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Curt Wentrup - One of the best experts on this subject based on the ideXlab platform.
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cumulene rearrangements Ketene Ketene isocyanate isocyanate thioKetene Ketene imidoylKetene ketenimine and Ketene allene rearrangements
Current Organic Chemistry, 2010Co-Authors: Curt Wentrup, Justin J Finnerty, Rainer KochAbstract:Interconversions between alpha-oxoKetenes, imidoylKetenes and alpha-oxoketenimines, thioacylKetenes and acylthioKetenes, vinylKetenes and acylallenes, isocyanates, and thioacylisocyanates and acylisothiocyanates take place by means of 1,3-shifts of substituents, which are facilitated by electron-rich migrating groups, especially those containing lone pairs on the migrating atoms. A bonding interaction between the lone pair orbital and the LUMO of the cumulene moiety stabilizes the transition state and can even make it become an intermediate. The 1,3-shifts can also be said to be pseudopericyclic reactions. The 1,3-migration of aryl groups is accelerated by electron-donating substituents in the phenyl ring. In general, for like substituents, migratory aptitudes decrease in the series alpha-oxoKetene > imidoylKetenes > acylallene > vinylKetene.
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2‐Cyano(2‐pyridyl)Ketene
European Journal of Organic Chemistry, 2002Co-Authors: Carsten Plüg, Arvid Kuhn, Curt WentrupAbstract:Flash vacuum thermolysis of quinolizinones is a new way of generating Ketenes. The title Ketene is obtained from 1-cyano-2-hydroxyquinolizine-4-one and characterized by its Ar matrix infrared spectrum. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany 2002.
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Reactivity of Ketenes in Matrices. Direct Observation of Ketene−Pyridine Ylides
Journal of the American Chemical Society, 1996Co-Authors: Greg G. Qiao, John Andraos, Curt WentrupAbstract:Ketenes 7, 14, and 17 have been generated in pyridine matrices and observed by infrared spectroscopy to react with pyridine at temperatures between 15 and 50 K to form Ketene−pyridine ylides 12, 15, and 18. Azaheterocyclic Ketenes 20, 23, and 26 dimerize or tetramerize at ca. 50 K, whereby one Ketene molecule acts as a nucleophile toward the other, forming a transient Ketene−imine ylide.
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(Cyanovinyl)Ketenes from azafulvenones. An apparent retro-Wolff rearrangement
Journal of the American Chemical Society, 1996Co-Authors: Greg G. Qiao, Wim Meutermans, Ming Wah Wong, Michael Träubel, Curt WentrupAbstract:Flash vacuum pyrolyses or pulsed pyrolysis of azole esters 1b and 20 and their carboxylic acids 1a and 19 or acid chloride 1c give five-membered ring Ketenes (azafulvenones) 2 and 24 which dimerize to diketopiperazines 3 and 21 but also undergo efficient rearrangement to (cyanovinyl)- and (o-cyanophenyl)Ketene (6 and 27). The same products are obtained by elimination of alcohol from esters of these (cyanovinyl)Ketenes. Both types of Ketenes are observed directly by IR spectroscopy and are trapped by alcohols to give the corresponding azole esters or (cyanovinyl)acetates. 1-Carbonyl-1H-isoindole (34) is a highly reactive Ketene, dimerizing at 50 K. All Ketene IR spectra are in good accord with ab initio calculations. The mechanism of this apparent retro-Wolff rearrangement is discussed.
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Ketene-Ketene Rearrangement: Substituent Effects on the 1,3-Migration in .alpha.-Oxo Ketenes
The Journal of Organic Chemistry, 1994Co-Authors: Ming Wah Wong, Curt WentrupAbstract:The mechanism of the 1,3 migration in a series of a-ore Ketenes, RCOCH=C=O (R = H, CH3, NH2, OH, SH, SiH3, OCH3, SCH3, N(CH3)(2), and C6H5),was studied by high-level ab initio molecular orbital calculations up to the QCISD(T)/6-311+G(2d,p) + ZPVE level of theory, The ore Ketene-oxo Ketene rearrangement is predicted to proceed via a four-membered cyclic transition structure. The calculated activation barrier depends strongly on the nature of the migrating group (R), ranging from 20 to 200 kJ mol(-1). n-Electron donor substituents (e.g., NH2 and SH) are found to stabilize the four-centered transition structures. For the dimethylamino substituent, the 1,3-shift is predicted to be a facile process (barrier = 20 kJ mol(-1)), and a stable four-membered cyclic interemediate is found to exist on the reaction profile. The predicted 1,3-migratory aptitude is in the order N(CH3)(2) > SCH3 > SH > NH2 > OCH3 > OH > SiH3 > H > C6H5 > CH3. This calculated trend is consistent with experimental observations. The stabilization of the transition structure can be rationalized by the donor-acceptor interaction between an appropriate n- or pi-electron donor substituent and the vacant carbon p orbital of the Ketene LUMO. The E/Z conformational preferences (gas phase and solution), rotational barriers, and IR spectra of alpha-ore Ketenes are also reported.
