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Chien-hong Cheng - One of the best experts on this subject based on the ideXlab platform.
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synthesis of 1 2 dihydroquinolines by co iii catalyzed 3 3 annulation of anilides with benzylAllenes
ACS Catalysis, 2018Co-Authors: Ramajayam Kuppusamy, Rajagopal Santhoshkumar, Ramadoss Boobalan, Chien-hong ChengAbstract:A cobalt-catalyzed C–H/N–H annulation of anilides with Allenes to synthesize 1,2-dihydroquinolines is described. The reaction proceeds via a C–H activation, allene insertion, followed by β-hydride elimination and an intramolecular 1,4-addition to a butadiene-group-containing intermediate. Allenes act as a three-carbon source in the present C–H activation strategy.
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Synthesis of 1,2-Dihydroquinolines by Co(III)-Catalyzed [3 + 3] Annulation of Anilides with BenzylAllenes
2018Co-Authors: Ramajayam Kuppusamy, Rajagopal Santhoshkumar, Ramadoss Boobalan, Chien-hong ChengAbstract:A cobalt-catalyzed C–H/N–H annulation of anilides with Allenes to synthesize 1,2-dihydroquinolines is described. The reaction proceeds via a C–H activation, allene insertion, followed by β-hydride elimination and an intramolecular 1,4-addition to a butadiene-group-containing intermediate. Allenes act as a three-carbon source in the present C–H activation strategy
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Cobalt- and nickel-catalyzed regio- and stereoselective reductive coupling of alkynes, Allenes, and alkenes with alkenes.
Chemistry: A European Journal, 2008Co-Authors: Masilamani Jeganmohan, Chien-hong ChengAbstract:: Transition-metal-catalyzed coupling of two different C-C pi components through a metallacycle intermediate is a highly atom economical method to construct C-C bonds in organic synthesis. The metal-catalyzed coupling of an alkene and alkyne generally gives an Alder-ene or reductive coupling product. In this article, we focus on the cobalt- and nickel-catalyzed reductive coupling of alkynes, Allenes, and alkenes with alkenes. These reductive coupling reactions provide convenient methods for the synthesis of various alkenes, dienes, functionalized alkanes, lactones, lactams, and cyclic alcohols in a highly regio- and stereoselective manner. A chemselective formation of metallacyclopentene intermediate from the two different C-C pi components and a low-valence metal species plays a key role for the high regio- and stereoselectivity of the catalytic reaction.
Michael Schmittel - One of the best experts on this subject based on the ideXlab platform.
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the photochemical c2 c6 cyclization of enyne Allenes interception of the fulvene diradical with a radical clock ring opening
Journal of Organic Chemistry, 2009Co-Authors: Gotz Bucher, Atul A Mahajan, Michael SchmittelAbstract:The mechanism of the photochemical C(2)-C(6) cyclization of enyne-Allenes has been studied through radical clock, intramolecular kinetic isotope effect, and laser flash photolysis (LFP) experiments as well as density functional theory (DFT) and ab initio computations. While the photochemical cyclization of enyne-Allenes 1 and 2 furnished ene and Diels-Alder products without any cyclopropyl ring opening, that of 3 carrying the ultrafast diphenylcyclopropylcarbinyl radical clock afforded products derived from cyclopropyl ring opening. Laser flash photolysis (LFP) studies on enyne-allene 3 point to an allene triplet excited state (transient A) as a primarily formed short-lived (tau = 430 ns) intermediate. In addition, we have obtained evidence for the formation of a diphenylmethyl-type diradical (transient C, tau = 1.0 micros) resulting from ring opening of a diphenylcyclopropane ring. C subsequently undergoes a surprisingly slow (tau = 1.0 micros) 1,6-hydrogen shift leading to the stable 1,3-diene 6.
