Photoaddition reactions of azomethine ylides generated from α-aminonitriles to fullerene C60: Formation of fulleropyrrolidines and reaction efficiencies changes depending on reaction conditions

Photoaddition reactions of C₆₀ with both (trimethylsilyl)methyl and either benzyl or phenethyl group containing α-aminonitriles were carried out to explore how product distributions and reaction efficiencies can be influenced by reaction solvent systems. The results show that photoreactions produce both trimethylsilyl- and cyano group containing fulleropyrrolidines as a major (or exclusive) product. Especially, photoreactions performed in either EtOH containing solution or oxygenated environment take place with a much more efficient manner.     

Silylated and germylated cyclopropanones

The synthesis of trimethylsilyl- and germyl-cyclopropanones, by treating diazomethane with the corresponding trimethyl ketene, and their ring expansion to cyclobutanones are described.     

Organometallphosphin-substituierte Übergangsmetallkomplexe. XXIII. Pentacarbonyl(organometallphosphin)chrom-, -molybdän-und -wolfram-Komplexe

Organometalphosphine Substituted Transition Metal Complexes. XXIII. Pentacarbonyl(organometalphosphine)chromium, Molybdenum, and Tungsten Complexes Hexacarbonyl-chromium, -molybdenum and -tungsten react under u.v. irradiation with tri(tert-butyl)-phosphine, di(tert-butyl)trimethylsilyl-, -germyl- and -stannylphosphine, tert-butylbis(trimethylsilyl-, -germyl- and -stannyl)phosphine as well as with tris(trimethylsilyl-, -germyl- and -stannyl)phosphine with displacement of one CO ligand and formation of the corresponding pentacarbonyl-organometalphosphine chromium, molybdenum and tungsten complexes. The i.r., Raman, ¹H n.m.r., and ³¹P n.m.r. spectra of the complexes are discussed.     

Preparation of unsymmetrical terphenyls via the nickel-catalyzed cross-coupling of alkyl biphenylsulfonates with aryl Grignard reagents

Unsymmetrical terphenyl derivatives were prepared by sequential transition metal-catalyzed cross-coupling reactions of neopentyl bromobenzenesulfonates with arylboronic acids and arylmagnesium bromides in good yields. Biphenylsulfonates undergo nickel-catalyzed coupling reactions more rapidly than the corresponding benzenesulfonates. The stepwise palladium- and nickel-catalyzed reaction of the bromobenzenesulfonates appears to be a promising and conceptually straightforward route for preparing unsymmetrical terphenyls.     

Synthesis and properties of homo- and copolymers of trifluoropropyldimethylsilyl-1-propyne with trimethylsilyl-1-propyne

Homopolymerization of 1-(3,3,3-trifluoropropyldimethylsilyl)-1-propyne is investigated in the presence of catalysts based on tantalum (V) chloride and niobium (V) pentachloride with various cocatalysts. As a result of homopolymerization, an insoluble polymer is formed. It is established that the insolubility of the homopolymer is connected with the presence in the polymer of “pseudocrystalline” regions playing the role of physical links. Copolymerization of 1(3,3,3-trifluoropropyldimethylsilyl)-1-propyne and trimethylsilyl-1-propyne under the action of the TaCl₅-Ph₃Bi system is studied. The relative activity constants of monomers, whose ratio points to the formation tendency of copolymers enriched with trimethylsilyl-1-propyne at the early stages of polymerization, are estimated. It is shown that the structures and solubilities of the obtained copolymers depend on their compositions. Gas-transport and hydrophobic-hydrophilic properties for soluble samples are studied. Soluble copolymers have good film-forming properties, improved hydrophobicity, stability against hydrocarbons, and high levels of gas permeability: properties that make them promising materials for the separation of various liquids and gaseous water-organic media.     

Competition between superexchange-mediated and sequential electron transfer in a bridged donor-acceptor system

The temperature- and solvent-dependence of photoinduced electron-transfer reactions in a porphyrin-based donor-bridge-acceptor (DBA) system is studied by fluorescence and transient absorption spectroscopy. Two competing processes occur: sequential and direct superexchange-mediated electron transfer. In a weakly polar solvent (2-methyltetrahydrofuran), only direct electron transfer from the excited donor to the appended acceptor is observed, and this process has weak temperature dependence. In polar solvents (butyronitrile and dimethylformamide), both processes are observed and the sequential electron transfer shows strong temperature dependence. In systems where both electron transfer processes are observed, the long-range superexchange-mediated process is more than two times faster than the sequential process, even though the donor-acceptor distance is significantly larger in the former case.     

Vibronic surprisal analysis of the dynamics of photodissociation and related reactions

Comparisons of experimentally observed product vibronic state distributions to statistically expected distributions indicate that intrafragment dynamics have primary importance in photodissociative and predissociative excitation reactions and in collision-induced electronic-to-vibrational energy transfer processes and that collisional dissociative excitation reactions probably involve sequential 2-body interactions rather than a concerted 3-body interaction.     