Jacqueline Collin - One of the best experts on this subject based on the ideXlab platform.
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Tandem reactions catalyzed by lanthanide iodides. Part 1: Tandem Mukaiyama–Michael iminoaldol reactions
Tetrahedron, 2004Co-Authors: Nada Jaber, Martine Assié, Jean-claude Fiaud, Jacqueline CollinAbstract:Abstract Samarium diiodide, as well as lanthanide triiodides catalyze a one-pot procedure allowing to perform sequentially the Mukaiyama–Michael addition of a Ketene silyl acetal on a cyclic α,β-unsaturated ketone, followed by the addition of a glyoxylic, aromatic or heteroaromatic imine. According to the nature of the silyl group the adducts resulting from this tandem process are isolated as ketones or as enoxysilanes. The presence of a coordinating group on the imine increases the rate of the reaction.
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Tandem Michael imino–aldol reactions catalyzed by samarium diiodide
Tetrahedron Letters, 2001Co-Authors: Nada Jaber, Jean-claude Fiaud, Jacqueline CollinAbstract:Abstract Samarium diiodide catalyzes a one-pot procedure allowing to perform sequentially the Michael addition of a Ketene silyl acetal on a cyclic α,β-unsaturated ketone, followed by the addition of a glyoxylic or aromatic imine. The presence of a coordinating group on the imine increases the rate of the reaction.
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Tandem Mukaiyama Michael-aldol reactions catalyzed by samarium diiodide
Tetrahedron Letters, 1998Co-Authors: Nicolas Giuseppone, Yann Courtaux, Jacqueline CollinAbstract:Abstract Samarium diiodide catalyzes a one pot procedure allowing to perform sequentially the Mukaiyama-Michael addition of a Ketene silyl acetal on a cyclic α,β-unsaturated ketone, followed by a Mukaiyama aldol reaction of an aldehyde. The adducts are isolated as silyl ethers in good yields and in most cases with high diastereoselectivity.
Chunmei Zhang - One of the best experts on this subject based on the ideXlab platform.
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reactivity of lanthanocene amide complexes toward Ketenes unprecedented organolanthanide induced conjugate electrophilic addition of Ketenes to arenes
Chemistry: A European Journal, 2006Co-Authors: Chunmei Zhang, Xigeng Zhou, Linhong WengAbstract:This paper presents some unusual types of reactions of lanthanocene amide complexes with Ketenes, and demonstrates that these reactions are dependent on the nature of amide ligands and Ketenes as well as the stoichiometric ratio under the conditions involved. The reaction of [{Cp2LnNiPr2}2] with four equivalents of Ph2CCO in toluene affords the unexpected enolization dearomatization products [Cp2Ln(OC{2,5-C6H5(CPhCONiPr2-4)}CPh2)] (Ln = Yb (1 a), Er (1 b)) in good yields, representing an unprecedented conjugate electrophilic addition to a non-coordinated benzenoid nucleus. Treatment of [{Cp2LnNiPr2}2] with four equivalents of PhEtCCO under the same conditions gives the unexpected enolization dearomatization/rearomatization products [{Cp2Ln(OC{C6H4(p-CHEtCONiPr2)}CEtPh)}2] (Ln = Yb (2 a), Er (2 b), Dy (2 c)). However, reaction of [{Cp2YbNiPr2}2] with PhEtCCO in THF forms only the mono-insertion product [Cp2Yb{OC(NiPr2)CEtPh}](THF) (3). Hydrolysis of 2 afforded aryl ketone PhEtCHCOC6H4(p-CHEtCONiPr2) (4) and the overall formation of aryl ketone 4 provides an alternative route to the acylation of aromatic compounds. Moreover, reaction of [{Cp2LnNHPh}2] with excess of PhEtCCO or Ph2CCO in toluene affords only the products from a formal insertion of the CC bond of the Ketene into the NH bond, [(Cp2Ln{OC(CHEtPh)NPh})2] (Ln = Yb (5 a), Y (5 b)) or [(Cp2Er{OC(CHPh2)NPh})2] (6), respectively, indicating that an isomerization involving a 1,3-hydrogen shift occurs more easily than the conjugate electrophilic addition reaction, along with the initial amide attack on the Ketene carbonyl carbon. [{Cp2ErNHEt}2] reacts with an excess of PhEtCCO to give [(Cp2Er{PhEtCHCON(Et)COCEtPh})2] (7), revealing another unique pattern of double-insertion of Ketenes into the metal–ligand bond without bond formation between two Ketene molecules. All complexes were characterized by elemental analysis and by their spectroscopic properties. The structures of complexes 1 b, 2 a, 2 b, 5 a, 5 b, 6, and 7 were also determined through X-ray single-crystal diffraction analysis.