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photochemical c2 c6 cyclization of enyne Allenes detection of a fulvene triplet diradical in the laser flash photolysis
Journal of Organic Chemistry, 2008Co-Authors: Gotz Bucher, Atul A Mahajan, Michael SchmittelAbstract:A series of enyne−Allenes, with and without benzannulation at the ene moiety and equipped with aromatic and carbonyl groups as internal triplet sensitizer units at the allene terminus, was synthesized. Both sets, the cyclohexenyne−Allenes and benzenyne−Allenes, underwent thermal C2−C6 cyclization exclusively to formal ene products. In contrast, the photochemical C2−C6 cyclization of enyne−Allenes provided formal Diels−Alder and/or ene products, with higher yields for the benzannulated systems. A raise of the temperature in the photochemical cyclization of enyne−allene 1b′ led to increasing amounts of the ene product in relation to that of the formal Diels−Alder product. Laser flash photolysis at 266 and 355 nm as well as triplet quenching studies for 1b,b′ indicated that the C2−C6 cyclization proceeds via the triplet manifold. On the basis of a density functional theory (DFT) study, a short-lived transient (τ = 30 ns) was assigned as a triplet allene, while a long-lived transient (τ = 33 μs) insensitive t...
K N Houk - One of the best experts on this subject based on the ideXlab platform.
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Intercepting fleeting cyclic Allenes with asymmetric nickel catalysis
Nature, 2020Co-Authors: Michael M. Yamano, K N Houk, Andrew V. Kelleghan, Qianzhen Shao, Maude Giroud, Bryan J. Simmons, Shuming Chen, Neil K. GargAbstract:Strained cyclic organic molecules, such as arynes, cyclic alkynes and cyclic Allenes, have intrigued chemists for more than a century with their unusual structures and high chemical reactivity^ 1 . The considerable ring strain (30–50 kilocalories per mole)^ 2 , 3 that characterizes these transient intermediates imparts high reactivity in many reactions, including cycloadditions and nucleophilic trappings, often generating structurally complex products^ 4 . Although strategies to control absolute stereochemistry in these reactions have been reported using stoichiometric chiral reagents^ 5 , 6 , catalytic asymmetric variants to generate enantioenriched products have remained difficult to achieve. Here we report the interception of racemic cyclic allene intermediates in a catalytic asymmetric reaction and provide evidence for two distinct mechanisms that control absolute stereochemistry in such transformations: kinetic differentiation of allene enantiomers and desymmetrization of intermediate π-allylnickel complexes. Computational studies implicate a catalytic mechanism involving initial kinetic differentiation of the cyclic allene enantiomers through stereoselective olefin insertion, loss of the resultant stereochemical information, and subsequent introduction of absolute stereochemistry through desymmetrization of an intermediate π-allylnickel complex. These results reveal reactivity that is available to cyclic Allenes beyond the traditional cycloadditions and nucleophilic trappings previously reported, thus expanding the types of product accessible from this class of intermediates. Additionally, our computational studies suggest two potential strategies for stereocontrol in reactions of cyclic Allenes. Combined, these results lay the foundation for the development of catalytic asymmetric reactions involving these classically avoided strained intermediates. Asymmetric nickel catalysis is used to intercept transient cyclic allene intermediates to achieve stereocontrol.
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reactivity and chemoselectivity of Allenes in rh i catalyzed intermolecular 5 2 cycloadditions with vinylcyclopropanes allene mediated rhodacycle formation can poison rh i catalyzed cycloadditions
Journal of the American Chemical Society, 2014Co-Authors: Xin Hong, Paul A. Wender, Matthew C Stevens, Peng Liu, K N HoukAbstract:Allenes are important 2π building blocks in organic synthesis and engage as 2-carbon components in many metal-catalyzed reactions. Wender and co-workers discovered that methyl substituents on the terminal allene double bond counterintuitively change the reactivities of Allenes in [Rh(CO)2Cl]2-catalyzed intermolecular (5 + 2) cycloadditions with vinylcyclopropanes (VCPs). More sterically encumbered Allenes afford higher cycloadduct yields, and such effects are also observed in other Rh(I)-catalyzed intermolecular cycloadditions. Through density functional theory calculations (B3LYP and M06) and experiment, we explored this enigmatic reactivity and selectivity of Allenes in [Rh(CO)2Cl]2-catalyzed intermolecular (5 + 2) cycloadditions with VCPs. The apparent low reactivity of terminally unsubstituted Allenes is associated with a competing allene dimerization that irreversibly sequesters rhodium. With terminally substituted Allenes, steric repulsion between the terminal substituents significantly increases th...
