Kinetic Resolution and Dynamic Kinetic Resolution of Chromene by Rhodium‐Catalyzed Asymmetric Hydroarylation

A highly efficient kinetic resolution and dynamic kinetic resolution of chromene is reported for the first time and they procced by a rhodium‐catalyzed asymmetric hydroarylation pathway. This new approach offers versatile access to various chiral 2,3‐diaryl‐chromanes containing vicinal stereogenic centers, as well as the recovered chiral flavenes, in high yields with excellent ee values (s factor up to 532). Particularly noteworthy is that this strategy can be further extended to the establishment of a dynamic version of the kinetic resolution of chromene acetals and allows complete access to chiral isoflavanes and α‐aryl hydrocoumarins.     

Synthese und Reaktionsverhalten 2′-substituierter Isoflavone

Synthesis and Behaviour of Isoflavones Substituted in 2′-Position The protected chalcones 6–8 prepared from acetophenone and benzaldehydes rearranged to the dimethoxypropanone derivatives 9–11 in the presence of trimethyl orthoformate by Tl(NO₃)₃. 3 H₂O. These compounds could be cyclized to the isoflavones 12–14 in high yields (Scheme 2). The conversion of these isoflavones to the corresponding isoflavanes (model compounds of the phytoalexin glabridin; see Scheme 1) was the main goal of this work. Hydrogenation of 13 and 14 gave the isoflavanes 15 and 16 , respectively and their deprotection the racemic natural product 4′-O-demethylvestitol ( 17 ). Reduction of 13 and 14 yielded different compounds depending on the reducing agent (Scheme 3). The saturated alcohols 20–23 could be obtained with NaBH₄ or LiBH₄. They were transferred into the racemic 9-O-demethylmedicarpin ( 24 ) and haginin D ( 25 ) under acidic conditions. The ketones 26–28 (Scheme 4) were obtained in high yields by reduction of 12–14 with DIBAH. Deprotection of 26 yielded the racemic 2,3-dihydrodaidzein ( 29 ). Compounds 13 and 27 as well as 20 and 22 showed different behaviour under reduction conditions with Li in liquid ammonia. An efficient method for the introduction of the MeOCH₂O and the MeOCH₂CH₂OCH₂ protecting groups into hydroxylated benzaldehydes and acetophenones (Scheme 5) is described. The appropriate experimental conditions depend on the regioselectivity and on the number of the protected groups. The protected aldehydes, especially those with a protected ortho OH group, show an extraordinary ionization behaviour in chemical-ionization mass spectrometry (isobutane; Scheme 6).     

Doping studies of the magnetic cobaltocuprate CoSr2Y2−xCexCu2O9±δ

A structural, magnetic and electronic study of the cobaltocuprate CoSr₂Y_2−xCe_xCu₂O_9±δ (x=0.5-0.8) has been performed. All materials crystallise in the orthorhombic Cmcm symmetry space group in which chains of corner linked CoO₄ tetrahedra run parallel to the 1 1 0 direction. An antiferromagnetic transition is observed for x=0.5-0.8; T_M increases with x. A change in the dimensionality of the magnetic order occurs at x=0.8 as the interchain distance increases to a critical value. There is charge transfer between the cuprate planes and cobaltate layer as Ce doping increases, so that Co³⁺ is partially oxidised to Co⁴⁺ with a concomitant reduction in the valence of Cu. Superconductivity is not observed in any of the samples and a crossover from Mott to Efros and Shklovskii variable range hopping behaviour is evidenced as x increases from 0.5 to 0.8.     

