Reaction Leading (reaction + leading)

Distribution by Scientific Domains

Selected Abstracts

ChemInform Abstract: A New Domino Autocatalytic Reaction Leading to Polyfunctionalized Spiro[5.5]undecanes and Dispiro[]pentadecanes.

CHEMINFORM, Issue 40 2009
Bo Jiang
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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. [source]

ChemInform Abstract: Palladium-Catalyzed Chloroimination of Imidoyl Chlorides to a Triple Bond: An Intramolecular Reaction Leading to 4-Chloroquinolines.

CHEMINFORM, Issue 46 2008
Akira Isobe
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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. [source]

Metal-Promoted Variants of the Passerini Reaction Leading to Functionalized Heterocycles.

CHEMINFORM, Issue 38 2002
Qian Xia
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Preparation of Enantiopure Butane-2,3-diacetals of Glycolic Acid and Alkylation Reactions Leading to ,-Hydroxyacid and Amide Derivatives.

CHEMINFORM, Issue 15 2005
Steven V. Ley
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Two Successive One-Pot Reactions Leading to the Expeditious Synthesis of (-)-Centrolobine.

CHEMINFORM, Issue 50 2004
Lucie Boulard
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

BiCl3 -Catalyzed Diastereoselective Intramolecular [4 + 2] Cycloaddition Reactions Leading to Pyrazole Annulated New Sulfur Heterocycles (III).

CHEMINFORM, Issue 50 2003
Gowravaram Sabitha
No abstract is available for this article. [source]

Recovery of normal autologous myelopoiesis after graft rejection following allogeneic bone marrow transplant for agnogenic myeloid metaplasia

Summary Allogeneic hematopoietic transplantation is the only currently available therapy that has the potential to cure agnogenic myeloid metaplasia (AMM) or primary myelofibrosis (PMF). Amelioration of fibrosis and eradication of the abnormal clone is thought to occur through the repopulation of marrow by donor-derived hematopoiesis and graft- vs. -host reaction leading to graft vs. tumor effect. We report here a 50-year-old female with AMM/PMF, conditioned with busulfan and cyclophosphamide, who rejected a single locus (HLA-B) mismatched bone marrow transplant from her daughter, but recovered normal autologous hematopoiesis with disappearance of marrow fibrosis and extramedullary hematopoiesis. Variable number tandem repeats (VNTR) analysis showed a gradual loss of donor-derived hematopoietic cells with recovery of autologous hematopoiesis. This case therefore illustrates that eradication of AMM/PMF in this patient with myeloablative chemotherapy combined with a transient allogeneic effect was sufficient to suppress the abnormal stem cell clone associated with AMM/PMF with subsequent cure. [source]

Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reaction

Pedro Braña
Abstract The potential energy surface for the Cl + propene reaction was analyzed at the MP2 level using Pople's 6-31G(d,p) and 6-311+G(d,p), and Dunning's cc-pVDZ and aug-cc-pVDZ basis sets. Two different channels for the addition reaction leading to chloroalkyl radicals and five alternative channels for the abstraction reaction leading to C3H + HCl were explored. The corresponding energy profiles were computed at the QCISD(T)/aug-cc-pVDZ//MP2/aug-cc-pVDZ level of theory. Theoretical results suggest that the previously established mechanism consisting of (1) direct abstraction and (2) addition,elimination steps is instead made up of (1) addition through an intermediate and (2) two-step abstraction processes. No direct abstraction mechanism exists on the potential energy surface. The kinetic equations derived for the new mechanism are consistent with the pressure dependence experimentally observed for this reaction. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 2044,2062, 2003 [source]

Catalytic synthesis of styryl-capped isotactic polypropylenes

Huahua Huang
Abstract Bis-styrenic molecules, 1,4-divinylbenzene (DVB) and 1,2-bis(4-vinylphenyl)ethane (BVPE), were successfully combined with hydrogen (H2) to form consecutive chain transfer complexes in propylene polymerization mediated by an isospecific metallocene catalyst (i.e., rac -dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride, I) activated with methylaluminoxane (MAO), rendering a catalytic access to styryl-capped isotactic polypropylenes (i -PP). The chain transfer reaction took place in a unique way where prior to the ultimate chain transfer DVB/H2 or BVPE/H2 caused a copolymerization-like reaction leading to the formation of main chain benzene rings. A preemptive polymer chain reinsertion was deduced after the consecutive actions of DVB/H2 or BVPE/H2, which gave the styryl-terminated polymer chain alongside a metal-hydride active species. It was confirmed that the chain reinsertion occurred in a regio-irregular 1,2-fashion, which contrasted with a normal 2,1-insertion of styrene monomer and ensured subsequent continuous propylene insertions, directing the polymerization to repeated DVB or BVPE incorporations inside polymer chain. Only as a competitive reaction, the insertion of propylene into metal-hydride site broke the chain propagation resumption process while completed the chain transfer process by releasing the styryl-terminated polymer chain. BVPE was found with much higher chain transfer efficiency than DVB, which was attributed to its non-conjugated structure with much divided styrene moieties resulting in higher polymerization reactivity but lower chain reinsertion tendency. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3709,3713, 2010 [source]

