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Rearrangement Reactions (rearrangement + reaction)
Selected AbstractsChemInform Abstract: Unexpected Novel Rearrangement Reaction: Synthesis of Benzo-Medium-Ring Anhydride.CHEMINFORM, Issue 38 2008Wen-Liang Dong 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: Epoxide Ring-Opening and Meinwald Rearrangement Reactions of Epoxides Catalyzed by Mesoporous Aluminosilicates.CHEMINFORM, Issue 45 2009Mathew W. C. Robinson 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: 3-Pyrrolidinones: Michael Addition and Schmidt Rearrangement Reactions.CHEMINFORM, Issue 26 2009F. A. Amer 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: Rearrangement Reactions.CHEMINFORM, Issue 47 2008Part 15. 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: Highly Regioselective Decarboxylative Claisen Rearrangement Reactions of Diallyl 2-Sulfonylmalonates.CHEMINFORM, Issue 7 2008Donald Craig 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] Regioselective [5,5]-Sigmatropic Rearrangement Reactions of Aryl Hydrazides.CHEMINFORM, Issue 37 2006Hong-Min Kang 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, please click on HTML or PDF. [source] Interesting Acid-Catalyzed O,N-Type Smiles Rearrangement Reactions of 2-Pyrimidinyloxy-N-arylbenzylamine Derivatives.CHEMINFORM, Issue 41 2005Hao-Yang Wang Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Intramolecular Radical Rearrangement Reactions of 2-Methyleneaziridines: Application to the Synthesis of Substituted Piperidines, Decahydroquinolines, and Octahydroindolizines.CHEMINFORM, Issue 46 2001Natacha Prevost Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] Platinum- and Gold-Catalyzed Rearrangement Reactions of Propargyl Acetates: Total Syntheses of (,)-,-Cubebene, (,)-Cubebol, Sesquicarene and Related TerpenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2006Alois Fürstner Prof. Abstract Propargyl acetates, in the presence of catalytic amounts of late transition-metal salts such as PtCl2 or AuCl3, represent synthetic equivalents of ,-diazoketones. This notion is corroborated by a concise approach to various sesquiterpene natural products starting from readily available substrates. Specifically, (+)-carvomenthone (17) is converted into propargyl acetate (S)- 26 by a sequence involving Stille cross-coupling of its kinetic enol triflate 18, regioselective hydroboration/oxidation of the resulting 1,3-diene 19, and addition of an alkynyl cerium reagent to aldehyde 21 thus obtained. Since the latter step was found to be unselective, the configuration of the reacting propargyl acetate was unambiguously set by oxidation followed by diastereoselective transfer hydrogenation by using Noyori's catalyst 25. Compound (S)- 26, on treatment with PtCl2 in toluene, converted exclusively to the tricyclic enol acetate 27, which was saponified to give norcubebone 11 in excellent overall yield. The conversion of this compound into the sesquiterpene alcohol (,)-cubebol (6) was best achieved with MeCeCl2 as the nucleophile, whereas the formation of the parent hydrocarbon (,)-,-cubebene (4) was effected in excellent yield by recourse to iron-catalyzed cross coupling methodology developed in this laboratory. Since norketone 11 has previously been transformed into (,)-,-cubebene (5) as well as (,)-4-epicubebol 8, our approach constitutes formal total syntheses of these additional natural products as well. Along similar lines, the readily available propargyl acetates 1, 33 and 47 were shown to give access to 2-carene 44, sesquicarene 39, and episesquicarene 51 in excellent overall yields. In this series, however, the cycloisomerization reaction was best achieved with catalytic amounts of AuCl3 in 1,2-dichloroethane as the solvent. In addition to these preparative results, our data provide some insight into the mechanism of these remarkable skeletal rearrangement reactions. Transformations of this type are likely triggered by initial coordination of the alkyne unit of the substrate to the carbophilic transition-metal cation. Formal attack of the alkene moiety onto the resulting ,-complex engenders the formation of an electrophilic cyclopropyl carbene species which subsequently reacts with the adjacent acetate unit to give the final product. The alternative phasing of events, implying initial attack of the acetate (rather than the alkene moiety) onto the metal,alkyne complex, is inconsistent with the stereochemical data obtained during this total synthesis campaign. [source] Studies of the Interesting Gas-phase Rearrangement Reactions of 2-Pyrimidinyloxy- N -arylbenzylurea Promoted by Urea-Carbamimidic Acid Tautomerism by ESI-MS/MS and Theoretical Computation,CHINESE JOURNAL OF CHEMISTRY, Issue 9 2010Chu Xu Abstract The gas-phase rearrangement reactions of compound 1, 2-dimethoxypyrimidinyloxybenzylaminoben- zenedipropylurea, were