Asymmetric synthesis of abietane diterpenoids via B-alkyl Suzuki-Miyaura coupling. Formal total asymmetric synthesis of 12-deoxyroyleanone and cryptoquinone

A convergent synthetic strategy for abietane diterpenoids via B-alkyl Suzuki-Miyaura coupling and Lewis acid-mediated cyclization reactions is established. Asymmetric total synthesis of 12-deoxyroyleanone, an antileishmanial diterpene, is described.     

Enantioselective spiro ene-carbocyclization of 1,6-enynes catalyzed by tropos rhodium(I) complex with skewphos ligand

A tropos rhodium(I) complex having skewphos ligand is shown to be a highly enantioselective catalyst for asymmetric ene-type carbocyclization of 1,6-enynes with tri-substituted olefins to control quaternary stereogenic centers or spiro-rings.     

Singular integral operators on 53-0153-0153-01-spaces

Summary It is shown that certain singular integral operators with variable kernels leave invariant theL ^v, -spaces studied by Campanato, Stampacchia, Peetre and others. Our results extend Peetre's work on convolution operators.     

Preparation and Mössbauer effect of Cr1−xFexOOH (0 ≦ x ≦ 1.0) with the InOOH-type structure

The complete solid solutions of Cr_1?xFe_xOOH with the InOOH-type structure were synthesized under high pressures. They were antiferromagnetic with Néel temperatures of 570 K for FeOOH, 454 K for Cr_0.2Fe_0.8OOH, 332 K for Cr_0.4Fe_0.6OOH, and 160 K for Cr_0.6Fe_0.4OOH as determined by the Mössbauer effect measurements.     

A highly diastereoselective pinacol coupling reaction of aldehydes and ketones using low-valence niobium generated from Nb(V)

A simple method for the diastereoselective synthesis of racemic 1,2-diol mediated by low-valence niobium generated in situ is described. A 1,4-dioxane-toluene solvent system was found to be essential to achieve higher selectivities and to prevent other reactions of pinacols, such as deoxygenation and acetal formation. Aromatic aldehydes and ketones were converted to the corresponding pinacols with up to 97 and 85% de, respectively.     

Synthesis of calix[4]arene library substituted with peptides at the upper rim

A fluorescence-labeled calix[4]arene library substituted with peptides at the upper rim was synthesized. Screening of the library for binding a dye-labeled oligopeptide indicated that some peptidocalix[4]arenes selectively bind the oligopeptide. The chemosensitivity of the library members for a target peptide was also investigated.     

Direct capillary gas chromatographic analysis and thermal stability of bile acid esters of glucose

Summary This paper deals for the first time with a direct method for analysis of the α and β anomers of bile acid esters of glucose by capillary gas chromatography (CGC) without the need for a hydrolytic step. The bile acid esters were derivatized to their trimethylsilyl (TMS) ethers, which in turn were chromatographed on a short (7m) metal capillary column chemically coated with a thin (0.15 μm) film of thermostable, non-polar polydimethylsiloxane. Satisfactory CGC separation of the isomeric bile acid esters was achieved on the column; the β anomers eluted before the corresponding α isomers. Particularly noteworthy is that the α anomers are partially isomerized to the corresponding β anomers, and that both anomers are partially decomposed during CGC analysis, demonstrating the chemical specificity and thermal instability of the bile acid esters.     

Palladium-Catalyzed Decarboxylative Alkynylation of α-Acyloxyketones by C(sp3)−O Bond Cleavage

Palladium-catalyzed decarboxylative alkynylation of α-acyloxyketones triggered by C(sp³)−O bond cleavage is disclosed. The decarboxylation strategy featuring a neutral reaction condition enabled an unprecedent catalytic alkynylation of a ketone enolate. The reaction was applied to a variety of substrates, giving desired products in good yields. We successfully obtained X-ray crystallography of a new palladium–enolate intermediate that was synthesized by a reaction of [Pd(cod)(CH₂TMS)₂] with XPhos and α-acyloxyketone at room temperature, indicating facile C(sp³)−O bond disconnection.     

Studies on the syntheses of polymetalloxanes and their properties as a precursor for amorphous oxide. IV. Properties of SiO2–TiO2 oxide fibers from polytitanosiloxane

From polytitanosiloxanes (PTS), SiO₂–TiO₂ oxide fibers with fairly good tensile strength were prepared, and their mechanical and thermal properties were investigated. The precursor fibers PTS-0.5 and PTS-1.0 were obtained by dry spinning of a highly viscous PTS solution which were formed as the reaction mixture of silicic acid (SA) with bis(2,4-pentanedionato)titanium diisopropoxide (PTP) in the molar ratios (SA/PTP) of 0.5 and 1.0. The precursor fibers PTS-0.5 were too brittle to measure their tensile strength, whereas PTS-1.0 and the heat-treated fibers were found to have tensile strength of 130 (precursor), 540 (500°C), and 450 (900°C) MPa, respectively. Heat-treatment of the fibers PTS-1.0 at above 1000°C forms anatase and rutile of titanium dioxide. The crystallization is resulted from the unreacted PTP which is not incorporated into the polymer network.