过渡金属催化的炔烃复分解反应

综述了过渡金属均相催化的炔烃复分解反应进展,主要分为两部分：一是炔烃复分解反应在炔烃合成中的应用,即从六、七十年代Mortreux催化剂的发现能均相催化炔烃的歧化反应,经过一系列的条件改造,合成了炔醚和二芳基乙炔等化合物,并提出了可能的两种机理：金属卡宾和金属卡拜机理;金属钼和钨的卡拜络合物相继合成,发现此类络合物能够催化官能化的二炔的复分解反应,合成一系列的大环化合物。二是炔烃复分解反应在合成高聚物中的应用,即钙和钨的卡拜络合物被用来催化ROMP和ADIMET反应合成高聚物,改良了的Mortreux催化剂也能催化高聚物的生成,这些高聚物在发光器件、有机"塑料"激光、液晶显示器上都有应用。     

Optimizing the preparation of an alumina-supported rhenium catalyst for olefin metathesis

The processes involved in the formation of the alumina-supported rhenium catalyst for olefin metathesis, from the impregnation of the support (thermally activated alumina) with ammonium perrhenate to thermal activation, are studied. The monolayer coverage of the Al₂O₃ surface is observed at a rhenium content of 10 wt % (on Re₂O₇ basis), and the surplus rhenium is sublimed as heptoxide from the support upon thermal activation. In the metathesis of both linear α-olefins and methylenecyclobutanes, the optimum supported rhenium content of the catalyst is 10 wt % on Re₂O₇ basis.     

One-pot three-component tandem metathesis/Diels-Alder reaction

[reaction: see text] A tandem enyne, diene-ene metathesis reaction followed by Diels-Alder reaction accomplished a stereoselective three-component reaction protocol with four stereocenters.     

Synthesis,structure, and activity of enhanced initiators for olefin metathesis

A series of ruthenium olefin metathesis catalysts of the general structure (H(2)IMes)(PR(3))(Cl)(2)Ru=CHPh (H(2)IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) have been prepared; these complexes are readily accessible in two steps from commercially available (H(2)IMes)(PCy(3))(Cl)(2)Ru=CHPh. Their phosphine dissociation rate constants (k(1)), relative rates of phosphine reassociation, and relative reaction rates in ring-opening metathesis polymerization (ROMP) and ring-closing metathesis (RCM) have been investigated. The rates of phosphine dissociation (initiation) from these complexes increase with decreasing phosphine donor strength. Complexes containing a triarylphosphine exhibit dramatically improved initiation relative to (H(2)IMes)(PCy(3))(Cl)(2)Ru=CHPh. Conversely, phosphine reassociation shows no direct correlation with phosphine electronics. In general, increased phosphine dissociation leads to faster olefin metathesis reaction rates, which is of direct significance to both organic and polymer metathesis processes.     

Synthesis of beta-bisabolol by ring-closing olefin metathesis reaction

A ring-closing olefin metathesis is the key step in the synthesis of the beta-bisabolols.     

Removing ruthenium residues from olefin metathesis reaction products

Olefin metathesis has revolutionized the way chemists design and synthesize molecules, mostly due to the development of well-defined ruthenium catalysts with high oxygen-, moisture-, and functional-group tolerance. However, the complete removal of residual ruthenium after the end of a metathesis reaction often imposes significant challenges. This Minireview summarizes the strategies for the sequestration of ruthenium impurities from olefin metathesis post-reaction mixtures, thus comprising a practical guide for synthetic chemists employing ruthenium-catalyzed metathesis reactions in the synthesis of organic or polymeric materials.     

Use of the olefin metathesis reaction for highly efficient β-cyclodextrin modification

A series of novel primary face mono-substituted β-cyclodextrin derivatives have been synthesised using the olefin metathesis reaction. Mono-6-allylamino-6-deoxy-β-cyclodextrin easily synthesised by nucleophilic substitution of mono-6-tosyl-β-cyclodextrin is the key synthon in the preparation of cyclodextrin derivatives mono-functionalised at the primary face by alkyl, aryl or perfluoroalkyl groups using Grubbs catalyst. In the cases of vinylbenzene and 1H,1H,2H-perfluoro-1-octene, the metathesis reactions yield with 95% stereoselectivity of the E-isomer.     

