Highly efficient and regioselective allylic amination of allylic alcohols catalyzed by [Mo3PdS4] cluster

A highly efficient and regioselective allylation reaction of amines with allylic alcohols under mild conditions catalyzed by the cubane-type sulfido cluster [(Cp∗Mo)₃S₄Pd(dba)][PF₆] with H₃BO₃ as an additive has been developed. A variety of amines and allylic alcohols are investigated, and in the case of allylic alcohols bearing substituents at either α- or γ-position only linear allylic amination products are obtained.     

SN2-Selective allylic substitution of chiral γ-aryl substituted allylic picolinates with alkynylcopper reagents

Substitution of γ-aryl secondary allylic picolinates with alkynyl copper reagents was studied. The copper reagent, prepared from TMSCCMgBr and CuBr·Me₂S in 2:1, was subjected to substitution of the picolinate derived from (E)-3-phenyl-1-methyl-2-propenyl alcohol at 0 °C for 1 h in THF to produce a mixture of α- and γ-products and the alcohol in 67:20:13, while the reagent in 3 or 4:1 ratio gave the α-product with 90-91% selectivity. On the contrary, reaction in CH₂Cl₂-THF (6-8:1) at 0 °C for 1 h furnished the α-product with 99% regioselectivity. The effect of CH₂Cl₂ was also demonstrated with eight more examples. Furthermore, 99% inversion was determined by transformation to the literature compound and by chiral HPLC.     

Regioselective synthesis of trifluoromethyl group substituted allylic amines via palladium-catalyzed allylic amination

The palladium-catalyzed regioselective allylic amination of α-trifluoromethylated allyl acetate occurred using Pd(OAc)₂/DPPE and [Pd(π-allyl)(cod)]BF₄/DPPF. The selective formation of the γ-product was attained by Pd(OAc)₂/DPPE, while the α-product was obtained using [Pd(π-allyl)(cod)]BF₄/DPPF.     

A highly α-regioselective In(OTf)3-catalyzed N-nucleophilic substitution of cyclic Baylis-Hillman adducts with aromatic amines

The highly α-regioselective N-nucleophilic substitution of B-H adducts bearing five (1a-f) or six-membered ring (5a-e) moieties with aromatic amines (2a-e) was developed under the catalysis of In(OTf)₃ (10 mol%). During the reaction the allylic rearrangement from γ-product to α-product occurred, resulting in thermodynamically stable α-product predominately.     

Anew technique for determining the adsorption energy of terminally adsorbed polymer

Using a new experimental technique, “Continuous Elution Method”, the desorption behavior of polystyrene(PS) and polystyrene (PS-X) functionalized by a terminal iminium ion (-X) from α-Al₂O₃ and γ-Al₂O₃ surface were investigated, and found that PS-X is forming a terminally adsorbed polymer layer on α-Al₂O₃, surface. Furthermore, it was found that the adsorption force of terminally adsorbed polymer is balanced with the desorption force which is contributed from the osmotic pressure in the adsorption layer. Based on this concept, the adsorption energy of the end-functionalized polystyrene terminally adsorbed on the α-Al₂O₃, surface was evaluated to be 4.2 ˜4.3 kT.     

New Approaches to the Use of Amino Acids as Chiral Building Blocks in Organic Synthesis [New Synthetic Methods (85)]

α-Amino acids protected at nitrogen in quite different ways can be transformed without racemization into the corresponding α-amino aldehydes. Provided one chooses the right protecting groups (e.g., two benzyl residues on nitrogen) it is possible for the first time to carry out Grignard-like, aldol, and Me₃SiCN additions, and hetero-Diels–Alder reactions with a high degree of nonchelation control. If the reactions of classical carbanions turn out to be nonselective, transmetalation, for example into organotitanium reagents, constitutes an important tool in controlling stereoselectivity. Diastereoselectivity can be reversed by specific variation of the protecting group and reagent. “Protecting-group tuning”, “metal tuning”, and “ligand tuning” are very useful in reactions of α-amino aldimines as well. The α-amino aldehydes can also be converted by Wittig reactions into electron-poor γ-amino olefins, which in turn undergo stereoselective cuprate, Michael, and cycloadditions.     

