Palladium(II) acetate‐catalyzed reduction of imines to the corresponding amines by triethylsilane

Reduction of a variety of imine compounds with triethylsilane in the presence of catalytic amounts of palladium(II) acetate in ethanol resulted in the formation of the corresponding amines in excellent yields after short reaction times. Copyright © 2013 John Wiley & Sons, Ltd.     

An experimental and theoretical investigation of the regio- and stereoselectivity of the polar [3+2] cycloaddition of azomethine ylides to nitrostyrenes

The regio- and stereochemical polar [3+2] cycloaddition of the azomethine ylides, which were generated in situ by the reaction of isatin derivatives and proline, with trans-β-nitrostyrene and (E)-1-phenyl-2-nitropropene were studied using experimental and theoretical methods. In comparison with trans-β-nitrostyrene, when the reactions were performed with (E)-1-phenyl-2-nitropropene, a remarkable inversion in the regioselectively was observed. The regioselectivity of the reactions was investigated using global and local reactivity indices and frontier molecular orbital (FMO) analysis at the B3LYP/6-31G(d,p) level of theory. The effects of the electronic and steric factors on the regioselectivity of the reactions were discussed. The inspection of geometries and energetics of transition states revealed the importance of weak interactions in regioselectivity of the cycloaddition reactions.     

Effect of Side Chains on Charge Transfer in Quaterthiophene-Naphthalene Diimide Based Donor-Bridge-Acceptor Dyads

We have probed the effect of side chains on the charge transfer dynamics in dyads containing quaterthiophene (QT) donor and naphthalene diimide (NDI) acceptor. The donor and the acceptor are covalently linked using a flexible linker. Four dyads (1–4) were synthesized with the quaterthiophene bearing hexyl side chain and the naphthalene diimide bearing hydrocarbon, fluorocarbon, branched or polar side chains. The UV-Vis spectra for these dyads showed the existence of a donor-acceptor complex. The time-resolved fluorescence (TRF) decay studies show a rapid quenching of fluorescence in all the dyads upon excitation of the donor. We found that the side chains on the NDI did not alter the quenching rates in solution.     

Me3SiCl and Et3SiI‐promoted one‐pot synthesis of 1,4‐dihydropyridine derivatives

An efficient synthesis of 1,4‐dihydropyridine derivatives has been achieved by the one‐pot cyclocondensation reaction of methyl 3‐aminocrotonate and a range of aldehydes in the presence of chlorotrimethylsilane as a promoter under solvent‐free conditions. The cyclocondenstion reaction requires a very short time and takes place in good to excellent yields. Furthermore iodotriethylsilane, generated in situ by the reaction of triethylsilane and methyl iodide in the presence of palladium chloride, has been investigated for the synthesis of 1,4‐dihydropyridine derivatives. This facile and efficient method affords high yields for the preparation of 1,4‐dihydropyridines at room temperature and short reaction times. Copyright © 2009 John Wiley & Sons, Ltd.     

Palladium‐catalyzed reduction of nitroaromatic compounds to the corresponding anilines

Reduction of a variety of nitroaromatic compounds with triethylsilane in the presence of catalytic amounts of palladium chloride in ethanol resulted in the formation of the corresponding anilines in excellent yields. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of inclusion complex formation between a cationic surfactant, two cyclodextrins and a drug

In this study inclusion of hexadecyltrimethylammonium bromide (HTAB) with α-, and β-cyclodextrin (CD) in the presence and the absence of bromhexine (BH) was investigated using ion-selective electrode method. The association constants of HTAB with CDs were determined by potentiometry and were close to literature values. The obtained results indicated that α-CD formed 1:1 and 1:2 inclusion complexes, but β-CD formed only a 1:1 inclusion complex. In the presence of drug, the interaction between CDs and HTAB decreased, because both drug and HTAB could interact with CDs. The results showed that the interaction between drug and CDs are greater than HTAB and CDs. The stoichiometry of the inclusion complexes, the critical aggregation concentration (CAC), the monomer surfactant concentration of HTAB, [HTAB]_f, and also the effect of the inclusion complex on the micellization process of the HTAB were determined by conductivity measurements.     

Casimir energy–momentum tensor for curved boundaries in de Sitter space-time

In the present paper, we study Casimir effect for a conformally coupled scalar field propagating on background of \(4+1\)-dimensional de Sitter (dS) space-time. The field is supposed to obey Dirichlet boundary condition on two 4-dimensional curved boundaries. Technically, we accomplish our calculations using an indefinite field quantization scheme, which already has been successfully applied to the dS minimally coupled massless scalar field and the dS linear gravity to obtain a causal and fully covariant quantum field on dS space-time.     

A complexation study of 15-crown-5 with Co2+ cation in some pure and mixed organic solvents

The stability constant (log K _f) and the thermodynamic parameters (free energies, enthalpies, and entropies) of the complexation of Co²⁺ cation with 15-crown-5 (15C5) in acetonitrile-methanol (AN/MeOH), acetonitrile-nitrobenzene (AN/NB), acetonitrile-dichloromethane (AN/DCM) and acetonitrile-1,2-dichloroethane (AN/DCE) binary solvent solutions were calculated from the experimental conductance data at different temperatures. The complexation behavior of the crown ether used in these media was discussed in view of the estimated parameters. In all solvent systems, 15-crown-5 formed a 1: 1 complex with Co²⁺ cation. The stability order of (Co-15C5)²⁺ complex in the binary mixed solvents at 25°C was found to be: AN/NB > AN/DCM ≈ AN/DCE > AN/MeOH. In most cases, a non-linear relationship was observed for changes of log K _f of (Co-15C5)²⁺ complex versus the composition of the binary mixed solvent systems. The experimental results show that the standard thermodynamic parameters of the complexation process change with the nature and composition of the binary solvent solutions.