The metathesis reaction for side chain construction in carbocyclic sinefungin analogue synthesis

The naturally occurring nucleoside sinefungin has found considerable use in biological investigations. More extensive sinefungin studies have been limited because few analogues have been reported due to the synthetic challenges associated with such studies. Reported herein are preparative ways to two carbocyclic sinefungin analogues: 6′-deaminocarbocyclic sinefungin and (S)-6′-hydroxy-6′-deaminocarbocyclic sinefungin. The synthetic routes were made efficient and practical by the application of two metathesis reactions employing second generation Grubbs catalyst.     

Microwave enhanced Akabori reaction for peptide analysis

The Akabori reaction, devised in 1952 for the identification of C-terminus amino acids, involves the heating of a linear peptide in the presence of anhydrous hydrazine in a sealed tube for several hours. We report here a modified Akabori reaction that rapidly identifies the C-terminus amino acid in a polypeptide including its amino acid sequence information at both the C-terminus and the N-terminus. This modified methodology demonstrates the fundamentals of microwave chemistry applied to bioanalytical problems. In this modified process, hydrazinolysis has been accelerated by the application of microwave irradiation. In our reaction, the linear peptide and hydrazine solution, contained in a loosely covered conical flask, was exposed to a few minutes of irradiation using an unmodified domestic microwave oven. While the classical Akabori reaction required several hours, the microwave assisted reaction takes just minutes. If dimethyl sulfoxide is added to dilute the reaction mixture, the process is retarded enough to allow aliquots of the reaction mixture to be drawn every few minutes over a period of about an hour in order to study the progress of hydrazinolysis. Reaction products were monitored by mass spectrometry-primarily FAB-MS. In addition to providing sequence information, the microwave enhanced Akabori reaction quickly detects the presence of arginine (Arg) by converting each Arg to ornithine (Orn). Furthermore, certain amino acids, containing beta-SH, CO2H, and CONH2 groups in their side chain, are susceptible to modification by hydrazine, thereby, providing rapid confirmation of the presence of these amino acid residues. In these preliminary studies, the following oligopeptides were analyzed to demonstrate the effectiveness of our approach; the dipeptide (Trp-Phe), the tripeptide (Tyr-Gly-Gly), the tetrapeptide (Pro-Phe-Gly-Lys), the heptapeptide (Ala-Pro-Arg-Leu-Arg-Phe-Tyr), and a N-terminal blocked tripeptide (N-acetyl-Met-Leu-Phe).     

Automatic chiral selection in a thermodynamically predisposed metathesis reaction

[reaction: see text] Tryptophan-derived azoninoindole imines select partners of the same chirality for dimerization to helical macrocycles.     

Optimizing protein extraction from plant tissues for enhanced proteomics analysis

Plant tissues usually contain high levels of proteases and secondary metabolites that severely interfere with protein extraction, separation, and identification. Preparation of high-quality protein samples from plant tissues for proteomic analysis represents a great challenge. This article briefly describes the critical points in protein separation, especially secondary metabolites in plant tissues, and removal strategy. It provides an updated overview of three total protein extraction methods and their applications in proteomic analysis of various recalcitrant tissues.     

Grafting of arginine and glutamic acid onto cellulose for enhanced uranyl sorption

The grafting of arginine and glutamic acid on cellulose (through an intermediary step of chlorination) allows improving uranyl sorption of the biopolymer. The sorbents (Arg-Cell and Glu-Cell) were characterized by elemental analysis, FTIR spectrometry, XRD, SEM-EDX analysis and TGA. The sorption efficiency increases with pH; this can be attributed to the deprotonation of carboxylic acid and amine groups and to the formation of polynuclear hydrolyzed uranyl species. Sorption isotherms (fitted by the Langmuir equation) show sorption capacities at saturation of the monolayer of 147 and 168 mg U g^?1 for Arg-Cell and Glu-Cell, respectively (compared to 78 mg U g^?1 for raw cellulose); maximum sorption capacities at equilibrium (experimental values) reach 138, 160 and 73.4 for Arg-Cell, Glu-Cell and cellulose, respectively. Uranyl sorption is endothermic and is spontaneous for amino acid derivatives of cellulose (contrary to exothermic for cellulose). Uptake kinetics for the different sorbents are fitted by the pseudo-second-order rate equation. Uranium can be desorbed using sulfuric acid solutions, and the sorbents can be recycled for a minimum of five cycles of sorption/desorption: the decrease in sorption capacities at the fifth cycle does not exceed 13%.     