Strategies for determining the bioactive ingredients of honey‐processed Astragalus by serum pharmacochemistry integrated with multivariate statistical analysis

Honey‐processed Astragalus is a widely used traditional Chinese medicine that has a better effect on reinforcing “Qi” (vital energy) than the raw one. A comparative study of metabolites analysis between them in rat serum for finding the bioactive ingredients was carried out using serum pharmacochemistry and multivariate statistical analysis. The blood collection methods and time were optimized first. Then the prototypes and metabolites in serum samples after oral administration were investigated by ultra‐high‐performance liquid chromatography coupled with electrospray ionization quadrupole time‐of‐flight mass spectrometry integrated with principal component analysis and orthogonal partial least squares discriminant analysis. The contents of metabolites were also analyzed to evaluate the metabolic profile differences. As a result, nine prototypes and 36 metabolites were identified. Only two prototypes and 15 metabolites were different between raw and honey‐processed Astragalus. Their biotransformation reactions contained the process of oxidation, demethylation, and hydrolysis in phase I and glucuronide conjugation or sulfate conjugation in phase II. Most of the detected metabolites were transformed from isoflavones and isoflavanes. Our results expand the knowledge about the influence of honey‐processing on Astragalus and suggest the different curative effects between raw and honey‐processed Astragalus might due to their therapeutic material discrepancy.     

Tolerance factor rules for Sr1−x−yCaxBayMnO3 perovskites

Synthesis of new perovskite Sr_1−x−yCa_xBa_yMnO_3−δ compounds is described in detail and dependence of their phase stability and structural distortions on the tolerance factor is discussed. Oxygen contents have been measured over extended temperature and composition ranges. Neutron powder diffraction was used to precisely measure the A-O and Mn-O bond lengths and derive accurate interatomic distances [Ca-O], [Sr-O], [Ba-O], and [Mn-O]. By using these parameters instead of tabulated ionic radii we have derived the functional dependence of the tolerance factor t=t(x,y,T,δ) on composition, temperature, and oxygen content. At a fixed oxygen content, the tolerance factor is an increasing function of temperature as a result of greater thermal expansion of the average 〈A-O〉 bond relative to the 〈Mn-O〉 bond. We find that the stability of the perovskite phase at high temperature is governed, as expected, by the magnitude of tolerance factor (t?1) which can be adjusted by controlling the oxygen content 3−δ. This dependence of the tolerance factor on oxygen content and temperature can be utilized to design synthesis conditions for the controlled formation of the new, kinetically stable, perovskite phases.     

Crystal structure of Ln1/3NbO3 (Ln=Nd, Pr) and phase transition in Nd1/3NbO3

The crystal structure of the A-site deficient perovskite Ln_1/3NbO₃ (Ln=Nd, Pr) at room temperature has been determined, for the first time, as orthorhombic in space group Cmmm using high-resolution neutron powder diffraction. Pertinent features are the alternation of unoccupied layers of A-sites and layers partly occupied by Ln cations, as well as out-of-phase tilting of the NbO₆ octahedra around an axis perpendicular to the direction of the cation/vacancy ordering. The phase transition behaviour of Nd_1/3NbO₃ has also been studied in situ. This compound undergoes a continuous phase transition at around 650 °C to a tetragonal structure in space group P4/mmm due to the disappearance of the octahedral tilting. The analysis of spontaneous strains shows that this phase transition is tricritical in nature.     

Oxygen-ion and electron conductivity in Sr2(Fe1−xGax)2O5

High-temperature electrical conductivity measurements, structural data from powder X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy were combined to study the interrelationship of oxygen ion transport and p- and n-type transport in Sr₂(Fe_1−xGa_x)₂O₅, where x=0, 0.1 and 0.2. Although gallium substitution generally decreases the total ion-electron transport, the transition of the orthorhombic brownmillerite structure to a cubic phase on heating results in the recurrence of the conductivity to the same high level as in the parent ferrite (x=0). The changes of the partial contributions to the total conductivity as a function of x are shown to reflect a complicated interplay of the disordering processes that develop in the oxygen sublattice on heating in response to replacement of iron with gallium.     

Structure refinement, dielectric, pyroelectric and Raman characterizations of Ba1−xLax(1−y)/2Euxy/2Nax/2TiO3 solid solution

The perovskite-type oxides Ba_1−xLa_x(1−y)/2Eu_xy/2Na_x/2TiO₃ (0?x?0.5 and xy=0.04) were synthesized and characterized by X-ray diffraction as well as dielectric measurements and Raman spectroscopy. The crystal structure of these ceramics has been determined by the Rietveld refinement powder X-ray diffraction data at room temperature. These compounds crystallize at room temperature in tetragonal space group P4mm for 0?x?0.1 and in the cubic group for 0.2?x?0.5. The phase transition temperature T_C (or T_m) decreases as x content increases. The degree of diffuseness of the phase transition is more pronounced for higher x content, implying the existence of a composition-induced diffuse phase transition of the ceramics with x?0.1. The evolution of the Raman spectra was studied as a function of various compositions at room temperature. The polarization state was checked by pyroelectric measurements.     