studied by ESI-MS/MS. The experimental results showed that introduction of dipropylurea moiety into the molecule initiated various interesting gas-phase chemistries and the mechanisms were proposed on the basis of hydrogen/deuterium (H/D) exchange experiments and theoretical computations. Moreover, product 2, the solution-phase rearrangement product of compound 1, was synthesized and its gas-phase chemistries were also studied to support the propos gas-phase rearrangement reactions of compound 1. [source] Tandem Carbon,Carbon Bond Constructions via Catalyzed Cyanation/Brook Rearrangement/C-Acylation Reactions of Acylsilanes.CHEMINFORM, Issue 51 2002Xin Linghu No abstract is available for this article. [source] Berichtigung: Asymmetric Tandem Wittig Rearrangement/Mannich ReactionsANGEWANDTE CHEMIE, Issue 24 2010Natalie No abstract is available for this article. [source] Asymmetric Tandem Wittig Rearrangement/Mannich Reactions,ANGEWANDTE CHEMIE, Issue 16 2010Natalie Man hat die Wahl: Eine hoch stereoselektive Synthese von ,-Alkyl-,-hydroxy-,-aminoestern gelingt in einer Tandemreaktionssequenz aus Wittig-Umlagerung und Mannich-Reaktion. N -Benzyl- und N -Boc-Imine werden mit hoher Selektivität in die syn -Aminoalkohole überführt (siehe Beispiel), während N -Boc-2-(phenylsulfonyl)amine anti -Aminoalkohole liefern. Nach Abspaltung des Auxiliars (Umesterung oder Reduktion) werden die Produkte mit bis zu 96,%,ee erhalten. [source] Atmospheric chemistry of isopropyl formate and tert -butyl formateINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2010Andre Silva Pimentel Formates are produced in the atmosphere as a result of the oxidation of a number of species, notably dialkyl ethers and vinyl ethers. This work describes experiments to define the oxidation mechanisms of isopropyl formate, HC(O)OCH(CH3)2, and tert -butyl formate, HC(O)OC(CH3)3. Product distributions are reported from both Cl- and OH-initiated oxidation, and reaction mechanisms are proposed to account for the observed products. The proposed mechanisms include examples of the ,-ester rearrangement reaction, novel isomerization pathways, and chemically activated intermediates. The atmospheric oxidation of isopropyl formate by OH radicals gives the following products (molar yields): acetic formic anhydride (43%), acetone (43%), and HCOOH (15,20%). The OH radical initiated oxidation of tert -butyl formate gives acetone, formaldehyde, and CO2 as major products. IR absorption cross sections were derived for two acylperoxy nitrates derived from the title compounds. Rate coefficients are derived for the kinetics of the reactions of isopropyl formate with OH (2.4 ± 0.6) × 10,12, and with Cl (1.75 ± 0.35) × 10,11, and for tert -butyl formate with Cl (1.45 ± 0.30) × 10,11 cm3 molecule,1 s,1. Simple group additivity rules fail to explain the observed distribution of sites of H-atom abstraction for simple formates. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 479,498, 2010 [source] Ligand-Accelerated Asymmetric [1,2]-Stevens Rearrangment of Sulfur Ylides via Decomposition of Diazomalonates Catalyzed by Chiral Bisoxazoline/Copper ComplexADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Jian-Ping Qu Abstract The first example of catalytic asymmetric [1,2]-Stevens rearrangement reaction of 1,3-oxathiolanes with diazomalonates has been developed and up to 90% ee is achieved by the bisoxazoline 4e/copper(II) triflate [Cu(OTf)2] complex. [source] Novel benzyl rearrangements in electrospray ionization multistage tandem mass spectra of benzyl 2,,3, - didehydro-2,,3, -dideoxythymidin-5, -yl H-phosphonateJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2004Yi Chen Abstract Several alkyl 2,,3, -didehydro-2,,3, -dideoxythymidin-5, -yl H-phosphonates were synthesized and analyzed by electrospray ionization multistage tandem mass spectrometry (ESI , MSn). Two kinds of novel benzyl rearrangement reactions were observed in ESI , MS2 of [M + H]+, [M + Na]+ and [M + K]+ of benzyl 2,,3, -didehydro-2,,3, -dideoxythymidin-5, -yl H-phosphonate. Results from tandem mass spectrometry, high-resolution mass spectrometry and control experiments showed that the benzyl migration could undergo a four-membered cyclic rearrangement reaction, and benzyl was essential in the process. Copyright © 2004 John Wiley & Sons, Ltd. [source] Rearrangement process occurring in the fragmentation of adefovir derivativesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2004Xiaoyan Chen Abstract The fragmentation of the antiviral drug adefovir dipivoxil and its two active metabolites, adefovir and monopivoxil adefovir, was investigated using both ion trap and triple-quadrupole mass spectrometers. Fragment ions due to loss of 30 Da were observed and attributed to an unanticipated rearrangement process by loss of formaldehyde. The proposed