Crosslinking polymerization leading to interpenetrating polymer network formation.


Abstract At the start of our research program concerned with the elucidation of the crosslinking polymerization mechanism leading to interpenetrating polymer network (IPN) formation, in which IPNs consist of both polymethacrylates and polyurethane (PU) networks, this article deals with the polyaddition crosslinking reaction leading to PU network formation. Therefore, 2-methacryloyloxyethyl isocyanate (MOI) was radically copolymerized with methyl methacrylate (MMA) in the presence of CBr4 as a chain-transfer agent. The resulting poly(MMA- co -MOI)s, having pendant isocyanate (NCO) groups as novel multifunctional polyisocyanates, were used for polyaddition crosslinking reactions with ethylene glycol as a typical diol. The second-order rate constants depended on both the functionality of poly(MMA- co -MOI) and the NCO group concentration. The actual gel points were compared with the theoretical ones calculated according to Macosko's equation; the deviation of the actual gel point from the theoretical value became more remarkable for a greater functionality of poly(MMA- co -MOI) and at a lower NCO group concentration or at a lower poly(MMA- co -MOI) concentration. These are discussed mechanistically, with consideration given to the significance of intramolecular cyclization and intramolecular crosslinking reactions leading to the shrinkage of the molecular size of the prepolymer, along with the data of the intrinsic viscosities of resulting prepolymers and the swelling ratios of resulting gels. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 606,615, 2003 [source]

Study of fragmentation pathways of lithiated ,,, -unsaturated thioesters by electrospray ionization mass spectrometry

Cheng Guo
The fragmentation pathways of lithiated ,,, -unsaturated thioesters with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in positive ion mode. In mass spectrometry of the ,,, -unsaturated thioesters, Ar-CHCH-CO-S-Ph, loss of PhSLi and elimination of a thiophenol were the two major fragmentation reactions of the lithiated molecules. The elemental compositions of all the ions were confirmed by high-resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MS/MS). The thioesters studied here were para -monosubstituted on the phenyl ring of cinnamoyl and the electron-withdrawing groups favored loss of a thiophenol, whereas the electron-releasing groups strongly favored the competing reaction leading to the loss of PhSLi to form a cinnamoyl cation, Ar-CHCHCO+. The intensity ratios of the two competitive product ions were well correlated with the , substituent constants. The mechanisms of these two competing routes were further investigated by density functional theory (DFT) calculations. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Gas-phase ion chemistry of Glu/Met systems,

H. Wincel
A combined chemical ionisation and tandem mass spectrometry (MS/MS) approach has been used for investigation of the gas-phase ion chemistry of systems containing the amino acids Glu and Met, and the dipeptides ,-Glu-Met and Met-Glu. The metastable fragmentation of the protonated dimer, (Glu)2H+, reveals an intracluster reaction leading to the elimination of the Glu residue. The main features of the ion-molecule reactions observed in the systems containing Glu and Glu,+,Met can be described in terms of sequential adduct formation. The results obtained for the thermal dehydration of Glu were used to rationalise the formation of the proton-bound structures (Glu,,,H2O)···H+··· (Glu,,,H2O) and (Glu,,,H2O)3·H+. The adduct ions, [(Glu,,,H2O),+,H,+,Glu]+ and [(Glu,,,H2O),+ H,+,Met]+, and further association products were also observed. The results lead to a reconsideration of the structural aspects proposed earlier for these species in the sense that they suggest that the systems correspond to a mixture of isomeric covalent and proton-bound structures. The thermal effects on the decomposition of the neutral (,-Glu-Met) and its protonated form, (,-Glu-Met)H+, at m/z 279 were investigated, and dramatic changes in the MI spectra of the m/z 279 ion with temperature were found. A mechanistic explanation for the observed evolution of higher mass ion peaks in the mass spectra is developed. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Antigenic as Well as Nonantigenic Stimuli Induce Similar Middle Ear Responses in the Rat,

