Bifunctionalized allenes. Part XXII. Coinage metal-catalyzed cycloisomerization of phosphorylated 3-(α- or β-hydroxyalkyl)allenes to 2-phosphoryl-2,5-dihydrofurans or 2-phosphoryl-5,6-dihydro-2H-pyrans

Abstract

The present paper discusses the coinage metal-catalyzed cycloisomerization reaction of phosphorylated 3-(α- or β-hydroxyalkyl)allenes. 3-(α- or β-Hydroxyalkyl)-allenylphosphonates and -allenyl phosphine oxides were smoothly converted into the 2-phosphoryl-2,5-dihydrofurans or 2-phosphoryl-5,6-dihydro-2Н-pyrans by using 5?mol % of coinage metal salts as catalyst in 5-endo-trig or 6-endo-trig cycloisomerization, respectively. Experimental conditions such as the type of the solvent, the reaction temperature, the mol % and the type of the catalyst and its influence on the yields and the reaction time of the cycloisomerization reaction of the phosphorylated 3-(α- or β-hydroxyalkyl)allenes were optimized.     

What is so special about aerosol-OT? Part IV. Phenyl-tipped surfactants

Properties are reported for new phenyl-tipped anionic surfactants, which are aromatic chain relatives of the normal aliphatic aerosol-OT (AOT, sodium bis(2-ethyl-1-hexyl)sulfosuccinate). Variations in chain length and branching with these aromatic surfactants have important effects on aqueous and water-in-oil (w/o) microemulsion phase properties. In dilute aqueous systems, chain structure affects the cmc and surface tension behavior: compared to linear chain analogues, the branched-chain surfactants display lower surface tensions but also reduced packing as measured by molecular area at the cmc a(cmc). Owing to the phenyl-tipped structure, water-in-oil microemulsions were stabilized with aromatic toluene as an oil but not with aliphatic heptane; the latter is commonly used with normal AOT. Contrast variation small-angle neutron scattering (SANS) was used to characterize the microemulsion aggregates and adsorbed films. These SANS data show that water-in-toluene microemulsions stabilized by aromatic-AOTs contain mildly polydisperse spherical nanodroplets of similar structure to those found in systems containing normal AOT. Molecular areas at the air-water and toluene-water interfaces are found to be of similar magnitude and follow a trend that correlates with variations in surfactant chain structure. The new results with aromatic surfactants build on extensive studies of aliphatic AOT analogues (Nave, S.; Eastoe, J.; Penfold, J. Langmuir 2000, 16, 8733. Nave, S.; Eastoe, J.; Heenan, R. K.; Steytler, D.; Grillo, I. Langmuir 2002, 16, 8741. Nave, S.; Eastoe, J.; Heenan, R. K.; Steytler, D.; Grillo, I. 2002, 18, 1505), suggesting that the versatility of normal AOT originates from an optimized head and chain spacer group rather than from any specific effects of the 2-ethyhexyl chain structure.     

IrII(ethene): metal or carbon radical? Part II: oxygenation via iridium or direct oxygenation at ethene?

Treatment of [(Me3tpa)IrII(ethene)]2+ (Me(3)tpa =N,N,N-tri(6-methyl-2-pyridylmethyl)amine)(1(2+)) with dioxygen in weakly coordinating solvents results in formation of [(Me3tpa)IrIII(ethene)(superoxo)]2+ (4a2+). In the presence of DMPO (DMPO = 5,5-dimethyl-2-pyrrolidine-1-oxide) DMPO is substituted for ethene, and subsequently oxidized to DMPOX by the superoxo fragment to give [(Me3tpa)IrIII(DMPOX)]2+ (7(2+); DMPOX = 5,5-dimethyl-2-pyrrolidone-1-oxide). In acetonitrile, in the absence of DMPO, oxygenation of 1(2+) to [(Me3tpa)IrIII(formylmethyl)(MeCN)]2+ (2(2+)) is observed. In the presence of DMPO the formation of 2(2+) and 7(2+) is competing. Oxygenation of 1(2+) to 2(2+) may proceed via 4a(2+), involving an insertion mechanism at the metal. However, a mechanism based on olefin ligand non-innocence seems a reasonable alternative. This involves formation of acetonitrile adduct [(Me3tpa)Ir(ethene)(MeCN)]2+ (3(2+)), which has a significant metalla-ethyl radical (IrIII-CH2CH2*) character, allowing attack of 3O2 directly at the ethene ligand. Both pathways are discussed on the basis of experimental observations and DFT geometry optimizations.     

How does a reversible electrode respond in a.c. voltammetry? Part 2: solutions for the periodic current amplitudes

Journal of Solid State Electrochemistry - In a.c. voltammetry, a programmed electrical potential—a linear ramp modulated by a sine wave of frequency ω and modest amplitude—is...     

Stereoselective synthesis of α,α′-diamino-dicarboxylic acids. Part 2

Enantiomerically pure α,α′-diamino-dicarboxylic acids (R,R)-4, (S,S)-5 and (S,S)-7 have been synthesized starting from the glycine-derived chiral synthon (S,S)-1.     

Crystallographic and structural characterization of heterometallic platinum compounds. Part II. Heterobinuclear Pt compounds with Pt?M (M = transition or lantanide metal) > 3.0 ?