Steric effects in 29Si and 13C NMR spectra of trimethylsilyl- and alkyl-substituted benzenes

²⁹Si and ¹³C NMR spectra of trimethylsilylbenzenes substituted at different positions by methyl and trimethylsilyl groups were investigated with special reference to steric interactions between the ortho-substituents. The steric effects, as measured by ¹³C and ²⁹Si chemical shifts, are generally smaller in trimethylsilyl- than in t-butyl-substituted compounds. Both nuclei follow the same general trends in the benzene derivatives.     

Zur bildung metallacyclischer fünfringverbindungen: regioselektivität der addition von alkinen an zirconocenkomplexe

Metallacycles are formed upon thermolysis of (s-trans-η⁴-butadiene)zirconocene and binuclear (η²-aldehyde)zirconocene complexes or photolysis of diphenylzirconocene in the presence of t-butyl-, trimethylsilyl-, and phenyl-acetylene. From a surprising equally high preference for α-t-butyl- and -trimethylsilyl-substituted products as well as the statistically favoured 2,4-disubstituted metallacyclopentadienes formed from t-butyl- or trimethylsilyl-acetylene it is suggested, that the position of the substituents in the final product is predominantly determined by the coordination of the alkyne preceding the ring-closure reaction. In contrast to the thermally induced reactions the expected major product (2,5-disubstituted zirconacyclopentadiene) of the kinetically controlled cyclization reaction is formed upon photolysis of diphenylzirconocene in the presence of phenylacetylene.     

Sequential one-pot combination of multi-component and multi-catalysis cascade reactions: an emerging technology in organic synthesis

Creating sequential one-pot combinations of multi-component reactions (MCRs) and multi-catalysis cascade (MCC) reactions is a challenging task that has already emerged as a new technology in synthetic organic chemistry. Through one-pot sequential combination of MCRs/MCC reactions, the chemical products (fine chemicals, agrochemicals and pharmaceuticals) that add value to our lives can be produced with less waste and greater economic benefits. Within this Emerging Area, we describe our recent developments and designs for sequential one-pot MCRs/MCC reactions to facilitate their realization as biomimetics in organic chemistry.     

Synthesis and characterization of covalently linked multilayer films prepared in the absence of solvent

We report the preparation of multilayer organic thin films prepared by sequential vapor-phase coupling of monomers. The reactions were carried out at room temperature and atmospheric pressure. Films prepared using up to six sequential coupling reactions are reported. The following specific vapor-phase reactions were found to be viable: reactions between acid chlorides and both aliphatic and aromatic amine, hydrolysis reactions, anhydride activation, and reactions between anhydrides and primary amines. Homobifunctionalized monomers, such as hexamethylenediamine, react primarily via a single endgroup rather than cross coupling to the reactive surface via both reactive groups. The estimated coverage of the multilayer films is between 36 and 46%. The films were characterized using ellipsometric, contact angle, and spectroscopic measurements.     

Structurally diagnostic ion/molecule reactions: class and functional-group identification by mass spectrometry

This article discusses the application of gas-phase ion/molecule reactions for fine structural elucidation in mass spectrometry. This approach is illustrated via a representative collection of class- and functional group-selective reactions, a few of historical relevance as well as by more recent and instructive examples, and their applications. The focus is on reactions performed under well-controlled conditions of sequential mass spectrometry, discussing key mechanistic details and potential applications. Recent and innovative strategies that allow these reactions to be performed under ambient conditions, making this fast, selective and sensitive approach for structural investigation much more generally applicable, are also discussed.     

Rearrangement of α-acyloxyacetates into 2-hydroxy-3-ketoesters

α-Acyloxyacetates rearrange under LDA conditions to give 2-hydroxy-3-ketoesters. The corresponding trimethylsilyl- or acetyl derivatives can be obtained by quenching the reaction mixture with Me₃SiCl or Ac₂O.     

Capillary Columns with a Sorbent Based on Functionalized Poly(1-Trimethylsilyl-1-Propyne) for the Elution Analysis of Natural Gas

Russian Journal of Physical Chemistry A - The chromatographic properties of capillary columns prepared using functionalized poly(1- trimethylsilyl-1-propyne) (PTMSP) are evaluated and compared with...     

Sequential adsorption of bacteriophage T4 lysozyme stability variants at solid–water interfaces

The sequential adsorption of the wild type T4 lysozyme and one of its structural stability variants was studied, using ellipsometry and ¹²⁵I radioisotope labeling techniques. The mutant lysozyme was produced by substitution of the isoleucine residue at position 3 in the wild type with a tryptophan residue, resulting in a protein with lower structural stability. The mutant protein was more resistant to surfactant-mediated elution, and apparently adsorbed at the interfaces with a greater interfacial area/molecule than the wild typeT4 lysozyme. However, the results of each type of experiment suggested that sequential adsorption and exchange of proteins occurred only in the case of the less stable mutant followed by the wild type. This suggests that, in these exchange reactions, properties of the adsorbing protein (e.g. its ability to adsorb when a relatively small amount of unoccupied area is present) were more important than the apparent binding strength of the adsorbed protein molecules.     