On the mechanism of a double ring-closing metathesis reaction

A detailed study of the steps involved in the double ring-closing metathesis reaction of 2 to 3 has been carried out. Both the selectivity and mechanism were affected by choice of catalyst.     

A simple aqueous metathesis reaction yields new lanthanide monothiophosphates

This paper describes the synthesis and characterization of two, new rare earth monothiophosphate materials, LaPO₃S·xH₂O and NdPO₃S·yH₂O, and their properties in comparison to the corresponding orthophosphates prepared by a similar aqueous metathesis reaction. Each of these new materials was found to exist in an amorphous phase similar to a corresponding orthophosphate mineral. The new rhabdophane-type oxythiophosphates were found to display reversible dehydration and rehydration under mild conditions. The materials were found to be thermally unstable. Disproportionation was found to occur at less than 450 °C under vacuum. Sulfur is lost during heating in air between 450 and 650 °C, according to thermogravimetric analysis (TGA) experiments, yielding the orthophosphate. The monothiophosphate hydrates display broad photoluminescence in the visible under excitation by a 325 nm laser. The compounds were also analyzed using differential thermal analysis, FT-IR and UV/vis/NIR spectroscopy.     

Misleading information on homogeneity and heterogeneity obtained from sorption isotherms

In this paper, the applications and the differences among the widely applied sorption isotherms (Langmuir isotherm for adsorption, competitive adsorption, ion exchange, Freundlich isotherm) are shown. The misleading information obtained by the formal applications of the isotherms is demonstrated using a simple mathematical model of homovalent ion exchange on homogeneous surface. This model calculation clearly reveals that when studying surface accumulation processes, the mechanism of the sorption process has to be determined. The correct thermodynamic interpretation of the data of sorption experiments is possible only if the isotherm is adapted to the sorption mechanism. It is emphasized that the regression values of the applied models themselves provide correct information neither on the surface heterogeneity nor the interactions among the sorbed species. The curved shape of an inadequate applied isotherm gives no information about the heterogeneity. In order to study the energy distribution of surface sites, the thermodynamic equations, including isotherms, has to be selected on the basis of sorption mechanism. All variable quantities involved in the given model (concentrations of the competing substances in all phases) have to be measured experimentally and included into the isotherm.     

Thermodynamics of naphthalene sorption to organoclays: role of surfactant packing density

Temperature dependence of naphthalene sorption to four organoclays with different surfactant (CTMA+) packing densities was examined. The results showed that both DeltaH o and DeltaS o increase generally with CTMA+ packing density. For organoclays with a low CTMA(+) packing density, the sorption process is driven by both the enthalpy term (DeltaH(o)) and the entropy term (-T DeltaS o), with values ranging from -4.7 to -7.5 kJ mol(-1) and -15.9 to -20.8 kJ mol(-1), respectively. As the CTMA+ packing density increases, the sorption process is driven by the entropy term (from -29.2 to -65.0 kJ mol(-1)) while it is opposed by the enthalpy term (from 7.9 to 40.5 kJ mol(-1)). These results indicate that the enthalpy demand for cavity formation within the surfactant aggregates and the mixing entropy of solute with surfactant aggregates both increase with the surfactant packing density. This means that the surfactant aggregates will form various organic phases as their packing density varies. Controlling the surfactant aggregates within an intermediate packing density range can improve the sorption capacities of the organoclays.     

A ring-fusion/ring-fission mechanism for the metathesis reaction of macrocyclic formaldehyde acetals

Important insight has been obtained into the mechanism of the reversible acid-catalysed transacetalation of cyclophane formaldehyde acetals (formals) C(i) in CDCl(3), at 25 degrees C. The order of appearance of the lowest oligomers in the early stages of the equilibration reaction is fully consistent with ring-fusion/ring-fission processes in which oxonium ion intermediates undergo S(N)2 reactions, according to an acid-catalysed bimolecular (A2) mechanism. The alternative acid-catalysed monomolecular (A1) reaction path, based on "back-biting" processes of carbenium ions generated by S(N)1-type cleavage of oxonium ion intermediates, predicts sequences that are in marked contrast with experimental findings.