N,N-Dimethyl-S-difluoromethyl-S-phenylsulfoximinium tetrafluoroborate: A versatile electrophilic difluoromethylating reagent

Over the past decade, sulfur-based fluoromethyl containing compounds have been exhaustively investigated as versatile fluoroalkylating reagents by our research laboratory as well as many others. Lately, we have designed a novel electrophilic difluoromethylating protocol employing in situ prepared N,N-dimethyl-S-difluoromethyl-S-phenylsulfoximinium salt. The present reagent provides excellent reactivity toward a broad spectrum of nucleophilic species (N-, P-, S-, and O-nucleophiles) to yield the corresponding difluoromethylated products with high efficacy under mild conditions. Additional studies have been performed to elucidate the mechanistic fundamentals of the reactions.     

The fragmentation reaction of 16R-bromopregnane-3S,20S-diol

16R-Bromopregnane-3S,20S-diol reacted with potassium t-butoxide to afford androst-16-en-3S-ol in a moderate yield via fragmentation reaction. The latter is a key intermediate for the synthesis of 5α-androst-16-en-3-one, as boar sex pheromone, and other steroidal drugs. In addition, 16R,20S-epoxypregnane-3S-ol was also obtained as a major product by changing the reaction solvent.     

Crystal structures and polymorphism in compounds Bi6+xT1−xP2O15+y, T=first row transition metals and Pb

The compounds Bi_6+xT_1−xP₂O_15+y, T=Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn and Pb display five polymorphic forms. Polymorph A is formed by the Ti, Mn, Fe and Ni phases. Polymorph B is exhibited by Co and Cu compounds. The Cr phase crystallizes as polymorphic form C and the Zn phase crystallizes as polymorph D. The Pb compound crystallizes in a new structure type designated as polymorph E. The transition metal crystal structures demonstrate a similar motive. OBi₄ tetrahedra share edges to form two-dimensional Bi₂O₂ layers that are spanned by PO₄ tetrahedra and TO_6−y octahedra, pyramids and a trigonal bipyramid to form a three-dimensional network. Polymorph A crystallizes in space group C2; polymorph B is centrosymmetric with space group C2/c, the unit cell parameters differ and the unit cell volume is about double. Polymorph C crystallizes in space group and polymorph D exhibits space group C2. Bi_6.4Pb_0.6P₂O_15.2 can be considered as polymorph E, space group C2, with a new crystal structure but related stoichiometry.     

Synthesis, crystal structure and magnetic properties of the spin ladder compounds La2(Cu1−xZnx)2O5 and La8(Cu1−xZnx)7O19

The influence of Zn-doping on the crystal structure and magnetic properties of the spin ladder compounds La₂Cu₂O₅ (4-leg) and La₈Cu₇O₁₉ (5-leg) have been investigated. The La₂(Cu_1−xZn_x)₂O₅ and La₈(Cu_1−xZn_x)₇O₁₉ solid solutions were obtained as single phases with x=0-0.1 via the solid-state reaction method in the temperature range between 1005-1010 °C and 1015-1030 °C in oxygen and air atmospheres, respectively. The lattice parameters a and c of the monoclinic crystal structures as well as the unit cell volume V increase with increasing x, while b and β decrease for both series. The magnetic susceptibilities χ of both series show a very similar behavior on temperature as well as on Zn-doping, which is supposed to be due to the similar Cu-O coordination in both La₂Cu₂O₅ and La₈Cu₇O₁₉. For low Zn-doping (x?0.04), a spin-chain like behavior is found. This quasi-one-dimensional behavior is strongly suppressed in both series for x?0.04. Here, the maximum (characteristic for spin chains) in χ(T) disappears and χ(T) decreases monotonically with increasing temperature.     