Edith L. G. M. Tonnaer MSc
Abstract Objectives/Hypothesis The observation that during otitis media many different types of micro-organisms have been cultured from effusions indicate that, once present in the middle ear cavity, most types of micro-organisms are able to trigger an inflammatory reaction leading to otitis media. The present study was designed to determine the middle ear response after injection of different substances into the middle ear cavity. Study Design To determine whether and to what extent an inflammatory response of the middle ear depends on the entering agent, the response in the tympanic cavity was studied by otomicroscopy and histological examination after inoculation of various substances. Methods Lewis rats were inoculated in transtympanic fashion either with live or heat-killed bacteria (pathogenic and nonpathogenic), Keyhole limpet hemocyanin, active charcoal, or saline. The mucosal response of the challenged middle ears was studied histologically. Results Irrespective of the inoculated substance, no essential differences in the mucosal response were found. The intensity of the inflammatory response was greater when live bacteria were inoculated. Conclusions The present study demonstrates that any substance reaching the middle ear cavity is likely to induce otitis media. These observations emphasize the role of the eustachian tube as "porte d'entrée" in the pathogenesis of this disorder. Determination of specific aspects of the eustachian tube involved in protection or in facilitating bacterial translocation will be important for the understanding of the pathogenesis of otitis media and the subsequent development of new therapeutic strategies. In addition, elucidation of bacterial factors involved in the process of colonization and translocation will be of equal importance. [source]

Oxidized nitrogen and ozone interaction with forests.

I: Experimental observations, analysis of exchange with Douglas fir
Abstract Measurements of NOx and O3 exchange to and from a forest canopy are described with reference to canopy and ecosystem processes leading to emission of NO2. The soil below the forested measurement location is shown to be a net source of reactive oxidized nitrogen (as NO). It is shown that a large fraction (around 58% on average) of the emitted NO escapes out of the trunk space to react within and above the canopy. Fluxes of NO2 above the canopy are bi-directional, with large fluxes and most emission events taking place during the day. Deposition is shown to take place without significant changes in the vertical flux; however there appears to be rapid chemical reaction leading to significant flux divergence taking place during emission events. Above the top of the canopy (22 m), changes of 200% in the NO2 flux between 25 and 35 m are not uncommon. Ozone deposition to the forest system has been investigated. The flux is often related to stomatal deposition, but there are periods when large non-stomatal fluxes are observed. At night there is a large vertical divergence in the ozone flux above the canopy, probably related to reaction with NO from the forest soil. The reaction of O3 with volatile organic compounds is found, in general, to be negligible with respect to ozone concentrations and fluxes. Ozone is found to deposit mainly to leaf stomata during the day, with a small but not insignificant contribution from NO reaction. However, the nocturnal ozone budget for the forest changes significantly, with most of the measured deposition accounted for by soil uptake and reaction with NO. The resultant problems related to inadequate treatment of air chemistry when interpreting O3 fluxes in high NO emission environments are identified. Copyright © 2004 Royal Meteorological Society. [source]

Addition of Me3SiCN to trifluoromethyl derivates of N -(pyridylmethylidene) anilines catalyzed by Lewis acids

Irina Iovel
Abstract A series of novel Shiff bases (1a,h) was synthesized by condensation of pyridinecarboxaldehydes (1,4) with 3- and 4-trifluoromethylanilines (5, 6) in the presence of molecular sieves (4 Å). It was found that AlCl3 and AlBr3 catalyzed the addition of Me3SiCN to the CN bond of the imines obtained, whereas the other Lewis acids studied (YCl3, LaCl3, ZnI2) were not active. The reactivity of the imines in the title reaction, on the whole, correlated with their basicity. Besides the addition giving the expected ,-amino nitriles (2a,b,d,f,h), an unusual reaction leading to unsaturated nitriles (3a,h) was observed. The structures of saturated and unsaturated products 2d and 3c were determined by X-ray diffraction. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Intramolecular Reactions in Pseudo-Geminally Substituted [2.2]Paracyclophanes,

