Intramolecular nitrone cycloaddition reaction on carbohydrate-based precursors: application in the synthesis of spironucleosides and spirobisnucleosides

A simple synthesis of chiral spironucleosides and spirobisnucleosides is described. Intramolecular 1,3-dipolar nitrone cycloaddition reaction of d-glucose-derived precursors having olefin at C-3 and nitrone at C-5, C-1, or C-2 (in nor-series) furnished bisisoxazolidinospirocycles 4-7, 11, and 12 in good yields. Reductive ring opening of the isoxazolidine moieties in 4-6 followed by construction of a nucleoside base upon the generated amino groups smoothly yielded spirobisnucleosides 17 and 18 and spironucleosides 20 and 21.     

Processable heat-resistant polymers. XI. Synthesis and characterization of unsaturated polyamideimides

Polycondensation of the diacid chloride of 2-(3-carboxy vinyl)phenyl-1,3-dioxoisoindoline-5-carboxylic acid with m-phenylenediamine and the diacid chloride of 2-(4-carboxy phenyl)-1,3-dioxoisoindoline-5-carboxylic acid with 1,5-bis(3-aminophenyl)1,4-pentadien-3-one was carried out in polar solvents to produce new unsaturated polyamide–imides. The solution and the thermal, electrical, and a few other properties of the polymers were studies. The polymers were soluble in highly polar solvents. The solubility parameter of the polymers was calculated from the Small's group contribution. The polymers were fairly thermostable and underwent crosslinking creaction when heated, preferably in the presence of a suitable catalyst. The crosslinked polymers were in soluble even in highly polar solvents and possessed higher thermal stability. The swelling behavior of the polymers was studied and the molecular weight between two consecutive crosslinks was determined. X-ray diffraction and the dielectric properties of the polymers and their crosslinked products were also studied.     

More Efficient Palladium Catalyst for Hydrogenolysis of Benzyl Groups

Organic halides absorbed without solvent onto sodium phenylsulfinate on alumina (1) gave phenylsulfones (2) under microwave or ultrasound activation.     

Grafting Vinyl Monomers onto Poly(ethylene Terephthalate) (PET). IV. Graft Copolymerization of Methyl Methacrylate onto PET Fibers Using Acetyl Acetonate Complexes of Mn(III), Co(III), and Fe(III)

The graft copolymerization of methyl methacrylate onto poly-(ethylene terephthalate) using metal complexes of Mn³⁺, Co³⁺, and Fe³⁺ as initiators was studied. The rate of polymerization, R_p, increased with increasing complex concentrations.

The rate of polymerization was also studied by varying monomer concentrations. Increasing monomer concentrations, the rate of polymerization increases significantly. The graft yield increases with increasing temperature within the range 60–75°C. The graft yield is medium dependent. A suitable kinetic scheme has been pictured and rate equations have been derived.     

Thermodynamic investigations of uranium-rich binary and ternary alloys

Uranium–zirconium, uranium niobium, and uranium–zirconium–niobium alloys were synthesized by the arc melting technique and their phase transition temperatures were determined using a high temperature calorimeter. Heat capacities of U–7 wt%Zr, U–7 wt%Nb, U–5 wt%Zr–2 wt%Nb, U–3.5 wt%Nb–3.5 wt%Zr, and U–2 wt%Zr–5 wt%Nb were measured using a differential scanning calorimeter in the temperature range 303–921 K. A set of self-consistent thermodynamic functions such as entropy, enthalpy, and Gibbs energy function data for these binary and ternary alloys were reported for the first time using heat capacity data obtained in this study and required literature data.     

A Facile One‐Pot Synthesis of Pyrrolo[1, 2‐a] Indoles by Intramolecular 1,3‐Dipolar Cycloaddition under Neat‐Microwave Irradiation

A straightforward and general approach for the stereoselective synthesis of fused pyrrolo[1,2‐a] indoles frameworks from>intramolecular 1,3‐dipolar cycloaddition using N‐alkylated Baylis–Hillman derivatives is presented. It was found that the cycloaddition proceeded efficiently under microwave irradiation in solvent‐free condition to afford highly stereoselective cycloadducts in good yield.     

Linear {NiII–LnIII–NiII} Complexes Containing Twisted Planar Ni(μ‐phenolate)2Ln Fragments: Synthesis,Structure, and Magnetothermal Properties

Sequential reaction of a multisite LH₄ ligand {2‐[2‐hydroxy‐3‐(hydroxymethyl)‐5‐methylbenzylideneamino]‐2‐methylpropane‐1,3‐diol} with appropriate lanthanide salts followed by the addition of Ni(NO₃)₂ ? 6 H₂O in a 4:1:2 stoichiometric ratio in the presence of triethylamine afforded four heterobimetallic trinuclear complexes [Ni₂Gd(LH₃)₄] ? 3 NO₃ ? 3 MeOH ? H₂O ? CH₃CN ( 1 ), [Ni₂Tb(LH₃)₄] ? 3 NO₃ ? 3 MeOH ? CH₃CN ( 2 ), [Ni₂Dy(LH₃)₄] ? 3 NO₃ ? 3 MeOH ? H₂O ? CH₃CN ( 3 ), and [Ni₂Ho(LH₃)₄] ? 3 NO₃ ? 3 MeOH ? H₂O ? CH₃CN ( 4 ). Complexes 1 – 4 possess linear trimetallic cores with a central lanthanide ion. Magnetic studies revealed a predominant ferromagnetic interaction between the Ni and Ln centers. Alternating current susceptibility measurements of complex 3 showed a small frequency dependence of the out‐of‐phase signal, χ′′_M , under zero direct current field, but without achieving a net maximum above 2 K. Magnetic studies on 1 revealed that it has a significant magnetocaloric effect.     

Influence of magnetic quantization on the effective electron mass in Kane-type semiconductors

Summary We study the effective electron mass at the Fermi level in Kane-type semiconductors on the basis of fourth order in effective mass theory and taking into account the interactions of the conduction electrons, heavy holes, light holes and split-off holes, respectively. The results obtained are then compared to those derived on the basis of the well-known three-band Kane model. It is found, takingn-Hg_1−x Cd _x Te as an example, that the effective electron mass at the Fermi level in accordance with fourth-order model depends on the Fermi energy, magnetic quantum number and the electron spin respectively due to the influence of band nonparabolicity only. The dependence of effective mass on electron spin is due to spin-orbit splitting parameter of the valence band in three-band Kane model and the Fermi energy due to band nonparabolicity in two-band Kane model. The same mass exhibits an oscillatory magnetic-field dependence for all the band models as expected since the origin of oscillations in the effective mass in nonparabolic compounds is the same as that of the Shubnikov-de Hass oscillations. In addition, the corresponding results for parabolic energy bands have been obtained from the generalized expressions under certain limiting conditions.