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Mg-loaded todorokite-type Mg0.2MnO2·0.5H2O nanowires are obtained by hydrothermal treatment of a dispersion of buserite-type manganese oxide in 1 M MgCl2 solution (autoclave, 180—220 °C, 1—4 d).

Zerovalent metal atoms (such as Cu, Ag, Sn, Au, In, Co, Fe, Ni) are intercalated into two-dimensional layered Bi2Se3 nanoribbons using disproportionation redox reactions or carbonyl decomposition to generate dilute zerovalent metal atoms in a refluxing solution.

K4Sn9 dissolves in en to give equilibrium mixtures of the diamagnetic HSn93- ion along with KxSn9(4-x)- ion pairs (x = 0, 1, 2, 3).

Up to 60 at.% copper can be intercalated into layered Bi2Se3 nanoribbons without disrupting the host lattice.

The intramolecular [2+2] photocycloaddition of 2-acyloxy-2-3-hexenoylcyclohexenones has been shown to be highly diastereoselective. The cycloadditions produce exclusively cis fused products and the sense and level of selectivity is consistent with a molecular mechanics model for initial bond formation in the stepwise cycloaddition.

Three new titanium oxysulfides, La8.75Ti9.25S24O4, La8.50Ti9.50S24O4, and La8.10Ti8.05S24O4, were prepared by high-temperature methods (1025−1050 °C; ∼80−150 h) from La2S3, Ti, S, and either La2O3 or TiO2 as oxygen sources. LaCl3 (∼10−30 wt %) was added as a flux. The compounds were characterized by single-crystal X-ray diffraction, neutron activation analysis, and EDX analysis. All three compounds contain common [(Ti4S2O4)(TiS6)4/2](12+δ)- oxysulfide layers and disordered/variable composition titanium sulfide layers that alternately stack along the c-axis of the unit cell. The titanium sulfide layers contain extensive La/Ti solid solution formation and are characterized by 5-fold disorders at the M(2) octahedral sites and 2-fold disorders at the M(3) sites. These compounds are members of a series of compounds with the general formula La8+xTi8+yS24O4, where (x + y) ≤ 2 and the oxidation states of Ti can vary from +3 to +4. Crystal data (153 K) of La8.75Ti9.25S24O4: tetragonal space group P4/mmm, a = 10.4...

A number of highly cytotoxic polyketides, including the anguinomycins,1 leptofuranins,2 leptomycin,3 and kazusamycin,4 having similar gross chemical structures have been isolated from Streptomyces strains. Recently, a structurally related polyketide, callystatin A 1, was isolated from the marine sponge, Callyspongia truncata, in the Nagasaki Prefecture.5 Callystatin A shows remarkable in vitro cytotoxicity (IC50 ) 0.01 ng/mL) against KB cells. The relative and absolute stereostructure of callystatin A was established by a combination of spectroscopic methods and chemical synthesis.5-7 The limited quantities of callystatin A available from natural sources, as well as the possibility for carrying out syntheses and structure elucidation of the related antitumor antibiotics, prompted us to pursue a total synthesis of callystatin A.8 Here we disclose the asymmetric total synthesis of (-)-callystatin A exploiting our recently developed asymmetric aldol protocol with chlorotitanium enolates of acyl oxazolidinethiones.9 Strategically, E-selective olefination10 of aldehyde 2 (Scheme 1) with the phosphorane derived from tributylphosphonium salt 3 appeared to offer the most convergent assembly of callystatin A. Aldehyde 2 representing C1 to C12 would be constructed from a similar olefination between the masked pyranone aldehyde 4 (Scheme 2) and phosphonium salt 5 (Scheme 3). The C13 to C22 propionate fragment 3 was to be constructed through consecutive asymmetric aldol additions9 employing acyl oxazolidinethione 6 (Scheme 4). The synthesis of aldehyde 4 began with S-glycidol 7 as illustrated in Scheme 2. Protection of S-glycidol as its TBDPS ether followed by copper-catalyzed epoxide opening with vinylmagnesium bromide provided the alcohol 8 in 85% overall yield. Conversion of the secondary alcohol to the isopropoxy propenyl ether provided a mixed acetal which was exposed to the Grubbs catalyst11 to effect ring-closing metathesis to dihydropyran 9 (71% overall). Removal of the TBPDS protecting group with n-Bu4

The synthesis of the C1−C13 fragment 3 of leucascandrolide A has been completed utilizing a stereoselective and regioselective reductive cleavage of a highly functionalized spiroketal to incorporate the cis-2,6-disubstituted tetrahydropyan. The spiroketal was constructed by addition of a lithiated pyrone 5 to aldehyde 6.