Titania and alumina ceramic membranes

This paper discusses the physical-chemical properties of γ-Al₂O₃ and TiO₂ ceramic membranes which have been prepared by sol-gel techniques from alkoxide starting materials. Mean pore size and pore size distributions are examined using N₂ sorption analysis. Particle size of sols as measured by in situ quasi-elastic light scattering is compared with SEM analysis of sintered membranes. Crack-free unsupported monoliths with thicknesses up to 120 μm have been prepared of γ-Al₂O₃. Supported TiO₂ membranes have been fabricated with thicknesses up to 0.5 μm. The γAl₂O₃ membranes are obtained from “particulate” sols, while for TiO₂ both “particulate” and “polymeric” sols have been used to produce membranes.     

gem-Difluoromethylation of α- and γ-ketoesters: preparation of gem-difluorinated α-hydroxyesters and γ-butyrolactones

PhSCF₂SiMe₃ has been demonstrated as difluoromethyl carbanion synthon (⁻CF₂H). It reacts chemoselectively with α- and γ-ketoesters at the keto group in the presence of a catalytic amount of TBAF in THF to give the corresponding α-hydroxy ester adducts as well as γ-gem-difluorophenylsulfanylmethylated-γ-butyrolactones in good yields. Reductive cleavage of the phenylsulfanyl group of these products employing Bu₃SnH/AIBN gives the corresponding gem-difluoromethylated α-hydroxyesters and γ-butyrolactones in good yields.     

Structure and phase transitions in poly(diethylsiloxane)

The structure changes accompanying phase transitions in poly(diethylsiloxane) (PDES) have been studied by WAXS and SAXS techniques using oriented and isotropic samples. PDES may exist in two low-temperature modifications (the monoclinic α₁-form and presumably the “tetragonal” β₁-form) and two high-temperature modifications (the monoclinic α₂-form and the “tetragonal” β₂-form). In linear PDES the crystal - crystal transitions α₁–α₂ and β₁–β₂ occur near 214 and 206 K, respectively. At higher temperatures α₂ (280 K) and β₂ (290 K) forms transform into the mesomorphic phase α_m that gradually melts at 280–300 K giving an amorphous phase. According to x-ray and density data, α_m phase is also characterized by monoclinic structure slightly different from hexagonal packing.     

Formation and phase transition of cobalt molybdate in cobalt oxide-molybdenum trioxide-alumina system

In the cobalt oxide-molybdenum trioxide-alumina system with a molar ratio of 1:1:1, the amounts of the high-temperature modification (a) of CoMoO₄ formed during heating from 500 to 800°C and the low-temperature modification (b) formed by phase transition during the subsequent cooling to room temperature are influenced by the kinds of alumina used, such as α-, γ- and calcined γ-aluminas. Powder X-ray diffraction analysis revealed that in an α-alumina system formation of a-CoMoO₄ is most favorable at a calcination temperature of 500°C and phase transition from a- to b-CoMoO₄ during cooling is enhanced by higher calcination temperatures. In the γ-alumina system, formation of a-CoMoO₄ is slight at 500°C but increases with increase in the calcination temperature, as does slightly the degree of phase transition from a- to b-CoMoO₄ upon cooling. In a system containing calcined γ-alumina, formation of a-CoMoO₄ similar to α- and γ-alumina systems was observed to occur at 500°C and 800°C, respectively, together with phase transition to b-CoMoO₄ during cooling. The degree of dispersion in the CoOMoO₃ coexistent system is affected by the particle size of aluminas, such as coarse α-, fine amorphous γ- and calcined γ-alumina consisting of both sizes, as observed with electron microscopy. Presence of finer γ-alumina is considered to suppress or retard the solid state reaction and phase transition.     

Reaction of aldehydes and ketones with t-butyl bromide-dimethyl sulphoxide

Reacting aldehydes and ketones with the “Bu^tBr-Me₂SO” system produces the corresponding α-bromoderivatives $\text{2}$. In the case of ketones, is possible, bromination is obtained exclusively at the more highly substituted α-position. With slight modifications of the reaction conditions (add to obtain “in situ” formation of either dimethyl(2-oxo-2-phenylalkyl)sulphonium salts $\text{3}$ or of α-methylthioderivatives $\text{4}$. Dimethyl(l-m bromide ($\text{3h}$) during crystallization undergoes spontaneous resolution of the two enantiomers, as demonstrated by single crystal X-ray analysis a     

Reactivity of η-, γ-, and α-Al2O3 for ZnAl2O4 Formation

The rate of ZnAl₂O₄ formation was measured for η-, γ-; and α- Al₂O₃ in order to distinguish the reactivity of them. The reactivity decreased as follows: η- > γ- > α-Al₂O₃. The reaction rate fitted to Jander's equation and the activation energies calculated were 33, 47 and 113 Kcal/mol for η-, γ- and α-Al₂O₃ systems, respectively. These differences are explained by an assumption that η- and γ-Al₂O₃ resulted in a ZnAl₂O₄ with imperfect spinel structure, but α-Al₂O₃ gave the perfect spinel structure. This assumption is based on the theoretical consideration of the activation energy needed for the diffusion-controlled reaction and date of lattice constant of each ZnAl₂O₄ obtained from three aluminas. The fact that η-Al₂O₃ shows very high reactivity compared with that of γ-Al₂O₃ was found to be explained on the basis of Jander's equation, a comparison of specific surface area and the defect structures of the aluminas.     