Thermodynamic determination of the cation distribution in NixMn1−γ−xFe2+γO4 ferrites

The cation distribution in the spinel ferrite system Ni_xMn_1−γ−xFe_2+γO₄ (x=0, 0.25, 0.5, 0.75 and γ=0.137) has been calculated analytically in complete form as a function of thermodynamic parameters. A generalized theoretical framework based on the O’Neill-Navrotsky model and Newton methods was used to solve a multicomponent system for up to 10 cation species. The relationship between the cation distribution and composition is given. The results are shown to agree with the available experimental results.     

Structural and magnetic characterization of Mn3IrGe and Mn3Ir(Si1−xGex): experiments and theory

The structural and magnetic properties of a new ternary Ir-Mn-Ge phase, Mn₃IrGe, as well as the solid solution Mn₃Ir(Si_1−xGe_x), 0?x?1, have been investigated by means of X-ray and neutron powder diffraction, magnetization measurements and first principles calculations. The crystal structure is cubic, of the AlAu₄-type (an ordered form of the β-Mn structure), Z=4, space group P2₁3, and the unit-cell dimension varies linearly with the silicon content. For all compositions, antiferromagnetic ordering is found below a critical temperature of about 225 K. The magnetic structure is noncollinear, as a result of frustrated magnetic interactions on a triangular network of Mn atoms, on which the moments rotate 120° around the triangle axes. The magnitude of the magnetic moment at 10 K is 3.39(4) μ_B for Mn₃IrGe. The theoretical calculations reproduce with very good accuracy the magnitudes as well as the directions of the experimentally observed magnetic moments.     

Magnetic properties of La0.5−xLnxSr0.5MnO3 (Ln=Pr, Nd, Gd and Y)

Magnetic and electron transport properties of four series of manganates of the composition La_0.5−xLn_xSr_0.5MnO₃ (Ln=Pr, Nd, Gd and Y) have been investigated to examine how the ferromagnetic metallic nature of the parent La compound changes over to antiferromagnetic insulating behavior, with change in Ln and x due to the associated changes in the A-site cation radius as well as the size disorder. When Ln=Pr and Nd, there is a transition from the tetragonal I4/mcm structure to the orthorhombic Immm and Imma structures at x=0.2 and 0.35, respectively. There is a gradual evolution of the properties from those of La_0.5Sr_0.5MnO₃ to those of Pr_0.5Sr_0.5MnO₃ or Nd_0.5Sr_0.5MnO₃ with increase in x. Thus, when x>0.2 and >0.35, respectively, the Pr- and Nd-substituted manganates show ferromagnetic transitions followed by antiferromagnetic transitions at low temperatures, with the ferromagnetic T_C decreasing with increasing x. The Gd and Y series of compounds are all orthorhombic and show a decrease in T_C with the increase in x, the ferromagnetism disappearing at high x. At a value of x corresponding to the A-site cation radius of Pr_0.5Sr_0.5MnO₃, the Gd and Y series of compounds exhibit ferromagnetism in the 250-300 K region and undergo an antiferromagnetic transition on cooling. The T_C−T_N gap is sensitive to the disorder arising from the size mismatch.     

Nickel deficiency in RENi2-xP2 (RE=La, Ce, Pr). Combined crystallographic and physical property studies

Large single crystals from RENi_2-xP₂ (RE=La, Ce, Pr) were synthesized from the pure elements using Sn as a metal flux, and their structures were established by X-ray crystallography. The title compounds were confirmed to crystallize in the body-centered tetragonal ThCr₂Si₂ structure type (space group I4/mmm (No. 139); Pearson's symbol tI10), but with a significant homogeneity range with respect to the transition metal. Systematic synthetic work, coupled with accurate structure refinements indicated strong correlation between the degree of Ni-deficiency and the reaction conditions. According to the temperature dependent dc magnetization measurements, LaNi_2-xP₂ (x=0.30(1)), as expected, is Pauli-like paramagnetic in the studied temperature regime, while the Ce-analog CeNi_2-xP₂ (x=0.28(1)) shows the characteristics of a mixed valent Ce³⁺/Ce⁴⁺ system with a possible Kondo temperature scale on the order of 1000 K. For three different PrNi_2-xP₂ (x?0.5) samples, the temperature and field dependence of the magnetization indicated typical local moment 4f-magnetism and a stable Pr³⁺ ground state, with subtle variations of T_C as a function of the concentration of Ni defects. Field-dependent heat capacity data for CeNi_2-xP₂ (x=0.28(1)) and PrNi_2-xP₂ (x=0.53(1)) are discussed as well.     

