Synthesis of tetrasubstituted thiophenes from pyridinium 1,4-zwitterionic thiolates and modified activated alkynes

Pyridinium 1,4-zwitterionic thiolates were applied to a formal [3 + 2] annulation reaction with modified activated alkynes, affording various tetrasubstituted thiophenes with aryl, alkenyl, alkyl or silyl group at the special position. The structural modification of alkyne substrates enabled the synthesis of diverse thiophenes to be achieved using the pyridinium 1,4-zwitterionic thiolates as the sulfur-containing building blocks. This approach is metal-free and catalyst-free.     

“暗流体”简介

关于暗流体(Dark fluid)的提出,还要从两个星系团内明、暗物质的分布谈起:子弹星系团在中心发光物质的两侧分布着引力很强的暗物质,而Abell520星系团所显示的景象则是一个被热气体环绕着的暗物质核心,但其周围却不见普通星系的踪迹.     

Abundant Intramolecular Ring Rearrangements of 1-(N-Benzyloxycarbonylamino)arylmethylphosphonate Phenyl monoesters Under Electrospray Ionization Conditions

Abstract

The mass spectrometric behavior of 1-(N-benzyloxycarbonylamino)arylmethyl-phosphonate phenyl monoesters was investigated under positive ion electrospray ionization conditions. All nitrogen-protonated title compounds undergo four- and/or six-membered ring rearrangements to yield nitrogen-containing fragment ions by consecutive or simultaneous loss of a carbon dioxide and phenyl hydrogen phosphonate or phenyl benzylphosphonate or an arylmethylimine. All oxygen-protonated title compounds undergo four- to six-membered ring rearrangements to produce fragment ions by loss of a carbon dioxide plus an arylmethylimine, or phenyl benzylphosphonate, by consecutive or simultaneous loss of benzyl phenyl ether and isocyanic acid. The fragmentation is obviously different from the corresponding methyl and ethyl monoesters, which show a tendency to undergo intramolecular four-membered ring rearrangements only.

GRAPHICAL ABSTRACT      

Single-Ion Conduction and Electrochemical Characteristics of Poly (Oxyethylene)/ Lithium Methoxy Oligo(Oxyethylene) Sulfate Blend

Abstract

The ion conduction of a blend of poly(oxyethylene) (PEO) and lithium methoxy oligo(oxyethylene) sulfate (SAL₈) and its electrochemical characteristics were studied. The maximum ambient conductivity of the blend reaches 1.2 × 10^?6 S/cm. The blend exhibits single-ion conduction, excellent mechanical performance, and electrochemical stability. A battery of Li/PEO + SAL₈/Li_1+xV₃O₈ has a constant discharge capacity at different discharge current densities up to a certain voltage, while the discharge capacity of Li/P (MEO_16-AM) + LiClO₄/Li_1+xV₃O₈ decreases with an increase of the discharge current density.     

Synthesis, structure, and activity evaluation of two silver(I) complexes as Helicobacter pylori urease inhibitors

Two silver(I) compounds, [Ag(R,R-hxn)](C₇H₄BrO₂) · 2H₂O (I) (Chxn = 1,2-diaminocyclohexane) and [Ag(C₅H₆N₂)₂]₂(C₈H₄O₄) · 10H₂O (II), were synthesized and complex I was structurally characterized by X-ray crystallography. Compound I contains a catena-(trans-1,2-diaminocyclohexane) silver polycation ([Ag(Chxn)]_∞) in a roughly linear fashion, while II possesses a linear-type silver monocation. Compounds I and II were evaluated for their inhibitory activities against Helicobacter pylori urease in vitro. Both were found to have strong inhibitory activities against H. pylori urease comparable to that of acetohydroxamic acid.     

Composition heterogeneity of tetrafluoroethylene-hexafluoropropylene random copolymers characterized by successive self-nucleation and annealing

In the present work, successive self-nucleation and annealing (SSA) was applied to a series of tetrafluoroethylene-hexafluoropropylene random copolymers (FEPs). Multiple melting peaks were observed for all FEP samples after SSA thermal treatment. The lamellar crystal thicknesses were calculated from the melting temperatures, and the mass percentages of the crystals of specific thickness were obtained from the areas of the melting peaks. As a result, distributions of the lamellar thickness, which can be correlated to the composition distribution, were determined. It was found that the composition distribution of the FEP samples tended to become more heterogeneous as the content of hexafluoropropylene (HFP) comonomer increases. Samples with the same HFP content might also have different composition distributions.     

Efficient synthesis of unsymmetrical diaryl thioethers via TBAF-mediated denitrative substitution of nitroarenes with PhSTMS under mild and neutral conditions

Tetrabutylammonium fluoride(TBAF) effectively facilitated a denitrative substitution reaction of electron-deficient nitroarenes with phenylthiotrimethylsilane(PhSTMS) under mild and base-free neutral conditions at room temperature,providing a practical and efficient synthesis of useful unsymmetrical diaryl thioethers.Nitroarenes bearing ortho-and para-positioned electron-withdrawing groups are the most reactive substrates,indicating that this reaction most possibly proceeded via the nucleophilic aromatic substitution(S_NAr) mechanism.     

Theoretical studies on selectivities in the Staudinger reaction of vicinal diimines and ketenes

The selectivities,including peri-,regio-,and diastereoselectivities,in the Staudinger reaction involving vicinal diimines and ketenes were investigated theoretically via the density functional theory(DFT) calculation.The results indicate that vicinal diimines prefer stepwise [2+2] cycloaddition rather than [2+4] cycloaddition to generate cis-4-imino-β-lactams.The diimines attack the less sterically hindered exo-side of ketenes to generate zwitterionic intermediates,which directly undergo a conrotatory ring closure to produce cis-4-imino-β-lactams whatever diimines with less or more bulky N-substituents.For unsymmetric vicinal ketoaldehyde-derived diimines,their ketimines attack the exo-side of ketenes and undergo a conrotatory ring closure to produce cis-4-aldimino-β-lactams due to less steric effect.The current theoretical studies provide very important information for in-depth understanding of the selective formation of mono-cis-β-lactams from vicinal diimines and ketenes.