Solving 2D time‐fractional diffusion equations by a pseudospectral method and Mittag‐Leffler function evaluation

Two‐dimensional time‐fractional diffusion equations with given initial condition and homogeneous Dirichlet boundary conditions in a bounded domain are considered. A semidiscrete approximation scheme based on the pseudospectral method to the time‐fractional diffusion equation leads to a system of ordinary fractional differential equations. To preserve the high accuracy of the spectral approximation, an approach based on the evaluation of the Mittag‐Leffler function on matrix arguments is used for the integration along the time variable. Some examples along with numerical experiments illustrate the effectiveness of the proposed approach. Copyright © 2016 John Wiley & Sons, Ltd.     

Solvent‐Dependent Enantiodivergence in the Chlorocyclization of Unsaturated Carbamates

A remarkable solvent‐controlled enantiodivergence is seen in the hydroquinidine 1,4‐phthalazinediyl diether ((DHQD)₂PHAL)‐catalyzed chlorocyclization of unsaturated carbamates. Eyring plot analyses of this previously unreported reaction are used to probe and compare the R‐ and S‐selective pathways. In the CHCl₃/hexanes solvent system, the pro‐R process shows a surprising increase in selectivity with increasing temperature. These studies point to a strongly solvent‐dependent entropy–enthalpy balance between the pro‐R and pro‐S pathways.     

Ionic Liquid Promoted Efficient Three-Component Synthesis of 2-Thioxo-2H-Thiopyrans

Abstract

An efficient one-pot three-component method for the synthesis of a variety of 2-thioxo-2H-thiopyrans has been described. Fairly good yields are obtained by cyclization reactions of arylidenemalononitriles, derived in situ from ketones and malononitrile, with carbon disulfide in the presence of a base in the ionic liquid 1-butyl-3-methylimidazolium bromide as reaction medium.

[Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Selected Data.]

GRAPHICAL ABSTRACT      

Inhibition of acid‐induced decomposition of diphenyltriazenes by complexation with cyclodextrins

Acid‐promoted N? N bond cleavage in 1,3‐diphenyltriazenes (X‐Ph‐N=N‐NH‐Ph‐X; X = H, 4‐OCH₃), leading to formation of diazonium ions and anilines, is strongly inhibited in aqueous solutions in the presence of cyclodextrins (CDs). The inhibition is ascribed to the formation of inclusion complexes that render the guest diphenyltriazene significantly less basic as a result of the less polar nature of the CD cavity (a microsolvent effect). Association equilibrium constants for 1:1 host–guest complexes increase in the order α‐CD <β‐CD ～ permethyl‐β‐CD < hydroxypropyl‐β‐CD, with values for X = 4‐OCH₃ being larger than those for X = H. In the case of α‐CD, formation of 2:1 host–guest complexes is also involved. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 567–574, 2010     

Synthesis and Theoretical Study of Intramolecular Hydrogen Bond at Two Possible Positions in Pyrazolo[1,2‐b]phthalazine

Properties of dimethyl 3‐(alkylamino)‐5,10‐dioxo‐5,10‐dihydro‐1H‐pyrazolo[1,2‐b]phthalazine‐1,2‐dicarboxylate and its derivatives were studied by means of ab initio method. NO₂ derivative of title compound was synthesized and the nature of its intramolecular hydrogen bond (HB) was investigated. Furthermore, the topological properties of the electron density distributions for N? H···O intramolecular bridges were analyzed in terms of the Bader theory of atoms in molecules (AIM). The electron density (ρ) and Laplacian (?²ρ) properties, estimated by AIM calculations, indicated that O···H bond possesses low ρ and positive ?²ρ values which are in agreement with electrostatic character of the HBs, whereas N? H bonds have covalent character (?²ρ<0). Moreover, steric effect of the t‐Bu group on structure and topological parameters of pyrazolo[1,2‐b]phthalazine conformers was studied. Finally, the powerful method of Espinosa was used to obtain the H‐bond energy.     

Three-component reactions of isocyanides, dialkyl acetylenedicarboxylates, and trans-cinnamoyl chlorides for the synthesis of highly functionalized 2-vinyl furans

Abstract  

In this study, we present a convenient and efficient method for the synthesis of novel, highly substituted 2-vinyl furans using a three-component reaction. The zwitterions generated from the reaction of isocyanides and dialkyl acetylenedicarboxylates are reacted with trans-cinnamoyl chlorides to produce the desired products in good yields.     

Diastereoselective synthesis of 5-iminooxazolines and their subsequent transformation to α,α-disubstituted dipeptide esters: a formal [4+1] cycloaddition reaction of cyclohexyl isocyanide and Z-alkyl-α-benzoyl amino-acrylates

A novel atom economical diastereoselective synthesis of 5-iminooxazolines and their subsequent transformation to α,α-disubstituted dipeptide esters is described. Heating a mixture of cyclohexyl isocyanide and Z-α-benzoyl amino-acrylic acid alkyl esters under solvent-free conditions, afforded 5-iminooxazolines, which, upon specifications provided α,α-disubstituted dipeptide esters in good yield.     

A lupane triterpenoid and other constituents of Salvia eremophila

Phytochemical investigation of the aerial parts of Salvia eremophila led to the isolation of a lupane triterpenoid, 3β, 20-dihydroxylupane-28-oic acid (1), together with eight other compounds, comprising three diterpene, two triterpene, two flavonoids and a steroidal glucoside. Their structures were elucidated by interpretation of their one-dimensional and two-dimensional NMR spectra and completed by the analysis of the HRESIMS data. Compounds 1, 2-4 and 8 were evaluated for their cytotoxicities against five human tumour cell lines. Compounds 1 and 3 hold a good potential for use in future studies due to their anti-cancer properties.     

Diastereoselective synthesis of highly functionalized quinolizines via a pyridine-based three-component reaction and a DFT investigation on the reaction mechanism

Novel, one-pot, three-component reactions of the zwitterions generated in situ from pyridine and acetylenic esters with alkoxymethylenemalononitriles via 1,4-dipolar cycloadditions are described. The reactions afforded dialkyl 1,1-dicyano-2-alkoxy-1,9a-dihydro-2H-quinolizine-3,4-dicarboxylate derivatives in good to high yields without using any catalyst or activation. Structural, electronic, energetic, and mechanistic details of the reaction are also revealed by density functional theory (DFT) calculations, which strongly support the exclusive formation of the observed products.     

Thermomechanical coupling of geometrically non-coherent interfaces

An evacuated tube collector is composed of a vacuum glass tube forged to a metal tube creating an interface which undergoes thermomechanical cyclic loading. To numerically model such a thermomechanical and geometrically non-coherent interface, a decohesion element with mixed-mode capability, based on a normal-shear decomposition of the displacement discontinuity vector is used, exploiting exponential traction-separation laws. In addition to the classical strategies, interfacial elements are allowed to have an in-plane stretch resistance by assuming a thermohyperelastic interface Helmholtz energy, a function of the rank-deficient interface deformation gradient and temperature , as an extension of the surface/interface elasticity theory. The nonlinear governing equations are given and solved using the finite element method. The results are illustrated through a series of numerical examples for different material parameters. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)