Oxidative radical cyclization on enamide systems using n-Bu3SnH and dilauroyl peroxide

Efficient 5-endo and 6-endo oxidative radical cyclizations on enamide systems are described using nBu₃SnH and dilauroyl peroxide both as initiator and oxidant. Dibenzoyl peroxide and dicumyl peroxide were also tested in the same reaction and the product yields were very similar to those obtained with dilauroyl peroxide. The erythrina ring system was constructed in a two-step sequence featuring this novel process.     

Synthesis and characterization of n=5, 6 members of the La4Srn−4TinO3n+2 series with layered structure based upon perovskite

Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La₄Sr_n−4Ti_nO_3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)₅Ti₅O₁₇] and [(La,Sr)₆Ti₆O₂₀] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]_p. The n=5 member is similar to the previously reported n=5 member of other A_nB_nO_3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this A_nB_nO_3n+2 series.     

Z/E Stereoselective synthesis of β-bromo Baylis-Hillman ketones using MgBr2 as promoter via a one-pot three-component reaction

The first time steroselective synthesis of (Z)-β-bromo Baylis-Hillman ketones has been achieved using a one-pot three-component reaction. The new system uses MgBr₂ as both the Lewis acidic promoter and the bromine source for the Michael-type addition with α,β-acetylenic ketones to form an active β-bromo allenolate intermediate, which in turn attacks various aldehydes to afford β-bromo Baylis-Hillman adducts in good yields and Z-selectivity.     

Mild and practical stereoselective synthesis of (Z)- and (E)-allyl bromides from Baylis-Hillman adducts using Appel agents (PPh3/CBr4): a facile synthesis of semiplenamides C and E

Appel agents (PPh₃/CBr₄) have been utilized for high-yielding stereoselective synthesis of (Z)- and (E)-allyl bromides from Baylis-Hillman adducts at room temperature. The method has been applied for the synthesis of naturally occurring bioactive fatty acid amides, semiplenamides C and E.     

Excess enthalpies of alkane-1-amines {CnH2n+1NH2, n = 3-8} + methyl methylthiomethyl sulfoxide and +dimethyl sulfoxide at 298.15 K

Excess enthalpies of binary mixtures between each of alkane-1-amines {C_nH_2n+1NH₂, n=3-8} and methyl methylthiomethyl sulfoxide (MMTSO) or dimethyl sulfoxide (DMSO) have been determined at 298.15 K. All mixtures showed positive enthalpy changes over the whole range of mole fractions.The limiting excess partial molar enthalpies of the aliphatic amines, H₁^E,∞, of all the mixtures with MMTSO or DMSO studied were smaller than those of MMTSO or DMSO, H₂^E,∞, respectively. Linear relations are obtained between limiting excess partial molar enthalpies and number of methylene groups.     

Differential 3ω calorimeter

We have developed a new dynamic calorimeter using the differential 3ω detection method. The differential 3ω calorimeter is capable of measuring dynamic heat capacity of liquid samples. The new calorimeter consists of a Wheatstone bridge made of two identical heater/sensors, and is based on the sensitive null detection method. The balancing is done automatically at all frequencies and is independent of temperature; once a sample is placed on one heater/sensor, a third harmonic signal is produced due to the difference in the two arms of the bridge. The differential 3ω calorimeter provides enhancements over traditional dynamic methods in dynamic range (up to 30 kHz), resolution, and ease of operation.     

Structure and magnetic properties of the orthorhombic n=2 Ruddlesden-Popper phases Sr3Co2O5+δ (δ=0.91, 0.64 and 0.38)

The reduced Ruddlesden-Popper phases, Sr₃Co₂O_5+δ with δ=0.91, 0.64 and 0.38, have been prepared in a nitrogen atmosphere. The crystal structures were determined by powder neutron diffraction. Oxygen vacancies are found both in O(3) and O(4) sites but the majority are along one crystallographic axis in the CoO₂ plane, inducing an orthorhombic distortion of the normally tetragonal n=2 Ruddelsden-Popper structure. Superstructures due to oxygen ordering are observed by electron microscopy. The magnetic measurements reveal complex behavior with some ferromagnetic interactions present for Sr₃Co₂O_5.91 and Sr₃Co₂O_5.64.     