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Reactivity of Lanthanocene Amide Complexes toward Ketenes: Unprecedented Organolanthanide‐Induced Conjugate Electrophilic Addition of Ketenes to Arenes
Chemistry: A European Journal, 2006Co-Authors: Chunmei Zhang, Xigeng Zhou, Lin‐hong WengAbstract:This paper presents some unusual types of reactions of lanthanocene amide complexes with Ketenes, and demonstrates that these reactions are dependent on the nature of amide ligands and Ketenes as well as the stoichiometric ratio under the conditions involved. The reaction of [{Cp2LnNiPr2}2] with four equivalents of Ph2CCO in toluene affords the unexpected enolization dearomatization products [Cp2Ln(OC{2,5-C6H5(CPhCONiPr2-4)}CPh2)] (Ln = Yb (1 a), Er (1 b)) in good yields, representing an unprecedented conjugate electrophilic addition to a non-coordinated benzenoid nucleus. Treatment of [{Cp2LnNiPr2}2] with four equivalents of PhEtCCO under the same conditions gives the unexpected enolization dearomatization/rearomatization products [{Cp2Ln(OC{C6H4(p-CHEtCONiPr2)}CEtPh)}2] (Ln = Yb (2 a), Er (2 b), Dy (2 c)). However, reaction of [{Cp2YbNiPr2}2] with PhEtCCO in THF forms only the mono-insertion product [Cp2Yb{OC(NiPr2)CEtPh}](THF) (3). Hydrolysis of 2 afforded aryl ketone PhEtCHCOC6H4(p-CHEtCONiPr2) (4) and the overall formation of aryl ketone 4 provides an alternative route to the acylation of aromatic compounds. Moreover, reaction of [{Cp2LnNHPh}2] with excess of PhEtCCO or Ph2CCO in toluene affords only the products from a formal insertion of the CC bond of the Ketene into the NH bond, [(Cp2Ln{OC(CHEtPh)NPh})2] (Ln = Yb (5 a), Y (5 b)) or [(Cp2Er{OC(CHPh2)NPh})2] (6), respectively, indicating that an isomerization involving a 1,3-hydrogen shift occurs more easily than the conjugate electrophilic addition reaction, along with the initial amide attack on the Ketene carbonyl carbon. [{Cp2ErNHEt}2] reacts with an excess of PhEtCCO to give [(Cp2Er{PhEtCHCON(Et)COCEtPh})2] (7), revealing another unique pattern of double-insertion of Ketenes into the metal–ligand bond without bond formation between two Ketene molecules. All complexes were characterized by elemental analysis and by their spectroscopic properties. The structures of complexes 1 b, 2 a, 2 b, 5 a, 5 b, 6, and 7 were also determined through X-ray single-crystal diffraction analysis.
J.c. Pommelet - One of the best experts on this subject based on the ideXlab platform.
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Photoelectronic Study of the Flash Vacuum Pyrolysis (FVP) of Meldrum's Acid Derivatives: PE Spectra of (Alkoxymethylene)- and ((Alkylthio)methylene)Ketenes 1
Journal of the American Chemical Society, 1991Co-Authors: F. Chuburu, Sylvie Lacombe-lhoste, G. Pfister-guillouzo, A. Ben Cheik, J. Chuche, J.c. PommeletAbstract:The (methoxymethylene)Ketenes 6 and 7 and the cyclic alkylthio derivative 9, generated by flash-vacuum pyrolysis of the corresponding substituted derivatives of Meldrum's acid, were characterized in the gas phase by photoelectron spectroscopy (PES). The experimental IP's arising from the ejection of an electron from the πC=C orbitals were determined and were shown to agree with previous results on parent and (alkylmethylene)Ketenes. An interesting feature concerns the observation, for the methylmethoxy compound 7, of different interconverting products at each pyrolysis temperature. The analysis of the PE spectra of these compounds supports Wentrup's mechanism: at 733 K a (carboxyvinyl)Ketene 21 would be obtained which is converted at higher temperature (843 K) into the desired (methylmethoxymethylene)Ketene (7). This latter, on further increase of the temperature (923 K), would give rise to the vinylKetene 23.
Mamoru Koketsu - One of the best experts on this subject based on the ideXlab platform.
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the staudinger reaction with 2 imino 1 3 thiaselenanes toward the synthesis of c4 spiro β lactams
Organic and Biomolecular Chemistry, 2013Co-Authors: Yosuke Toyoda, Masahiro Ebihara, Masayuki Ninomiya, Mamoru KoketsuAbstract:The Staudinger Ketene–imine [2 + 2] cycloaddition reaction for conversion of α-heteroatom-substituted exocyclic imines to C4 heterocyclic spiro-β-lactams has rarely been investigated due to their instability. Herein, we describe the Staudinger reaction between Ketenes and α-selenium-substituted exocyclic imines to synthesize C4 spiro-β-lactams.
