu(II). It is based on the catalytic effect of Cu(II) on the oxidation of cysteine (RSH) by hexacyanoferrate(III) in acidic medium. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of hexacyanoferrate(III) at 420nm. The optimum operating conditions regarding concentration of reagents, pH and temperature were established. The working curve is linear in the concentration range of 0–6.35ng·mL^–1. The maximum percentage error and standard deviation for determination of Cu(II) in the range of 1.27–6.35ng·mL^–1 have been calculated to be 3.9 and 0.4 respectively. The detection limit calculated was 0.15ng·mL^–1. The interference effect of several species was also investigated, and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cu(II) in various synthetic and real samples. The typical feature of this procedure is that determination can be carried out at 25°C and/or in the absence of any precision thermostatic bath in the very short analysis time of one minute. The newly developed method was found to have fairly good selectivity, sensitivity, simplicity and rapidity compared to other kinetic methods.Received October 8, 2002; accepted April 7, 2003 Published online July 16, 2003     

Asymmetric aziridination with chiral allyl aminosulfoxonium ylides: synthesis of alkenyl aziridine carboxylates and palladium-catalyzed E,trans/E,cis-isomerization of an alkenyl aziridine

Chiral cyclic and acyclic allyl aminosulfoxonium ylides have been generated from aminosulfoxonium-substituted β,γ-unsaturated α-amino acids (method A) and 1-alkenyl aminosulfoxonium salts (method B) upon treatment with DBU. Their application to the asymmetric aziridination of N-tert-butyl-sulfonyl imino ester, generated either in situ (method A) or externally added (method B), gave the corresponding alkenyl aziridine carboxylates with medium to high diastereoselectivity and enantioselectivity. A highly stereoselective Pd(0)-catalyzed isomerization of an E,trans-configured alkenyl aziridine methanol derivative to its E-cis-isomer is described, which proceeded with retention of the double bond configuration.     

An industrially viable catalyst system for palladium-catalyzed telomerizations of 1,3-butadiene with alcohols

The telomerization reaction of 1,3-butadiene with alcohols to give alkyl octadienyl ethers in the presence of palladium-carbene catalysts has been studied in detail. Unprecedented catalyst efficiency with turnover numbers (TON) up to 1,500,000 and turnover frequencies (TOF) up to 100,000 h(-1) have been obtained after optimization for the reaction of methanol in the presence of an excess of in situ generated carbene ligands. High yields (75-97 %) and catalyst productivities (TON 15,000-100,000) are observed for other aliphatic alcohols and phenols. For comparison five carbene-palladium(0) complexes have been synthesized and characterized by X-ray crystallography. Both electronic and steric effects on the stability and reactivity of the catalysts have been discussed on the basis of density functional theory calculations.     

Synthesis of poly(thio-1,4-phenylene) by oxidative coupling reaction of diphenyl disulfide with potassium persulfate in strongly acidic solutions

The synthesis of poly(thio- 1,4-phenylene) (PPS) at room temperature by the reaction of diphenyl disulfide with potassium persulfate (K₂S₂O₈) in non-basic solvents, in the presence of trifluoromethanesulfonic acid, is reported. The reaction in chlorinated solvents, such as dichloromethane and tetrachloroethane, resulted in partial oxidation of sulfide to sulfoxide and sulfone. On the other hand, the polymerization proceeded well in nitrobenzene and the PPS formed was free of branches, crosslinks and thianthrene units. The molecular weight of the polymers formed in different solvents were in the range 2000–8000. The reaction proceeded under identical conditions with bis(2,6-dimethylphenyl) disulfide as well, but the polymer yield was lower.