1:1 Complexes of octafluoronaphthalene with trans-stilbene and trans-azobenzene

Co-crystallisation of octafluoronaphthalene (OFN) with trans-stilbene or trans-azobenzene from solutions yielded 1:1 molecular complexes, shown by single-crystal X-ray diffraction to contain infinite stacks of near-parallel and planar, alternating OFN and trans-stilbene or trans-azobenzene molecules.     

Terpolymerization of maleic anhydride, trans-stilbene and acrylic monomers

The results of radical terpolymerization of maleic anhydride (MA), trans-stilbene (Stb) and acrylic monomers (n-butyl methacrylate (BMA) and acrylonitrile (AN)) as acceptor-donor-acceptor monomer systems are discussed. The structure and composition of terpolymers are determined by chemical (acid number for MA units) and elemental (content of N for AN units and O for BMA units) analyses, as well as by FTIR spectroscopy through recorded analytical absorption bands for MA (1770 and 1845 cm⁻¹), Stb (864 cm⁻¹) and BMA (1730 cm⁻¹) units, respectively. The considerable change in the terpolymer compositions is observed when a strong acceptor MA is substituted with BMA (or AN), having comparatively low acceptor character in the system studied. Copolymerization constants for the MA ? Stb complex and acrylic comonomers pairs are determined according to the modified Kelen-Tüdös equation. Obtained results show that at the chosen ratios of comonomers, radical terpolymerization proceeded mainly by a true “complex” mechanism in the stage of near binary copolymerization of MA ? Stb complexed monomers with free BMA (or AN). The kinetics of terpolymerization and terpolymer compositions are studied in the low and high conversion stages. It is shown that for the MA-Stb-BMA system the dependence of R_p on the concentration of individual comonomers has extreme character, while for BMA-Stb-AN this dependence does not have similar character. This fact indicated that terpolymerization in the BMA-Stb-AN system proceeds according to a classical statistical copolymerization mechanism. The terpolymer composition-thermal behaviour relationships are also studied by differential scanning calorimetry and thermogravimetric analysis methods.     

Syntheses of tetraquinolinyl substituted pyrene, diphenylacetylene, and trans-stilbene ligands

We report the syntheses and characterizations of quinolinyl functionalized di-t-butyl-pyrene, diphenylacetylene, and trans-stilbene ligands.     

Radical ions and dianions of a cis-stilbene derivative that cannot isomerize into a trans form

A derivative of cis-stilbene which cannot be isomerized into a trans form may be reduced to the respective radical anions and dianions; the disproportionation rate of these radical anions (10⁸ M^?1 s^?1) and the respective equilibrium constant (≈ 8000) are exceedingly large.     

Enthalpies of reaction of bis(triphenylphosphine)(trans-stilbene)platinum(0) with diphenylcyclopropenone and benzocyclobutenedione

Enthalpies, ΔH(1) ?94.8 ± 6.0 and ΔH(6) ?57.1 ± 5.1 kJ mol^?1, of the following reactions have been measured calorimetrically [Pt(trans-stilbene)(PPh₃)₂](s) + dpcp(g) → (PPh₃)₂Pt(dpcb)(s) + trans-stilbene(g) (1) [Pt(trans-stilbene)(PPh₃)₂](s) + bcbd(g) → (PPh₃)₂Pt(bcpd)(s) + trans-stilbene (g) (6) where dpcp is diphenylcyclopropenone, (PPh₃)₂Pt(dpcb) is (1,1-bistriphenylphosphine)platinadiphenylcyclobutenone, (PPh₃)₂$\text{PtC(Ph)C(Ph)C}$O, bcbd is benzocyclobutene-1,2-dione and (PPh₃)₂Pt(bcpd) is (1,1-bistriphenylphosphine)platinabenzocyclopentanedione,

. It is concluded that the five-membered platinacyclo ring system in (PPh₃)₂Pt(dpcb) is not heavily strained.     

One-pot palladium-catalyzed highly chemo-, regio-, and stereoselective synthesis of trans-stilbene derivatives. A concise and convenient synthesis of resveratrol

A convenient, efficient and highly chemo-, regio-, and stereoselective one-flask synthetic method is reported for the construction of unsymmetrical (or symmetrical) trans-stilbene derivatives based on two sequential Heck-type reactions using tetraalkylammonium salt-based catalyst systems and vinyltrimethylsilane as double bond equivalents. Resveratrol has thus been concisely synthesized.     

Catalytic asymmetric dihydroxylation of substituted trans-stilbene derivatives: implications of the variation of enantioselectivities on the mechanism of OsO4 addition to olefins

The OsO₄ catalyzed asymmetric dihydroxylation of substituted trans-stilbene derivatives using 9-O-acetyldihydrocinchonidine as chiral ligand gives the corresponding diols with lower enantioselectivity in the case of substrates containing electron-donating and electron-withdrawing substituents. The Hammett correlations of the enantiomeric ratios exhibit non-linear plots, in accordance with the conclusion that the reaction involves a 1,3-dipolar type [3+2] cycloaddition transition state.     

Vibrational spectra of cis-stilbene and 1,1-diphenylethene

Raman and IR spectra of the named compounds have been measured as liquids at room temperature and as solids at low temperature. Some bands are shown to arise from atomic displacements essentially localised on the weakly interacting phenyl groups; symmetric and anti-symmetric combinations of these “phenyl modes” are almost degenerate and become appreciably mixed in some cases leading to anomalous values for their depolarisation ratios. Other modes, largely involving the ethylenic group, are identified and provide information concerning the molecular conformation in the liquid; both molecules have C₂ molecular symmetry. The low-temperature spectra are sharp and contain information about the crystal structures.     