mechanism is supported with the aid of three newly synthesized adefovir derivatives and with accurate mass measurement. Other fragmentations by loss of a pivaloyl group, loss of water, C,P bond cleavage and C,O bond cleavage were also observed for adefovir derivatives. It was concluded that the compounds containing a >POO,CHR,OCO, group generally displayed a rearrangement reaction by loss of RCHO in collision-induced dissociation, and the process generally required an activation energy lower than for a direct bond cleavage. Copyright © 2004 John Wiley & Sons, Ltd. [source] Computational studies on the reactions of 3-butenyl and 3-butenylperoxy radicalsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2010Akira MiyoshiArticle first published online: 11 MAR 2010 The reactions of 3-butenyl (,CH2CH2CHCH2) radicals,unimolecular decomposition, isomerization, as well as reaction with O2,and the subsequent unimolecular rearrangement reactions of the 3-butenylperoxy radicals have been investigated and are compared to the analogous reactions of butyl (,CH2CH2CH2CH3) and butylperoxy radicals using transition-state theory based on the quantum chemical calculations at the CBS-QB3 level. For alkyl-analogue processes, the reactions of 3-butenyl and 3-butenylperoxy radicals can be well characterized by the decreased and increased bond dissociation energies at the allylic and vinylic sites, respectively. The intramolecular addition reactions of the radical center atoms to the double bonds were found to be important non-alkyl-analogue reactions of 3-butenyl and 3-butenylperoxy radicals. As a consequence, the thermal decomposition of 3-butenyl radicals was found to be slower than that of butyl radicals by one order of magnitude at temperature near 1000 K. Intramolecular addition reactions are suggested to be the predominant unimolecular rearrangement processes of 3-butenylperoxy radicals over the entire temperature range investigated (500,1200 K). The intramolecular addition reactions of the alkenyl peroxy radicals, which have not been included in combustion kinetic models, and their implications for the autoignition of alkenes are discussed. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 273,288, 2010 [source] Novel benzyl rearrangements in electrospray ionization multistage tandem mass spectra of benzyl 2,,3, - didehydro-2,,3, -dideoxythymidin-5, -yl H-phosphonateJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2004Yi Chen Abstract Several alkyl 2,,3, -didehydro-2,,3, -dideoxythymidin-5, -yl H-phosphonates were synthesized and analyzed by electrospray ionization multistage tandem mass spectrometry (ESI , MSn). Two kinds of novel benzyl rearrangement reactions were observed in ESI , MS2 of [M + H]+, [M + Na]+ and [M + K]+ of benzyl 2,,3, -didehydro-2,,3, -dideoxythymidin-5, -yl H-phosphonate. Results from tandem mass spectrometry, high-resolution mass spectrometry and control experiments showed that the benzyl migration could undergo a four-membered cyclic rearrangement reaction, and benzyl was essential in the process. Copyright © 2004 John Wiley & Sons, Ltd. [source] Negative ion electrospray ionization mass spectrometry of nucleoside phosphoramidate monoesters: elucidation of novel rearrangement mechanisms by multistage mass spectrometry incorporating in-source deuterium labellingRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2008Peng-Xiang Xu Several O-2,,3,-isopropylideneuridine-O-5,-phosphoramidate monoesters were synthesized and analyzed by negative ion electrospray ionization tandem mass spectrometry (ESI-MSn). Two kinds of novel rearrangement reactions were observed due to the difference in the amino acid in the nucleoside phosphoramidate monoesters, and possible mechanisms were proposed. One involves a five-membered cyclic transition state. The other is formation of a stable five-membered ring intermediate by Michael addition. Results were confirmed by tandem mass spectrometry and isotopically labeled hydrogen atoms. Furthermore, the internal hydrogen exchange between active hydrogen and methyl acrylate in the heated capillary of the mass spectrometer was found. The characteristic fragmentation behavior in ESI-MS may be used to monitor this kind of compounds in the biological metabolism. Copyright © 2008 John Wiley & Sons, Ltd. [source] Adenosyl Radical: Reagent and Catalyst in Enzyme ReactionsCHEMBIOCHEM, Issue 5 2010E. Neil G. Marsh Prof. Abstract Adenosine is undoubtedly an ancient biological molecule that is a component of many enzyme cofactors: ATP, FADH, NAD(P)H, and coenzyme A, to name but a few, and, of course, of RNA. Here we present an overview of the role of adenosine in its most reactive form: as an organic radical formed either by homolytic cleavage of adenosylcobalamin (coenzyme B12, AdoCbl) or by single-electron reduction of S -adenosylmethionine (AdoMet) complexed