Synthesis of cyclicβ-silylenones via oxidative rearrangement of tertiaryα-hydroxy allylsilanes with PCC

An oxidative rearrangement of cyclic tertiary a-hydroxy allylsilanes has been carried out in refluxing ClCH₂CH₂Cl with pyridinium chlorochromate（PCC）.The reaction provides a convenient method to synthesize cyclicβ-silylenones in modest to excellent yields.     

Non-cross-linked polystyrene-supported triphenylarsonium halides and their use in the arsa-Wittig reaction

Non-cross-linked polystyrene-supported (carbomethoxymethyl)triphenylarsonium bromide (1) and benzyltriphenylarsonium iodide (2) were synthesized. They showed similar reactivities compared with the free arsonium salts in the arsa-Wittig reaction. The use of the polymer-supported reagents facilitated product purification and rendered the organoarsenic reagents easily separable and recyclable.     

含吡啶鎓阳离子的阴离子受体的研究进展

本文综述了近年来含吡啶鎓阳离子受体在阴离子识别领域的研究进展。系统阐述了以吡啶鎓阳离子为主要识别位点的环状、非环状和互锁型阴离子受体的设计合成以及在阴离子识别领域的应用。     

Pyridinium tribromide catalyzed condensation of indoles and aldehydes to form bisindolylalkanes

An efficient synthetic method for bis(indol-3-yl)alkane derivatives has been developed.In the presence of 5 mol%of pyridinium tribromide(PTB),the condensation of indoles and aldehydes proceeded smoothly under mild conditions,giving rise to the corresponding bis(indol-3-yl)alkanes in good to excellent yields.     

Formation and reactivity of gem-difluoro-substituted pyridinium ylides: Experimental and DFT investigation

According to DFT B3LYP/6-31G* calculations the reaction of difluorocarbene with pyridines proceeds reversibly with the formation of thermodynamically unstable intermediates, difluoro-substituted pyridinium ylides, which dissociate to carbene and pyridine with low activation barrier. The equilibrium constant of the reaction increases with increasing electron-withdrawing ability of substituents in the pyridine ring. Difluoroylides were generated from 4-cyano, 4-benzoyl- and 4-ethoxycarbonyl-substituted pyridines under difluorocarbene generation conditions (CF₂Br₂/Pb/Bu₄NBr/CH₂Cl₂/ultrasound) and trapped with dimethyl maleate or fumaronitrile. 3-Fluoroindolizines were isolated as final products of the reaction which involves dehydrofluorination of the primary cycloadducts followed by dehydrogenation by active MnO₂.     

TLC separation of some biologically important amino acids on pyridinium tungstoarsenate impregnated layers

Summary A satisfactory TLC separation scheme for 15 important amino acids on silica gel layers impregnated with pyridinium tungstoarsenate using isoamyl alcohol-wateracetic acid (605030) as the solvent system has been worked out. It is found that the Martin relationship is obeyed by similarly constituted amino acids. A plot of R_M vs the concentration of pyridinium ion released shows a scatter suggesting that, besides exchange properties, other factors also strongly influence the movement of amino acids.     

Regioselective halogenation of pyridinium N-(benzoazynyl) aminides as a way to produce N-benzyl-α-aminobenzoazines

The halogenation of pyridinium N-(benzoazynyl) aminides with N-halosuccinimides provides a mild and regioselective method to functionalize the negatively charged diazine moiety in most cases. In some examples, however, formation of other products is explained. Finally, alkylation of the exocyclic nitrogen and reduction of the N–N bond provides a simple and straightforward strategy to obtain functionalized N-benzyl-benzoazynyl-α-amines.     

The Iowa connection

A summary of the Fluorinated Ylide Chemistry, Organometallic Chemistry, Phosphonate Chemistry, Single-Electron-Transfer Chemistry and Metal Hydride Chemistry carried out at the University of Iowa is described.     

Triphenylphosphonioacetylide: A Species Isoelectronic with Isocyanides

Stabilized only by triphenylphosphane , the title compound 1 was synthesized and investigated theoretically (the HOMO of 1 is depicted on the right). Both calculations and experimental NMR spectra show that no Lewis structure can describe the geometry and charge distribution accurately. Compound 1 undergoes an equivalent of the Passerini reaction. Ph₃P⁺−C≡C⁻: 1     

Ylidaddukte der Penteltrichloride

Ylide Adducts of Pentele Trichlorides Ylides Ph₃PCR₂ form 1 : 1 adducts with PCl₃, AsCl₃ und SbCl₃. The addition of HCl to dichlorophosphanyl- und dichloroarsanyl ylides also leads to such adducts. In solution the PCl₃ adducts 2 are dissociated into ions. For the AsCl₃ adducts 3 b and 3 e of triphenylphosphonium ethylide and isopropylide X-ray analyses show distinctly different degrees of transition from a zwitterionic ψ-tbp to a cationic ψ-tetrahedral structure. The SbCl₃ adduct 4 b of the triphenylphosphonium ethylide on the other hand forms a rather asymmetric dimer and approaches a square-pyramidal geometry at the antimony atom. The 2 : 1 ylide adducts 11 with PCl₃ form in solution the dications (Ph₃PCR₂)₂PCl²⁺. The 2 : 3 adduct 15 of triphenylphosphonium methylide to AsCl₃ also has an ionic structure in the crystal. There are cations (Ph₃PCH₂)₂AsCl²⁺, which pairwise join with two AsCl₃ molecules to form doubly charged supracations in the presence of As₂Cl₈^2– as counterions.