Lidija Bondarenko Dr.
Abstract A selection of pseudo-geminally substituted [2.2]paracyclophanes, the alkynes 6, 7, 10, 11,a, and 11,b and the alkenes 8 and 9 were prepared for the study of intraannular reactions between functional groups in direct juxtaposition. Whereas 9 and 10 provide the corresponding cyclobutane and cyclobutene derivatives on irradiation (12 and 13, respectively), the bis-alkynes 7 and 11,b do not lead to a cyclobutadiene intermediate. In the latter case the "half-closed" butadiene derivative 17 was isolated. A Paterno,Büchi reaction took place on irradiation of 8 and 6, although the oxetene intermediate 21 produced in the second example did not survive the reaction conditions (ring-opening to 22). Bromine addition to 9, 10, and 7 occurred with high stereoselectivity (formation of the dibromides 27, 30, and 33, respectively), and is rationalized by postulating the formation of the cationic intermediates 26, 29, and 32, respectively. To study the interaction of a carbocation with a facing triple bond, the alcohol 34 was prepared from 6. On acid treatment ring closure to the triply-bridged phane 38 took place, accompanied by the hydration of the triple bond to the ketoalcohol 37. In an interesting intraannular [2+3]cycloaddition reaction the bis-acetylene 11,a, on treatment with n -butyl lithium, provided the cyclopentadiene derivative 42. That the two triple bonds of a pseudo-geminal diacetylene can engage in a cyclization reaction leading to the cyclopentadienone complex 44 was also shown by treating 11,b with iron pentacarbonyl. [source]

Efficient Preparation of Photoswitchable Dithienylethene-Linker-Conjugates by Palladium-Catalyzed Coupling Reactions of Terminal Alkynes with Thienyl Chlorides and Other Aryl Halides

Marc Zastrow
Abstract Three photochromic dithienylethene-linker-conjugates with an adamantane core containing different spacer lengths and footprint areas with carboxylic anchoring groups are synthesized. The synthetic routes start either from the ethynylene-linker 5 or the iodo-substituted linker 8. Reaction conditions for the final Sonogashira coupling step between ethynylene-linker 5 with the chloro-substituted dithienylethene 4 in the presence of [PdCl2(CH3CN)2]/X-Phos and Cs2CO3 or K3PO4 are optimized using 2-chloro-5-methylthiophene (9) and triethylsilylacetylene or triisopropylsilylacetylene (10,a,b) as model compounds. Experimental conditions are found to suppress the activation of the C(sp)Si bond in TIPS-acetylene 10,b, a reaction leading to a subsequent cross-coupling reaction to form by-product 12. Furthermore, activation of the C(sp)Si bond in the presence of the fluorinated backbone of the chloro-substituted dithienylethene 4 can also be prevented. The photochromic properties of the conjugate 3 and its precursor dithienylethene 7,b are also investigated. Beschrieben wird die Synthese von drei photochromen Dithienylethen-Linker-Konjugaten, bestehend aus einer zentralen Adamantaneinheit, Carbonsäure-Ankergruppen, sowie variierenden "Spacerlängen" und unterschiedlichen Fußabdrücken. Die synthetischen Routen zu diesen Verbindungen beginnen entweder ausgehend von dem Ethinylen-Linker 5 oder von dem Iod-substituierten Linker 8. Für die finale Sonogashira-Kupplung wurden dabei Reaktionsbedingungen zwischen dem Ethinylen-Linker 5 und dem Chlor-substituierten Dithienylethen 4 in Gegenwart von [PdCl2(CH3CN)2]/X-Phos und Cs2CO3 oder K3PO4 verwendet, die anhand von Modellstudien mit 2-Chlor-5-methylthiophen (9) und Triethylsilylacetylen oder Triisopropylsilylacetylen (10,a,b) optimiert wurden. Dabei wurden experimentelle Bedingungen gefunden, um die Aktivierung der C(sp)-Si-Bindung von TIPS-Acetylen 10,b zu unterdrücken, welche ansonsten zu dem Nebenprodukt 12 führte. Darüber hinaus konnte die Aktivierung der C(sp)-Si-Bindung in Anwesenheit des fluorierten Rückgrats des chlor-substituierten Dithienylethen 4 verhindert werden. Schließlich wurden die photochromen Eigenschaften des Konjugates 3 und der Vorläuferverbindung 7,b untersucht. [source]

Fatal infant nasal seawater spray instillation

Milivoj Novak
Abstract The use of seawater nasal spray is considered safe and sold as a non-prescription medicine. However, it is well known that nasal manipulations can provoke vagal reaction leading to acute life-threatening events. A case of fatal seawater nasal spray application in an infant is presented. Conclusion: We do not consider the use of seawater nasal spray to be absolutely safe, especially among infants with disordered autonomic function. [source]