to an iron,sulfur cluster. Although many of the enzymes we discuss are newly discovered, adenosine's role as a radical cofactor most likely arose very early in evolution, before the advent of photosynthesis and the production of molecular oxygen, which rapidly inactivates many radical enzymes. AdoCbl-dependent enzymes appear to be confined to a rather narrow repertoire of rearrangement reactions involving 1,2-hydrogen atom migrations; nevertheless, mechanistic insights gained from studying these enzymes have proved extremely valuable in understanding how enzymes generate and control highly reactive free radical intermediates. In contrast, there has been a recent explosion in the number of radical-AdoMet enzymes discovered that catalyze a remarkably wide range of chemically challenging reactions; here there is much still to learn about their mechanisms. Although all the radical-AdoMet enzymes so far characterized come from anaerobically growing microbes and are very oxygen sensitive, there is tantalizing evidence that some of these enzymes might be active in aerobic organisms including humans. [source] Platinum- and Gold-Catalyzed Rearrangement Reactions of Propargyl Acetates: Total Syntheses of (,)-,-Cubebene, (,)-Cubebol, Sesquicarene and Related TerpenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2006Alois Fürstner Prof. Abstract Propargyl acetates, in the presence of catalytic amounts of late transition-metal salts such as PtCl2 or AuCl3, represent synthetic equivalents of ,-diazoketones. This notion is corroborated by a concise approach to various sesquiterpene natural products starting from readily available substrates. Specifically, (+)-carvomenthone (17) is converted into propargyl acetate (S)- 26 by a sequence involving Stille cross-coupling of its kinetic enol triflate 18, regioselective hydroboration/oxidation of the resulting 1,3-diene 19, and addition of an alkynyl cerium reagent to aldehyde 21 thus obtained. Since the latter step was found to be unselective, the configuration of the reacting propargyl acetate was unambiguously set by oxidation followed by diastereoselective transfer hydrogenation by using Noyori's catalyst 25. Compound (S)- 26, on treatment with PtCl2 in toluene, converted exclusively to the tricyclic enol acetate 27, which was saponified to give norcubebone 11 in excellent overall yield. The conversion of this compound into the sesquiterpene alcohol (,)-cubebol (6) was best achieved with MeCeCl2 as the nucleophile, whereas the formation of the parent hydrocarbon (,)-,-cubebene (4) was effected in excellent yield by recourse to iron-catalyzed cross coupling methodology developed in this laboratory. Since norketone 11 has previously been transformed into (,)-,-cubebene (5) as well as (,)-4-epicubebol 8, our approach constitutes formal total syntheses of these additional natural products as well. Along similar lines, the readily available propargyl acetates 1, 33 and 47 were shown to give access to 2-carene 44, sesquicarene 39, and episesquicarene 51 in excellent overall yields. In this series, however, the cycloisomerization reaction was best achieved with catalytic amounts of AuCl3 in 1,2-dichloroethane as the solvent. In addition to these preparative results, our data provide some insight into the mechanism of these remarkable skeletal rearrangement reactions. Transformations of this type are likely triggered by initial coordination of the alkyne unit of the substrate to the carbophilic transition-metal cation. Formal attack of the alkene moiety onto the resulting ,-complex engenders the formation of an electrophilic cyclopropyl carbene species which subsequently reacts with the adjacent acetate unit to give the final product. The alternative phasing of events, implying initial attack of the acetate (rather than the alkene moiety) onto the metal,alkyne complex, is inconsistent with the stereochemical data obtained during this total synthesis campaign. [source] Studies of the Interesting Gas-phase Rearrangement Reactions of 2-Pyrimidinyloxy- N -arylbenzylurea Promoted by Urea-Carbamimidic Acid Tautomerism by ESI-MS/MS and Theoretical Computation,CHINESE JOURNAL OF CHEMISTRY, Issue 9 2010Chu Xu Abstract The gas-phase rearrangement reactions of compound 1, 2-dimethoxypyrimidinyloxybenzylaminoben- zenedipropylurea, were studied by ESI-MS/MS. The experimental results showed that introduction of dipropylurea moiety into the molecule initiated various interesting gas-phase chemistries and the mechanisms were proposed on the basis of hydrogen/deuterium (H/D) exchange experiments and theoretical computations. Moreover, product 2, the solution-phase rearrangement product of compound 1, was synthesized and its gas-phase chemistries were also studied to support the propos gas-phase rearrangement reactions of compound 1. [source] | |||||||||||||||||||||||||