Synthesis and properties of the Co7Se8−xSx and Ni7Se8−xSx solid solutions

We report the synthesis and elementary properties of the Co₇Se_8−xS_x (x=0-8) and Ni₇Se_8−xS_x (x=0-7) solid solutions. Both systems form a NiAs-type structure with metal vacancies. In general, the lattice parameters decrease with increasing x, but in the Ni₇Se_8−xS_x system c increases on going from x=5 to 7. Magnetic susceptibility measurements show that all samples exhibit temperature-independent paramagnetism from 25-250 K. Samples within the Co₇Se_8−xS_x system, as well as Ni₇Se₈ and Ni₇SeS₇, were found to be poor metals with resistivities of ∼0.20 and ∼0.06 mΩ cm at 300 K, respectively. The Sommerfeld constant (γ) was determined from specific heat measurements to be ∼13 mJ/mol_CoK² and ∼7 mJ/mol_NiK² for Co₇Se_8−xS_x and Ni₇Se_8−xS_x, respectively.     

Structural characterization and physical properties of the system La1.33LixCrxTi2−xO6

New phases which arise from partial substitution of Ti⁴⁺ by Cr³⁺ and Li⁺ of the compound La_2/3TiO₃ have been obtained, giving rise to the series La_1.33Li_xCr_xTi_2−xO₆ (x=0.66, 0.55 and 0.44). These phases adopt a perovskite-type structure as deduced from their structural characterization. Rietveld's analyses of neutron diffraction data show that it is orthorhombic (S.G. Pbnm) with ordered domains. Conductivity has been examined by complex impedance spectroscopy and it increases with increasing lithium and chromium content. These materials behave as mixed conductors with low activation energies. Magnetic susceptibility variation with temperature shows antiferromagnetic interactions at the lowest temperatures.     

Ruthenium-catalyzed reduction of N-alkoxy- and N-hydroxyamides

A ruthenium-catalyzed reduction of N-alkoxy- and N-hydroxyamides was found to afford corresponding amides in good to high yields. A simple RuCl₃/Zn-Cu/alcohol system, without the addition of any other ligands, exhibited a high catalytic activity, and therefore the present reaction does not require a stoichiometric amount of metals or metal complexes as reductants. When β-substituted-α,β-unsaturated N-methoxyamides were employed as substrates, concurrent hydrogenation of the olefin moiety proceeded slowly with deprotection of the methoxy group. In the reduction of N-hydroxyamides, the alcoholic solvent was found to function as a hydrogen donor.     

Structural Characterization of YMexMn1−xO3 (Me=Cu, Ni, Co) Perovskites

The structural properties of the YMe_xMn_1−xO₃ (Me=Cu, Ni, Co) pseudobinary oxides have been studied by X-ray diffraction and electrical measurements. The powders were prepared by solid state reaction between the corresponding oxides. The incorporation in solid solution of small divalent cations, Cu²⁺, Ni²⁺, and Co²⁺, substituting for Mn in the hexagonal YMnO₃ compound, leads to a phase transition in which a perovskite-type structure is formed. The amount of substituting cation necessary for such a transition depends on the cation nature and, to a small extent, on the ionic radius. The phase transition depends strongly on the progressive substitution of the Jahn-Teller Mn³⁺ cation and therefore of the cooperative Jahn-Teller interaction weakness. The steric influence plays a secondary role, as is shown by the very small variation of the tolerance factor, t, as a function of the cation content. The solid solutions with perovskite-type structure show semiconducting behavior. The conductivity mechanism is of a thermally activated small polaron hopping.