Stereoselective synthesis of (E)- and (Z)-3-hydroxy-2-methyl-1-alkenyl iodides by base-promoted ring-opening of iodomethylated epoxides

Both (E)- and (Z)-3-hydroxy-2-methyl-1-alkenyl iodides were stereoselectively synthesized from iodomethylated epoxides by treatment with sodium hexamethyldisilazane in DMF and with LDA in THF (or lithium 2,2,6,6-tetramethylpiperidide in THF), respectively.     

A highly efficient stereoselective synthesis of (Z)- and (E)-allyl iodides from Baylis-Hillman adducts

A highly efficient synthesis of (Z)- and (E)-allyl iodides has been accomplished by treatment of Baylis-Hillman adducts with iodine and triphenylphosphine in methylene chloride at room temperature. The method is associated with mild reaction conditions, high yields and excellent stereoselectivity.     

Intercalation behavior of n-alkylamines into an A-site defective layered perovskite H2W2O7

Intercalation behavior of n-alkylamines into a protonated form of an A-site defective layered perovskite H₂W₂O₇ has been investigated. Results from XRD indicate these materials are layered with the corresponding interlayer spacing governed by the n-alkylamine chain length, and a reversible intercalation and deintercalation property is observed among these intercalation compounds. The IR spectra of the intercalation compounds with n-alkylamines clearly show that n-alkyl chains possess an all-trans conformation, and H₂W₂O₇ accommodate n-alkylamines (C_nH_2n+1NH₂: n=3, 4, 7, 8, 12, 16) to form intercalation compounds via an acid-base mechanism. A linear relationship between the interlayer distance and the number of carbon atoms in n-alkyl chains is observed to show a bilayer arrangement of the n-alkyl chains with a tilt angle of ∼71.6°. Elemental analysis studies reveal that the amounts of intercalated n-alkylamines are about 2.0 mol per [W₂O₇]. Despite the surface geometry of H₂W₂O₇ is almost identical to those of layered perovskites H₂[A_n−1B_nO_3n+1], the amounts of intercalated n-alkylamines of them are different. A reasonable explanation is given through our research.     

Controlled morphology synthesis of β-FeOOH and the phase transition to Fe2O3

The hexagram and arrayed β-FeOOH nanorods were first synthesized free of surfactants through the solvent-thermal method. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrum (EDAX) and thermal gravimetric analysis (TGA) were used to characterize the as-prepared products. The TEM and FESEM images showed that hexagram β-FeOOH and arrayed rod-like β-FeOOH with an average diameter of 10-15 nm and an average length of 100 nm (aspect ratio is about 10) were prepared. Electrochemical tests show that these nanorods deliver a large discharge capacity of 277 mA h g⁻¹ versus Li metal at 0.1 mA cm⁻² (voltage at 1.5-4.2 V). Treated the as-synthesized rod-like β-FeOOH by annealing, rhombus hematite was obtained.     

Prediction of molecular weight and density of n-alkanes (C6-C44)

Heavy n-alkanes and their mixtures were characterized by high temperature-simulated distillation using gas chromatography with a capillary column. In this work, the atmospheric boiling point is determined by the HT-SimDis GC method. In this study, molecular weights and density of n-alkanes were evaluated with this method by using retention times and normal boiling points as input data. ASTM D2887 calibration mixture containing 17 n-alkanes in the C₆-C₄₄ range were used for qualitative analyses. Retention times (t_R) of n-alkanes were measured with this method. The other input data that normal boiling points (T_b) and molecular weight (M) had been taken in the literature. Experimental densities (at 20 °C) of n-alkanes were obtained from API Research Projects. Empirical molecular weight and density correlations were developed by using the nonlinear and multiple regressions with correlation coefficients. The results of calculations were compared with experimental data. Normal boiling point predictions were obtained as an average absolute deviation of 1.07%. Molecular weight and density results were evaluated as average absolute deviations of 0.68% and 0.21%, respectively.     