The compound Sr6V9S22O2 was prepared from SrS, sulfur, vanadium metal, and V2O5 at 950 degrees C in an evacuated quartz tube. The compound is rhombohedral, R3, with a = 8.7538(6) A, c = 34.934(3) A, and Z = 3, and shows strong preferred orientation in its XRD profiles (00l) due to the layered nature of the structure. The compound contains charged CdI2 type VS2 layers of formula [V7S14]4- separated by [Sr6(VOS3)2(S2)]4+ layers. The latter has VOS3(3-) tetrahedra and S2(2-) disulfide units linked by Sr2+ ions. Magnetic susceptibility and four-probe resistivity studies show essentially temperature-independent paramagnetism above 80 K and small gap semiconductor behavior, respectively. The compound has a positive Hall coefficient at room temperature. The relationship among Sr6V9S22O2, "SrV2S5" (J. Solid State Chem. 1996, 126, 189), and other AM2S5 phases is discussed.

Asymmetric aldol additions using chlorotitanium enolates of N-acyloxazolidinone, oxazolidinethione, and thiazolidinethione propionates proceed with high diastereoselectivity for the Evans or non-Evans syn product depending on the nature and amount of the base used. With 1 equiv of titanium tetrachloride and 2 equiv of (−)-sparteine as the base or 1 equiv of (−)-sparteine and 1 equiv of N-methyl-2-pyrrolidinone, selectivities of 97:3 to >99:1 were obtained for the Evans syn aldol products using N-propionyl oxazolidinones, oxazolidinethiones, and thiazolidinethiones. The non-Evans syn aldol adducts are available with the oxazolidinethione and thiazolidinethiones by altering the Lewis acid/amine base ratios. The change in facial selectivity in the aldol additions is proposed to be a result of switching of mechanistic pathways between chelated and nonchelated transition states. The auxiliaries can be reductively removed or cleaved by nucleophilic acyl substitution. Iterative aldol sequences with high diastere...

The chemoselective functionalization of 5-bromo-2-chloro-3-fluoropyridine (1c) is described. Catalytic amination conditions (Pd2dba3, Xantphos, base) afford exclusively the bromide substitution pro...

K3Sb7 and Ni(COD)2 react in the presence of 2,2,2-cryptand in ethylenediamine solutions (∼1:8 Ni/Sb molar ratio) to give dark-brown crystals of the paramagnetic cluster anion [Ni5Sb17]4- as the [K(2,2,2-crypt)]+ salt. The cluster has a Ni(cyclo-Ni4Sb4) ring unit that sits inside a Sb13 bowl. The structure is similar to that of the previously reported [Pd7As16]4- ion containing a Pd(cyclo-Pd4As4) ring unit that sits inside a Pd2As12 bowl. Density functional theory and bond valence analyses suggest delocalized charge distributions and intermetallic-like properties.

The ligand-free [Ni2Sn17]4- ion comprises two [Ni@Sn9]2- clusters that share a common vertex. The cluster sequentially loses Sn atoms in the gas phase and shows global exchange of all Sn atoms on the NMR time scale in solution at 60 °C. At lower temperatures, the fluxionality is localized to the ends of the cluster and does not involve the central 8-coordinate Sn5 atom.

β-ZrNCl reacts with excess NaF in the solid state (350−400 °C) via anion exchange to give metastable NaxZrNF1+x (x ≈ 0.3), the first fluoride structural analogue of the MNX system (M = Zr, Hf; X = Cl, Br, I). The sodium-stabilized phase (P63/mmc; a = 3.654(1) A, c = 18.266(8) A) was characterized by powder X-ray and neutron diffraction studies and was shown to contain successive FZr2N2F layers that are shifted from the original ZrNCl parent structure, giving a two-layer unit cell. Partially occupied Na and F sites create a stabilizing cluster effect between these layers. Heating the reaction mixture above 500 °C leads to the formation of the ZrNxF4-3x phase reported by Jung and Juza. Further heating results in decomposition to several known sodium fluorozirconate phases.

We describe the synthesis and investigations of Pb2MnReO6 in perovskite and pyrochlore modifications. Both the modifications are formed at atmospheric pressure, the perovskite (I) at 550 °C and the pyrochlore (II) at 600 °C. Rietveld refinements of the structures using the powder XRD data show that oxide I adopts the monoclinic (P21/n) double perovskite structure with partial ordering (∼72%) of MnII/ReVI at the octahedral sites, while oxide II crystallizes in a defect-pyrochlore structure where MnII/ReVI are disordered at the octahedral sites. The frustrated cation sublattice precludes a long-range ordering of Mn/Re in the pyrochlore structure. I is a semiconductor showing evidence for a ferrimagnetic ordering at Tc ∼ 100 K, but the small saturation magnetic moment (〈S〉 = 0.81) and the divergence between FC and ZFC magnetization data are consistent with spin-glass-like behavior and a partially ordered Mn/Re in the double perovskite structure. On the other hand, both the Curie−Weiss paramagnetism down to ∼...

A general and efficient synthesis of carbocyclic and hexenopyranosyl nucleosides has been developed. The strategy combines three key transformations: an asymmetric aldol addition to establish the relative and absolute configuration of the pseudosugar, a ring-closing metathesis to construct the pseudosugar ring, and a Trost-type palladium(0)-mediated substitution to assemble the pseudosugar and the aromatic base. Carbovir, abacavir, and their 2'-methyl derivatives as well as hexenopyranosyl nucleoside analogues have been prepared by this sequence.