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alkynes Allenes and alkenes in 3 3 sigmatropy functional diversity and kinetic monotony a theoretical analysis
Journal of the American Chemical Society, 1998Co-Authors: Kersey A Black, Sarah Wilsey, K N HoukAbstract:The [3,3]-sigmatropic shifts of 1,5-hexadiyne, 1,2-hexadien-5-yne, 1,2,5-hexatriene, 1,2,4,5-hexatetraene, and 1-hexen-5-yne were studied, using a hierarchy of methods (RHF/6-31G*, MP2//RHF/6-31G*, BLYP/6-31G*, Becke3LYP/6-31G*, and CASSCF/6-31G*). Hartree−Fock, MP2, and density functional methods predict the mechanisms to be concerted, involving aromatic transition structures, whereas CASSCF/6-31G* favors the stepwise pathways via diradical intermediates. Both MP2//RHF/6-31G* and Becke3LYP/6-31G* give activation energies in good agreement with the experimental values. Becke3LYP is a reliable tool for predicting the activation energies of such reactions, although it has a tendency to overstabilize allene systems. The activation energies for the series of reactions are remarkably constant at 31−35 kcal/mol, consistent with the aromatic character of their transition states. The origin of this kinetic monotony even in the face of structural diversity is analyzed.
Paul A. Wender - One of the best experts on this subject based on the ideXlab platform.
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Propargyltrimethylsilanes as Allene Equivalents in Transition Metal-
2016Co-Authors: Catalyzed Cycloadditions, Paul A. Wender, Fuyuhiko Inagaki, Magnus Pfaffenbach, Matthew C StevensAbstract:ABSTRACT: Conventional Allenes have not been effective π-reactive 2-carbon components in many intermolecular cyclo-additions including metal-catalyzed [5 + 2] cycloadditions. We report herein that rhodium-catalyzed [5 + 2] cycloadditions of propargyltrimethylsilanes and vinylcyclopropanes provide, after in situ protodesilylation, a highly efficient route to formal allene cycloadducts. Propargyltrimethylsilanes function as safe, easily handled synthetic equivalents of gaseous Allenes and hard-to-access monosubstituted Allenes. In this one-flask procedure, they provide cycloadducts of what is formally addition to the more sterically encumbered allene double bond. Since its introduction in 1995, the metal-catalyzed [5 + 2]cycloaddition of vinylcyclopropanes (VCPs) and π-systems, the homologous Diels−Alder reaction, has been shown to work intramolecularly with alkynes, alkenes, and Allenes and successfully applied to step-economical syntheses of various seven-membered ring-containing natural products.1,2 In con-trast, the intermolecular reaction has proven to be less general, working only with rhodium catalysts and being limited thus fa
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reactivity and chemoselectivity of Allenes in rh i catalyzed intermolecular 5 2 cycloadditions with vinylcyclopropanes allene mediated rhodacycle formation can poison rh i catalyzed cycloadditions
Journal of the American Chemical Society, 2014Co-Authors: Xin Hong, Paul A. Wender, Matthew C Stevens, Peng Liu, K N HoukAbstract:Allenes are important 2π building blocks in organic synthesis and engage as 2-carbon components in many metal-catalyzed reactions. Wender and co-workers discovered that methyl substituents on the terminal allene double bond counterintuitively change the reactivities of Allenes in [Rh(CO)2Cl]2-catalyzed intermolecular (5 + 2) cycloadditions with vinylcyclopropanes (VCPs). More sterically encumbered Allenes afford higher cycloadduct yields, and such effects are also observed in other Rh(I)-catalyzed intermolecular cycloadditions. Through density functional theory calculations (B3LYP and M06) and experiment, we explored this enigmatic reactivity and selectivity of Allenes in [Rh(CO)2Cl]2-catalyzed intermolecular (5 + 2) cycloadditions with VCPs. The apparent low reactivity of terminally unsubstituted Allenes is associated with a competing allene dimerization that irreversibly sequesters rhodium. With terminally substituted Allenes, steric repulsion between the terminal substituents significantly increases th...
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propargyltrimethylsilanes as allene equivalents in transition metal catalyzed 5 2 cycloadditions
Organic Letters, 2014Co-Authors: Paul A. Wender, Fuyuhiko Inagaki, Magnus Pfaffenbach, Matthew C StevensAbstract:Conventional Allenes have not been effective π-reactive 2-carbon components in many intermolecular cycloadditions including metal-catalyzed [5 + 2] cycloadditions. We report herein that rhodium-catalyzed [5 + 2] cycloadditions of propargyltrimethylsilanes and vinylcyclopropanes provide, after in situ protodesilylation, a highly efficient route to formal allene cycloadducts. Propargyltrimethylsilanes function as safe, easily handled synthetic equivalents of gaseous Allenes and hard-to-access monosubstituted Allenes. In this one-flask procedure, they provide cycloadducts of what is formally addition to the more sterically encumbered allene double bond.