Direct syntheses of Lan+1NinO3n+1 phases (n=1, 2, 3 and ∞) from nanosized co-crystallites

A new direct route for the “bottom up” syntheses of phases in the La_n+1Ni_nO_3n+1 series (n=1, 2, 3 and ∞) has been achieved via single-step heat treatments of nanosized co-crystallized precursors. The co-crystallized precursors were prepared using a continuous hydrothermal flow synthesis system that uses a superheated water flow at ca. 400 °C and 24.1 MPa to produce nanoparticulate slurries. Overall, a significant reduction in time and number of steps for the syntheses of La₃Ni₂O₇ and La₄Ni₃O₁₀ was achieved compared with more conventional synthesis methods, which typically require multiple homogenization and reheating steps over several days.     

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.     

Stereoselective synthesis of (−)-tetrahydrolipstatin via a radical cyclization based strategy

An efficient and flexible approach for the total synthesis of (−)-tetrahydrolipstatin is described. The main features of the synthetic strategy are a stereocontrolled radical cyclization and the successful utilization of commercially available S-malic acid.     

Transmission electron microscopy study of Ruddlesden-Popper Can+1MnnO3n+1n=2 and 3 compounds

Two Ruddlesden-Popper compounds Ca_n+1Mn_nO_3n+1 with n=2 and 3 synthesized by a citrate gel technique have been studied by TEM. The structure of Ca₄Mn₃O₁₀ is consistent with the previously determined structure having the space group Pbca and a⁻ a⁻ c⁺/a⁻ a⁻ c⁺ tilt system. The presence of defects suggests the possible high-temperature phase transition from untilted I4/mmm to Pbca. The structure of Ca₃Mn₂O₇ was found to be different from the previously suggested I4/mmm symmetry. Ca₃Mn₂O₇ forms with an orthorhombic structure with either Cmcm or Cmc2₁ space group. A structural model for Cmc2₁ based on the tilting of almost-rigid octahedra with a⁺ c⁻ c⁻/a⁺ c⁻ c⁻ tilt system is proposed. The lamellar defects were shown to be twin variants of the Cmc2₁ structure with the (001)_t interfaces, which suggests the possible tilting phase transition from the ideal I4/mmm to Cmc2₁ following the maximal group-subgroup symmetry tree: I4/mmm→Fmmm→Bbmm(Cmcm)→Bb2₁m(Cmc2₁).     

Synthesis and structure of a 1,6-hexyldiamine heptaborate, [H3N(CH2)6NH3][B7O10(OH)3]

A new 1,6-hexyldiamine heptaborate, [H₃N(CH₂)₆NH₃][B₇O₁₀(OH)₃] (1), has been solvothermally synthesized and characterized by single-crystal X-ray diffraction, FTIR, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in monoclinic system, space group P2₁/n with a=8.042(2) Å, b=20.004(4) Å, c=10.103(2) Å, and β=90.42(3)°. The anionic [B₇O₁₀(OH)₃]_n²ⁿ⁻ layers are interlinked via hydrogen bonding to form a 3D supramolecular network containing large channels, in which the templated [H₃N(CH₂)₆NH₃]²⁺ cations are located.     

Stereoselective iodine-induced cyclisation of alkene acetals. Application to the synthesis of 3-deoxy-exo-glycals and substituted tetrahydrofurans

2,5-Substituted tetrahydrofurans have been stereoselectively prepared by a iodine-induced cyclisation of alkene acetals, and the iodo derivatives obtained were transformed into 3-deoxy-exo-glycals and in polyhydroxy substituted tetrahydrofurans.     

Uragogin and blepharodin, unprecedented hetero-Diels-Alder adducts from Celastraceae species

Uragogin and blepharodin were isolated from Crossopetalum uragoga and Maytenus magellanica, respectively. They represent the first examples of a triterpene-neolignan ester and a heptacyclic arylpropanoid-nor-triterpenephenol, hetero-Diels-Alder adducts built with dioxane bridges. Their proposed biosynthetic route is discussed.