Origin of miscibility‐induced sequential reordering and crystallization‐induced sequential reordering in binary copolyesters: a Monte Carlo simulation

The effect of the repulsive interaction between the components of binary copolyesters on their sequence order was investigated with the Monte Carlo simulation method. The phase separation and ester‐interchange reactions were implemented simultaneously with a kind of one‐site bond fluctuation model. When the repulsive interaction energy was applied to the binary copolyesters, miscibility‐induced sequential reordering (MISR) was induced. The more repulsive the pair interaction was, the higher the sequence order was. During the MISR process, homoester‐interchange reactions became more favorable because of the repulsive interaction, accompanying the decrease of the interactional free energy. The sequence order resulting from MISR was independent of the relative trial ratio of phase separation to ester‐interchange reaction at a given value of interaction energy. Restoration of the sequence distribution was also simulated with and without the repulsive interaction between the components of the binary copolyesters to investigate the effect of MISR on the crystallization‐induced sequential reordering (CISR) process in binary copolyesters, where sequences with lengths longer than 6 were assumed to crystallize and could not take part in ester‐interchange reactions. The sequence distribution in the amorphous phase was restored via ester‐interchange reactions. When the repulsive interaction was applied to binary copolyesters during the CISR process, restoration of the sequence distribution was accelerated, indicating that MISR can accelerate the CISR process when a polyester blend shows upper critical solution temperature behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1337–1347, 2001     

Synthese und reaktionen von element-IVB-substituierten stannacyclohexadienderivaten

Metallation of 1,1-dibutyl-1-stannacyclohexadiene-2,5 (I) with lithiumamides yield the lithium compound II, from which the trimethylsilyl-, germyl-, -stannyl- and the bromoethyl-substituted stannacyclohexadienes III, IV, V and VI are obtained. The bis(trimethylsilyl- and -germyl) substituted stannacyclohexadienes VIII and X have been synthesized starting from III and IV, respectively. Arsabenzene (XII) is formed in good yields by treating arsenic trichloride with III, IV and V. 4-Trimethylsilyl-1-arsabenzene (XIII), 4-trimethylgermyl1-arsabenzene (XIV) and 4-(2-chloroethyl)-1-arsabenzene (XV) can be prepared by treating VIII, X and VI respectively with arsenic trichloride, ¹H NMR, IR, UV and mass spectral data of the new compounds are described.     

Beta-lactam-forming photochemical reactions of N-trimethylsilylmethyl- and N-tributylstannylmethyl-substituted alpha-ketoamides

Two mechanisms have been proposed for the beta-lactam-forming photochemical reactions of alpha-ketoamides. One, suggested by Aoyama, involves excited-state H-atom abstraction while the other, put forth by Whitten, follows a sequential SET-proton-transfer route. The photochemical properties of N-trimethylsilylmethyl- and N-tributylstannylmethyl-substituted alpha-ketoamides were explored in order to gain information about the mechanism of this process and to develop a regioselective method for beta-lactam formation. The results of this effort show that (1) photoreactions of N-trimethylsilylmethyl-substituted alpha-ketoamides proceed by competitive H-atom abstraction and sequential SET-desilylation pathways and (2) a sequential SET-destannylation pathway is preferentially followed in photochemical reactions of the tributylstannylmethyl-substituted alpha-ketoamides.     

Thiolytic chemistry of alternative precursors to the major metabolite of the cancer chemopreventive oltipraz

The compounds 7-methyl-6,8-bis(methyldisulfanyl)pyrrolo[1,2-a]pyrazine (5; "bis disulfide") and methanethiosulfonic acid S-((6-(methanesulfonylsulfanyl)-7-methyl)pyrrolo[1,2-a]pyrazin-8-yl) ester (6; "bis methanesulfonic acid thioester") have been synthesized to serve as alternative precursors to the major metabolite, 4, of the cancer chemopreventive oltipraz, 1, to test whether they possess similar biological activities. In the present work the mechanisms by which these compounds react with glutathione have been investigated in order to validate the assumption that they would be chemically competent in the presence of the biological thiols to give the oltipraz metabolite. A kinetic and product study was carried out in mainly aqueous media, 相似文献   

Application of capillary electrophoresis-mass spectrometry to synthetic in vitro glycolysis studies

We propose an approach designed to reconstitute a metabolic pathway composed of multistep biochemical reactions, rather than to dissect the individual reactions that make up the pathway. A synthetic in vitro glycolysis was reconstructed from ten purified Escherichia coli (E. coli) enzymes to obtain a better understanding of the regulation of sequential enzymatic reactions. The key to the success of this approach is the ability to perform direct and simultaneous determination of the diverse metabolic intermediates in the pathway by capillary electrophoresis-mass spectrometry. We observed that the pathway is regulated by a delicate balance between the changing metabolite concentrations and behaves like a natural biological oscillating network that has hitherto not been reported for E. coli glycolysis. The end-product, pyruvate, was periodically synthesized from glucose at an overall efficiency of 30%, corresponding to an average of 90% conversion efficiency for each of the ten steps involved. This approach is likely useful for the synthesis of natural products requiring complex sequential biocatalytic reactions.