Enantioface-selective palladium-catalyzed silaboration of allenes via double asymmetric induction

Enantioenriched beta-borylallylsilanes were synthesized by palladium-catalyzed enantioface-selective addition of the silicon-boron bond to terminal allenes using a palladium catalyst possessing a chiral monodentate phosphine ligand. Use of a silylborane bearing a chiral auxiliary on the boron atom was beneficial to gain enantioface selectivities as high as 96% de.     

Construction of the benzylic quaternary carbon center of zoanthenol by intramolecular Mizoroki-Heck reaction of enone

[reaction: see text]. Stereocontrolled synthesis of the ABC ring framework of zoanthenol has been achieved. Our studies show that a beta,beta-disubstituted enone can act as a good acceptor of arylpalladium intermediates in the formation of a congested benzylic quaternary carbon center through an intramoleculer Mizoroki-Heck reaction. The cis B/C ring system was stereoselectively converted to the trans-fused framework through a SmI2-promoted deoxygenation of the alpha-hydroxy ketone.     

Photocrosslinking of poly(2,3-epithiopropyl methacrylate) by the oxidation of pendant episulfide groups

In the photocrosslinking of poly(2,3-epithiopropyl methacrylate) (PETMA) films the effect of the pendant episulfide group's oxidation on the crosslinking of PETMA was investigated. Thermal crosslinking of PETMA is promoted by peroxides such as benzoyl peroxide and hydrogen peroxide. IR spectrum of the crosslinked PETMA showed that the reaction proceeded through the oxidation of episulfide groups by the peroxides. The anthracene (An) sensitized photocrosslinking of PETMA films also proceeded via the oxidation of episulfide groups by singlet oxygen. It was found that residual tetrahydrofuran (THF) in the films remarkably increased the rate of the photocrosslinking and/or reduced the induction period. From the further investigation concerning casting solvents it was found that residual CS₂, CCl₄, and CHCl₃ in films increased the rate of the photocrosslinking and/or reduced the induction period of the photocrosslinking. The disappearance rate of An in the films was also increased by the presence of residual CS₂, CCl₄, and CHCl₃, differring from the result of THF. These results were explained by a difference in lifetime of singlet oxygen in the films. From the results were explained by a difference in lifetime of singlet oxygen in the films. From the results concerning the effects of hydroperoxides such as THF hydroperoxide and t-butyl hydroperoxide on the photocrosslinking of PETMA films the acceleration effect of the residual THF was deduced to be due to the promotion of singlet oxygen-oxidation of sulfide groups by protic compounds such as THF hydroperoxide and H₂O in the THF.     

Magnetic/Conducting Hybrid Compound Composed of 1-D Chain [Mn2Cl5(EtOH)]∞ and BEDT-TTF Stacking Layer

An assembled compound (BEDT-TTF)₂[Mn₂Cl₅(EtOH)] (1) consisting of two structural lattices of Mn(II)-Cl one-dimensional (1-D) chains and bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) stacking layers was synthesized by electrochemical crystallization. Compound 1 crystallized in triclinic space group P-1 (#2) with a=13.1628(5) Å, b=20.3985(9) Å, c=7.4966(3) Å, α=98.3498(8)°, β=104.980(1)°, γ=74.602(2)°, V=1868.3(1) ų, and Z=2. The 1-D chains and the stacking layers are aligned along the c-axis of the unit cell. The 1-D chain is described as [Mn₂Cl₅(EtOH)]_∞⁻ in which two Mn(II) ions and four Cl⁻ ions form a ladder-like chain with Kagomé (cuboidal) sublattices, and the remaining Cl⁻ ion and an ethanol molecule cap the edge-positioned Mn(II) ions of the chains. The BEDT-TTF molecules are packed between the Mn-Cl chains (ac-plane), the intermolecular S·S contacts of which are approximately found in the range 3.440(2)-3.599(2) Å. The packing feature of BEDT-TTF molecules is very similar to that of (BEDT-TTF)₂ClO₄(TCE)_0.5 (TCE=1,1,2-trichloroethane) (J. Am. Chem. Soc., 105, 297 (1983)). Regarding the electronic state of each BEDT-TTF molecule, Raman spectroscopic analysis and ESR study revealed the presence of half-valence BEDT-TTF molecules (charge delocalization) in 1. Magnetic measurements clearly demonstrated that the paramagnetic spins on the 1-D chain [Mn₂Cl₅(EtOH)]_∞⁻ arrange antiferromagnetically in the low-temperature region. Additionally, 1 exhibits metallic conductivity in the temperature range 2.0-300 K (σ=21 S cm⁻¹ at 300 K and 1719 S cm⁻¹ at 2.0 K), due to the contribution of the stacked BEDT-TTFs. Consequently, these peculiarities that correspond to antiferromagnetic/metallic conductivity demonstrate the “bi-functionality” of 1.     