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The Diene Effect: The Design, Development, and Mechanistic Investigation of Metal-Catalyzed Diene-yne, Diene-ene, and Diene-allene [2+2+1] Cycloaddition Reactions
European Journal of Organic Chemistry, 2009Co-Authors: Mitchell P. Croatt, Paul A. WenderAbstract:Metal-catalyzed diene-yne, diene-ene, and diene-allene [2+2+1] cycloaddition reactions provide new methods for the facile construction of highly functionalized five-membered rings. These reactions can be conducted with a variety of substrate substitution patterns and functional groups and often in the absence of solvent. The special reactivity of dienes, a key to enabling or enhancing the effectiveness of the [2+2+1] and other reactions, is significantly different from that of alkynes, alkenes, or Allenes. For example, the [2+2+1] reaction of a diene-yne is accelerated compared to that of the corresponding ene-yne. An even more dramatic "diene effect" is found with diene-enes and diene-Allenes. While bis-enes and ene-Allenes are not reported to yield [2+2+1] cycloadducts, the related diene-enes and diene-Allenes undergo efficient [2+2+1] cycloadditions, providing new routes to cyclopentanones and alkylidenecyclopentanones. Mechanistic studies suggest that the unique reactivity observed with dienes arises from their participation in the putative rate-determining reductive elimination step by providing an additional energy-lowering coordination site for the transition metal catalyst.
Gotz Bucher - One of the best experts on this subject based on the ideXlab platform.
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the photochemical c2 c6 cyclization of enyne Allenes interception of the fulvene diradical with a radical clock ring opening
Journal of Organic Chemistry, 2009Co-Authors: Gotz Bucher, Atul A Mahajan, Michael SchmittelAbstract:The mechanism of the photochemical C(2)-C(6) cyclization of enyne-Allenes has been studied through radical clock, intramolecular kinetic isotope effect, and laser flash photolysis (LFP) experiments as well as density functional theory (DFT) and ab initio computations. While the photochemical cyclization of enyne-Allenes 1 and 2 furnished ene and Diels-Alder products without any cyclopropyl ring opening, that of 3 carrying the ultrafast diphenylcyclopropylcarbinyl radical clock afforded products derived from cyclopropyl ring opening. Laser flash photolysis (LFP) studies on enyne-allene 3 point to an allene triplet excited state (transient A) as a primarily formed short-lived (tau = 430 ns) intermediate. In addition, we have obtained evidence for the formation of a diphenylmethyl-type diradical (transient C, tau = 1.0 micros) resulting from ring opening of a diphenylcyclopropane ring. C subsequently undergoes a surprisingly slow (tau = 1.0 micros) 1,6-hydrogen shift leading to the stable 1,3-diene 6.
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photochemical c2 c6 cyclization of enyne Allenes detection of a fulvene triplet diradical in the laser flash photolysis
Journal of Organic Chemistry, 2008Co-Authors: Gotz Bucher, Atul A Mahajan, Michael SchmittelAbstract:A series of enyne−Allenes, with and without benzannulation at the ene moiety and equipped with aromatic and carbonyl groups as internal triplet sensitizer units at the allene terminus, was synthesized. Both sets, the cyclohexenyne−Allenes and benzenyne−Allenes, underwent thermal C2−C6 cyclization exclusively to formal ene products. In contrast, the photochemical C2−C6 cyclization of enyne−Allenes provided formal Diels−Alder and/or ene products, with higher yields for the benzannulated systems. A raise of the temperature in the photochemical cyclization of enyne−allene 1b′ led to increasing amounts of the ene product in relation to that of the formal Diels−Alder product. Laser flash photolysis at 266 and 355 nm as well as triplet quenching studies for 1b,b′ indicated that the C2−C6 cyclization proceeds via the triplet manifold. On the basis of a density functional theory (DFT) study, a short-lived transient (τ = 30 ns) was assigned as a triplet allene, while a long-lived transient (τ = 33 μs) insensitive t...