Oxidative entry to α-oxy N-acyl aminals and hemiaminals: efficient formation of 2-(N-acylaminal) substituted tetrahydropyrans

An efficient new method to synthesize α-oxy N-acyl aminals and hemiaminals in a single step from readily synthesized N-acyl enamines has been developed using PhI(OAc)₂ as the oxidant. The reaction conditions are very mild and the products are obtained in good yields (65-92%). A possible mechanistic pathway is laid out.     

Selective benzylic lithiation of N-Boc-2-phenylpiperidine and pyrrolidine: expedient synthesis of a 2,2-disubstituted piperidine NK1 antagonist

Unlike the lithiation of N-Boc-2-alkylpiperidines, which occurs at the 6-position, N-Boc-2-phenylpiperidine and N-Boc-2-phenylpyrrolidine can be lithiated exclusively at the 2-position. The tertiary carbanions can be trapped with a variety of electrophiles. This chemistry was used for the synthesis of a potent NK₁ ligand (K_i = 0.3 nM). The bioactive configuration at the piperidine quaternary center was determined by X-ray analysis to be (S).     

Free convection of a dusty‐gas flow along a semi‐infinite vertical cylinder

An analysis is performed to study the free convection of a dusty‐gas flow along a semi‐infinite isothermal vertical cylinder. The governing equations of the flow problem are transformed into non‐dimensional form and the resulting nonlinear, coupled parabolic partial differential equations have been solved numerically using an implicit finite difference scheme of Crank–Nicholson type. The flow variables such as gas–velocity, dust‐particle velocity and temperature, shearing stress and heat transfer coefficients are calculated numerically for various parameters occurring in the problem. It is observed that due to the presence of dust particles, the gas velocity is found to decrease. Copyright © 2009 John Wiley & Sons, Ltd.     

Metallocene-mediated cationic polymerization of vinyl ethers: Kinetics of polymerization and synthesis and characterization of statistical copolymers

The cationic polymerization of ethyl, n-butyl and iso-butyl vinyl ether, EVE, BVE and iBVE, respectively, was efficiently conducted using bis(η⁵-cyclopentadienyl)dimethyl hafnium, Cp₂HfMe₂, or bis(η⁵-cyclopentadienyl)dimethyl zirconium, Cp₂ZrMe₂ in combination with either tris(pentafluorophenyl)borate, B(C₆F₅)₃, or tetrakis(pentafluorophenyl)borate dimethylanilinum salt, [B(C₆F₅)₄]^?[Me₂NHPh]⁺, as initiation systems. The evolution of polymer yield, molecular weight and molecular weight distribution with time was examined. In addition, the influence of the initiating system, the monomer and the reaction conditions on the control of the polymerization was studied. Furthermore, statistical copolymers of EVE with BVE were prepared employing Cp₂HfMe₂ and [B(C₆F₅)₄]^?[Me₂NHPh]⁺ as the initiation system. The reactivity ratios were estimated using both linear graphical and non-linear methods. Structural parameters of the copolymers were obtained by calculating the dyad sequence fractions and the mean sequence length, which were derived using the monomer reactivity ratios. The glass transition temperatures, Tg, of the copolymers were measured by Differential Scanning Calorimetry, DSC, and the results were compared with predictions based on several theoretical models. The kinetics of thermal decomposition of the copolymers along with the respective homopolymers was studied by thermogravimetric analysis within the framework of the Ozawa-Flynn-Wall and Kissinger methodologies.     

The phytochemical analysis and antioxidant activity assessment of orange peel (Citrus sinensis) cultivated in Greece-Crete indicates a new commercial source of hesperidin

The flavonoid content of several methanolic extract fractions of Navel orange peel (flavedo and albedo of Citrus sinensis) cultivated in Crete (Greece) was first analysed phytochemically and then assessed for its antioxidant activity in vitro. The chemical structures of the constituents fractionated were originally determined by comparing their retention times and the obtained UV spectral data with the available bibliographic data and further verified by detailed LC-DAD-MS (ESI+) analysis. The main flavonoid groups found within the fractions examined were polymethoxylated flavones, O-glycosylated flavones, C-glycosylated flavones, O-glycosylated flavonols, O-glycosylated flavanones and phenolic acids along with their ester derivatives. In addition, the quantitative HPLC analysis confirmed that hesperidin is the major flavonoid glycoside found in the orange peel. Interestingly enough, its quantity at 48 mg/g of dry peel permits the commercial use of orange peel as a source for the production of hesperidin. The antioxidant activity of the orange peel methanolic extract fractions was evaluated by applying two complementary methodologies, DPPH(*) assay and the Co(II)/EDTA-induced luminol chemiluminescence approach. Overall, the results have shown that orange peel methanolic extracts possess moderate antioxidant activity as compared with the activity seen in tests where the corresponding aglycones, diosmetin and hesperetin were assessed in different ratios.     

Bifunctional coordination polymers as efficient catalysts for carbon dioxide conversion

The multidentate ligand H₂ L upon complexation with Zn (II) and Cd (II) provide a one‐dimensional polymeric networks. These coordination polymers (CPs) CP‐1 and CP‐2 containing Zn (II) and Cd (II) metals respectively are well characterized. The single crystal structural analysis confirms the formation of one‐dimensional coordination polymer with zigzag fashion in CP‐1 and ladder chain CP‐2 . Both the CPs are applied as catalysts to synthesize various cyclic carbonates from epoxides and carbon dioxide. The catalysts are giving better conversion under solvent‐free and additive‐free condition using 10 bar CO₂ and 100 °C as optimized pressure and temperature. The detailed kinetic experiments suggesting the first order kinetics, the energy of activation (Ea) is calculated for this catalytic conversion.     

Indirect electrochemical oxidation of substituted polycyclic aromatic hydrocarbons to corresponding para-quinones with potassium bromide in water–chloroform medium

Indirect electrochemical synthesis of quinone derivatives of a series of substituted anthracene and naphthalene by the electrolysis of aqueous solution of potassium bromide (3.0 M) using Pt anode at constant current density (40 mA/cm²) has been carried out. These reactions resulted in good to excellent yields of the corresponding para-quinones as confirmed by physical and spectral data.     

Highly efficient metal-free one-pot synthesis of α-aminophosphonates through reduction followed by Kabachnik–fields reaction using three-component system

One-pot synthesis of α-aminophosphonates directly from aryl nitro compounds, aldehydes/ketones, and diethyl phosphite using sodium dithionite through reduction and followed by Kabachnik–Fields reaction under metal-free conditions is reported. The major advantages are excellent yield, high chemoselectivity, neutral reaction medium, and simple experimental procedure. This methodology consists of the following steps: 1) amine formation from nitro compound, 2) imine formation from amine and aldehyde/ketone, 3) phosphate addition to imine.     

Formal [1,3] rearrangement of 2-furylmethyl and 2-thienylmethyl vinyl ethers

Benzyl and naphthylmethyl vinyl ethers are inert in LPDE medium, whereas hetcroaromntic methyl vinyl ethers, viz., 2-furyl and 2-thicnylmelhyl vinyl ethers undergo formal [1,3] rearrangement in LPDE medium.