Novel assembly of cyclic ethers by coupling alpha-chlorosulfides and alcohols

A novel protocol for assembling polycyclic ethers was developed and successfully applied to the synthesis of the EFGH ring system of ciguatoxin CTX3C. A key transformation involves construction of an O,S-acetal through coupling of alpha-chlorosulfide and a secondary alcohol under mild conditions. The method is highly applicable to use with sensitive substrates and will enable the synthesis of various natural and artificial polycyclic ethers. [reaction: see text]     

Synthesis and photochromic properties of novel yellow developing photochromic compounds

Two 1-thiazolyl-2-thienylcyclopentene derivatives, 1a and 2a, and a 1-thiazolyl-2-vinylcyclopentene derivative 3a have been synthesized in an attempt to obtain photochromic compounds which change the color from colorless to yellow, and have low photocycloreversion quantum yields and high absorption coefficients of the colored isomers. All of these compounds underwent reversible photochromic reactions. Compounds 1a and 2a in toluene solutions changed the color upon 313 nm light irradiation from colorless to orange and pink, in which absorption maxima were observed at 494 nm (ε=10,000 M⁻¹ cm⁻¹) and 525 nm (ε=8500 M⁻¹ cm⁻¹), respectively. On the other hand, the colorless toluene solution of 3a turned yellow upon irradiation with 313 nm light, in which the absorption maximum was observed at 416 nm (ε=17,100 M⁻¹ cm⁻¹). The photocyclization/cycloreversion quantum yields of 3 were 0.19 and 0.0014, respectively. The conversion from the open- to the closed-ring isomer of 3 in the photostationary state under irradiation with 313 nm light was close to 100%.     

One-step analysis of testis steroidogenesis from neonatal exposure to synthetic estrogen by normal-phase HPLC

Neonatal exposure to synthetic estrogen endocrine disruptors or estrogen-receptor inhibitors induces developmental abnormalities in the male reproductive system. To investigate whether neonatal exposure affects spermatogenesis in juvenile and pubertal testis, Sprague-Dawley rat pups were given synthetic estrogen endocrine disruptors or estrogen-receptor inhibitors by a single injection on the day of birth at concentrations ranging between 2 to 40 mm, and sacrificed on day 21 (juvenile), 35 (prepuberty) or 50 (puberty). The testes were weighed and examined histologically at each stage. Further, the metabolites of steroidogenesis were analyzed using normal-phase high performance liquid chromatography. Neonatal exposure significantly reduced testis weights and steroidogenesis to one- fifth to one-half of that of the juvenile control, and further suppressed irreversible steroidogenesis and spermatogenesis during puberty.     

Photochromism of triangle terthiophene derivatives as molecular re-router

2,2[prime or minute]-3,3[double prime]-Terthiophene derivatives undergo photochemically reversible cyclization and cycloreversion reactions. The absorption peak wavelength changed systematically with substitution of the phenyl rings at 5-, 5[prime or minute]- and 5[double prime]-positions of the thiophene rings, which indicates re-routing of the [small pi]-conjugation system.     

Synthesis and characterization of a magnetic semiconductor Na(2)RuO(4) containing one-dimensional chains of Ru(6+)

A new ternary ruthenium oxide Na(2)RuO(4) was prepared and shown to crystallize with a new structure type. Single crystal X-ray diffraction measurements reveal that Na(2)RuO(4) consists of RuO(4) chains made up of RuO(5) trigonal bipyramids by sharing axial corners. Na(2)RuO(4) is a magnetic semiconductor with a variable range hopping behavior, and its molar magnetic susceptibility chi(mol) has a broad maximum at approximately 74 K. The derivative d(chi(mol).T)/dT exhibits a peak at 37.7 K which has been confirmed by heat capacity measurement to be due to long-range antiferromagnetic ordering.