The formal total synthesis of dragmacidin B, trans-dragmacidin C, and cis- and trans-dihydrohamacanthins A

A facile formal total synthesis of dragmacidin B, trans-dragmacidin C, and cis- and trans-dihydrohamacanthins A is presented. Our approach to these bis(indole) alkaloids involves a one-pot, four-step cross-coupling/deprotection sequence where complete halogen selectivity is observed. A related approach to access the dihydrohamacanthins is also described.     

Crystallizable trans-tactic copolyalkenamers

Random, essentially trans copolyalkenamers, obtained by ring opening copolymerization of cyclo-olefins in the presence of a metathesis catalyst, exhibit X-ray crystallinity. Interpretation of the X-ray fibre spectra indicates mutual isomorphous replacement of trans alkenamer units of widely different length in the crystal lattice, resulting in lowering of melting temperatures and degrees of crystallinity of the copolymers as compared to the corresponding homopolyalkenamers.     

The spirooxirane route to trans-fused γ-lactones

Convenient access to $\text{trans}$-fused γ-lactones is provided by sodium benzenethiolate promoted ring opening of appropriate γ,δ-spiroepoxyesters.     

Characterization of the photoisomers from cis- and trans-chlordanes, trans-nonachlor and heptachlor epoxide

Irradiation of acetone solutions of trans-chlordane (4a) and trans-nonachlor (4b) with UV light produces new half-cage photoisomers (5a or 6a and 5b or 6b, respectively) with bridging that differs from that of the photoisomers (2 and 8a) obtained from cis-chlordane (1b) and heptachlor epoxide (7). A new photoisomer (10) obtained from heptachlor epoxide is transformed into photoisomer 8a on further irradiation. Detailed PMR and ¹³C-NMR studies establish the structures of the new photoisomers and permit a decision between alternative formulations for the structures of the half-cage photoisomers of heptachlor epoxide and cis-chlordane,     

The synthesis of single enantiomers of trans-alkene-containing mycolic acids

We report routes to single enantiomers of hydroxy and ketomycolic acids containing an α-methyl-trans-alkene unit.     

The conformation and vibrational spectra of trans-1,4-dicyanocyclohexane

The IR spectra of trans-1,4-dicyanocyclohexane as a melt, as a solute in various solvents, as KI and polyethylene pellets and as amorphous and annealed crystalline solids at 90 K have been recorded in the region 4000-50 cm^?1. Additional spectra at high pressures (1–50 kbar) have been recorded and the dichroic ratios of oriented polycrystalline films are obtained above 200 cm^?1. Raman spectra of the compound as a melt, as an amorphous and crystalline solid at 90 K and dissolved in acetone, chloroform and benzene have also been recorded.The compound exists as an equilibrium mixture of ee and aa conformers in solution, in the melt and in the amorphous solid at 90 K, but as one conformer only, apparently the ee form, in the crystalline state. Unlike the corresponding dihalocyclohexanes, trans-1,4-dicyanocyclohexane cannot be converted to an “aa crystal” either by exposure to high pressure or by annealing to a metastable crystal.The fundamental frequencies of both conformers have been interpreted in terms of C_2h molecular symmetry and the assignments supported with a force constant calculation by the overlay technique transferring force constants from various related molecules.     

Synthesis of the trans-fusarinine scaffold

The trans-fusarinine backbone is a common feature encountered in many fungal siderophores. This monomer is notably the structural base of N^α-methyl coprogen B and dimerumic acid. Both siderophores are known to be secreted by Scedosporium apiospermum, an emerging pathogenic fungus studied for its high involvement in invasive infections of immunocompromised patients. The strategy developed here for the synthesis of the trans-fusarinine scaffold relies on the preparation of both N-hydroxyornithine and 3-anhydroxymevalonic acid subunits starting from l-ornithine and 3-butyn-1-ol, respectively. The coupling of these two building blocks led to the expected protected backbone.     

The photophysics and photobiology of the eye

The eye consists of three major segments: the cornea, lens and retina. The main function of the anterior ocular tissue, the cornea and the lens is to transmit and focus light on the retina without distortion. They also filter out UV light (less than 400 nm) and prevent it from reaching the retina. Much of the light reaching the retina is used for sight. However, light can have numerous other effects on the constituents of the eye, both beneficial and deleterious. This article reviews the interaction of light with the eye, various protective mechanisms, the possible role of light in aging and disease states and the role of light in biological processes other than sight such as mood, hormonal secretions and the cyclic growth and phagocytosis of the rods and cones.     

Stereoselective synthesis of highly substituted trans-2,3-dihydrofuran and trans-1,2-cyclopropane derivatives containing sulfonyl groups

trans-2,3-Dihydrofuran derivatives 3 and trans-1,2-cyclopropane derivatives 4 were prepared with high chemoselectivity and moderate overall chemical yield by the reaction of α,β-unsaturated sulfones 1 with arsonium bromides 2 in the presence of potassium carbonate. The structures of products obtained were identified by IR, MS, ¹H NMR, elemental analysis, and X-ray diffraction analysis.     

An efficient and highly stereoselective approach to trans-2,5-disubstituted-tetrahydrofuran and trans-2,6-disubstituted-tetrahydropyran derivatives

Bis-epoxides were converted into trans-2,5-disubstituted-tetrahydrofuran and trans-2,6-disubstituted-tetrahydropyran derivatives using a kinetic resolution followed by cyclization, in an efficient and highly enantio- and diastereoselective manner.