The energy parameters of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane polymorphs and their phase transitions

The calculated dispersion and electrostatic intermolecular interaction energies in crystals of γ, α(H₂O), and ? polymorphs of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazawurtzitane (HNIW) were compared. Preliminarily, nonempirical quantum-chemical calculations of the three compounds with complete geometry optimization were performed using the GAUSSIAN-03 package and density functional theory. The dispersion intermolecular interaction energy was calculated with the “6-exp” potential. The van der Waals and dipole-dipole interaction energies were substantially different in crystals of different HNIW polymorphs, but total energy changes in phase transitions were close to zero. The calculated ? > γ and α(H₂O) > γ phase transition energies were close to the experimental values determined using a differential calorimeter. Dehydration substantially influenced the kinetics and heat effects of polymorphic transitions.     

Cs2CO3-promoted synthesis of p-terphenyls from allyl ketones

An efficient Cs₂CO₃-promoted synthesis of acylated p-terphenyls from allylic ketones under mild conditions has been developed. The reaction occurred in moderate to good yields and tolerated γ-aryl substituted allylic aryl ketones containing functionalities such as alkanes, ethers and halogens.     

Analysis of exact valence shell hamiltonian: Nonclassical terms and molecular based parameters

The exact valence shell effective hamiltonian is analyzed for one- and two-valence orbital systems using a second quantized formulation. The exact solutions of the exact effective hamiltonian are used, to display the meaning of each of its terms. The well-known α_υ = ?I_p and γ_υυ = I_p ? A_f relations are provided a molecular basis for certain special cases, thereby enabling molecular definitions for molecular “integrals” and allowing the determination of the molecule and bond length dependence of traditional semi-empirical “integrals”. It is shown how the presence of nonclassical terms in the effective hamiltonian destroys the pairing symmetry of alternate hydrocarbons.     

Fourier-transform infrared studies of polypropylene during mechanical deformation

Quantitative Fourier-transform infrared (FTIR) measurements of frequency shifts Δν and absorbance profile asymmetry are reported for various polypropylene samples as a function of uniaxial stress σ. Generally, it was found that the frequency shift coefficient α_χ, defined by Δν = α_χσ, depended on stress rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, draw ratio, λ, molecular orientation f, tensile modulus E, and annealing conditions. With annealing, α_χ decreased with increasing shrinkage in the case of highly oriented isotactic PP. The α_χ values for the “helix bands” were less affected than those for the “liquid bands.” With increasing \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, generally α_χ increased to an apparent asymptotic limit. With increasing λ, f, or E, α_χ also increased from α_χ ? 0 for λ = 1 (spherulitic) to maximum values for highly oriented isotactic PP. The observed variations in α_χ can be interpreted in terms of the changes in the peak position and shape of the nonuniform molecular stress distribution. Analogous behavior with x-ray diffraction peaks obtained for polymers under stress is discussed.     

The Molecular Dynamic Simulation of Zolpidem Interaction with Gamma Aminobutyric Acid Type A Receptor

Our goal was to generate the extracellular domain of gamma‐aminobutyric acid type A receptor (GABA_A receptor) by comparative modeling and to study the interaction of zolpidem with the GABA_A receptor. The modeling strategy was verified to provide reasonable 3‐dimensional coordinates. These coordinates helped to combine all the subunits well. The benzodiazepine (BZ) binding site was located in a binding pocket between the α₁ and γ₂ subunits of the GABA_A receptor. Zolpidem was selected to dock into the binding site. In our study, the residues of the binding pocket were suggested to be αHis129, αTyr187, αGly228, αThr234, αTyr237, γMet96, γPhe116, γSer130, γGly143, and γMet169. By the calculation of the docking module, the conformation of zolpidem docking in the BZ binding site was investigated. A hydrogen bond was found at γArg136 when zolpidem's conformation was in rank 2 of the docking score. The contracted binding pocket showed residues at αHis129, αTyr187, αGly228, αTyr237, γPhe116, and γMet169. Zolpidem docking in a contracted binding pocket might generate a hydrogen bond in α His 129.     

Synthesis and reactions of sulfur-substituted α,β-unsaturated δ- and γ-lactones

A new synthetic method for the preparation of sulfur-substituted α,β-unsaturated δ- and γ-lactones has been developed by reaction of the allylic bromides of 5,6-dihydro-2-pyridinones with NaOH in refluxing MeOH or t-BuOH. The substituents at C5 and C6 of these substrates are very important for the success of this reaction. Some synthetic transformations of the α,β-unsaturated δ-lactones have also been carried out.     

Density functional calculations on cyclodextrins

Conformations of α-, β-, and γ-CDs under anhydrous conditions in the gas phase were investigated by a density functional method, B3LYP/6-31G(d,p). These calculations resulted in several symmetric conformations with different energies. The lowest energy conformations contain two rings of homodromic hydrogen bonds and are referred to “one-gate-closed” conformations. Different orientations of hydrogen bonds lead to four minima. Other conformational minima were found for “open” conformations which correspond to some extent to experimentally determined structures.