This review covers almost two hundred and twenty heterobinuclear platinum compounds in which Pt?M separation is over 3.0 ?. The M is a transition metal (Cu, Ag, Au, Ti, V, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni and Pd). There is an example of a lanthanide, Yb and a actinide, U. The Pt atom has oxidation numbers 0, +2 and +4. The Pt coordination geometries include trigonal planar Pt(0); square planar Pt(II); trigonal bipyramidal, and pseudo octahedral Pt(IV), with the most frequent being square planar. The most common ligands for Pt are P and C donor atoms, as well as a chlorine atom. The Pt ?? Ag distance of 3.002(1) ? is the shortest found in this series. There are examples which contain two crystallographically independent molecules, which differ mostly by degree of distortion and even one unique example, which contains eight such molecules. These are examples of distortion isomerism. Factors affecting bond lengths and angles are discussed and some ambiguities in coordination polyhedral are outlined.     

Strukturuntersuchungen an Paramyosin. 2. Mitt.: Ronfigurations?nderungen

Ohne Zusammenfassung     

Reactions COH2 en catalyse homogene. Hydrocarbonylation de butanols en presence de catalyseurs au cobalt et au ruthenium

The four butanols were converted into C₅ homologous alcohols in the presence of cobalt-ruthenium binary catalysts. The behaviour of each alcohol was examined against catalyst composition and promoting agent. The best results were obtained with Co/Ru molar ratios close to 5. The chain-lengthening mechanism is supposed to involve an olefinic intermediate (at least for s- and t-butanol) which is subsequently hydroformylated. The cocatalytic effect of ruthenium is, however, still unclear.     

The hydroperoxysulfonium ylide. An aberration or a ubiquitous intermediate?

An intramolecular isotope effect has been measured for the reaction of singlet oxygen with 2,2,8,8-tetradeuterio-1,5-dithiacyclooctane, 4d₄. The magnitude of the isotope effect, 1.21±0.09, provides verification of removal of an α-hydrogen during the product determining step to form a hydroperoxysulfonium ylide and ultimately the sulfoxide product. The absence of any special structural features in 4d₄ to enhance the propensity of hydrogen removal is used to suggest that the hydroperoxysulfonium ylide is a ubiquitous intermediate in the reactions of sulfides with singlet oxygen.     

Solution properties of octyl-β-D-glucoside. Part 2: Thermodynamics of micelle formation

Solution properties of octyl--D-glucoside have been examined in a wide temperature and concentration range, by means of freezing point depression, volumetric and calorimetric methods. Partial molal quantities and the variations consequent to micellization have been evaluated and discussed. Strong support to the hypothesis of a growth of the micellar aggregates was inferred from heat capacity findings.     

The Ti2H2 molecule: terminal or bridging hydrogens ?

Density functional calculations carried out for Ti₂H₂ show that several structures are thermodynamically stable with respect to Ti₂+H₂. The ground state of Ti₂H₂ is found to be ³B₁ and it involves two hydrogen bridges in a nonplanar C _{2 v} arrangement. The ¹A₁ state and other triplet states of the bridging structure are only a few kilocalories per mole above the ground state. The ¹Σ _g ⁺ state, which corresponds to the Ti analogue of acetylene, is energetically less favored than the bridging structure but it is still bound relative to Ti₂+H₂. Results are also presented for the Ti₂H molecule. Both bridging and terminal isomers are found to be very stable due to the formation of strong covalent Ti-H bonds. A comparison of the calculated harmonic vibrational frequencies and IR intensities of Ti₂H₂ and Ti₂H isomers with the spectra from matrix isolation IR studies on Ti _x /H₂ indicates that these molecules may have been produced in low-temperature reactions. Received: 15 September 1999 / Accepted: 7 December 1999 / Published online: 19 April 2000     

416 - Surface and/or donnan potentials at the thylakoid membrane?: Part III. Experimental results for a 1 : 1 electrolyte

The light-induced change of the transmembrane potential of spinach thylakoids is measured via the electrochromic absorption change, which is corrected for additionally occurring light-scattering changes. The potential is negligible for KCl concentrations > 5 × 10⁻² M, which suggests the interpretation as a generalized Donnan potential with constant internal volume. Accordingly, the variation of the dark volume with KCl concentration, which does occur and is measured by radioactive labelling of the water, cannot be described by an osmotic equilibrium with freely variable volume.     

Syntheses and Olfactory Characters of Some Endo-α-Substituted-Bicyclo[2. 2. 2]-Octenyl (or Octanyl) Methanols

Sixteen title compounds were synthesized, twelve of which are new ones. Their structures were determined by 1H NMR, IR and MS, the refractive indices or melting points were measured. Odors of all the title compounds were evaluated and the structure-odor relationship was briefly discussed.     

ChemInform Abstract: Computational Studies of Atmospheric Chemistry Species. Part 7. An ab initio Study of the N2×××O2 Heterodimer.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Synthesis of UDP-GalNAc analogues as probes for the study of polypeptide-α-GalNAc-transferases. Part 2

The synthesis of four UDP-GalNAc analogues (1-4) is described. The 3-, 4- and 6-deoxygenated analogues 1-3 were obtained by way of a divergent strategy starting from a 3,6-di-O-pivaloyl GlcNAc derivative as a common precursor. Analogue 4 bearing a N-trifluoroacetamido group was prepared from the trifluoromethylated oxazoline 24 as key intermediate. These compounds were designed to probe the substrate specificity of polypeptide-α-GalNAc transferases.