The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Paul A. Wender - One of the best experts on this subject based on the ideXlab platform.
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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.
Matthew C Stevens - One of the best experts on this subject based on the ideXlab platform.
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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.
Kuiling Ding - One of the best experts on this subject based on the ideXlab platform.
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highly regio and enantioselective alkoxycarbonylative amination of terminal Allenes catalyzed by a spiroketal based diphosphine pd ii complex
Journal of the American Chemical Society, 2015Co-Authors: Jiawang Liu, Zhaobin Han, Xiaoming Wang, Zheng Wang, Kuiling DingAbstract:An enantioselective alkoxycarbonylation-amination cascade process of terminal Allenes with CO, methanol, and arylamines has been developed. It proceeds under mild conditions (room temperature, ambient pressure CO) via oxidative Pd(II) catalysis using an aromatic spiroketal-based diphosphine (SKP) as a chiral ligand and a Cu(II) salt as an oxidant and affords a wide range of α-methylene-β-arylamino acid esters (36 examples) in good yields with excellent enantioselectivity (up to 96% ee) and high regioselectivity (branched/linear > 92:8). Preliminary mechanistic studies suggested that the reaction is likely to proceed through alkoxycarbonylpalladation of the Allene followed by an amination process. The synthetic utility of the protocol is showcased in the asymmetric construction of a cycloheptene-fused chiral β-lactam.
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Highly Regio- and Enantioselective Alkoxycarbonylative Amination of Terminal Allenes Catalyzed by a Spiroketal-Based Diphosphine/Pd(II) Complex
2015Co-Authors: Jiawang Liu, Zhaobin Han, Xiaoming Wang, Zheng Wang, Kuiling DingAbstract:An enantioselective alkoxycarbonylation–amination cascade process of terminal Allenes with CO, methanol, and arylamines has been developed. It proceeds under mild conditions (room temperature, ambient pressure CO) via oxidative Pd(II) catalysis using an aromatic spiroketal-based diphosphine (SKP) as a chiral ligand and a Cu(II) salt as an oxidant and affords a wide range of α-methylene-β-arylamino acid esters (36 examples) in good yields with excellent enantioselectivity (up to 96% ee) and high regioselectivity (branched/linear > 92:8). Preliminary mechanistic studies suggested that the reaction is likely to proceed through alkoxycarbonylpalladation of the Allene followed by an amination process. The synthetic utility of the protocol is showcased in the asymmetric construction of a cycloheptene-fused chiral β-lactam
John Montgomery - One of the best experts on this subject based on the ideXlab platform.
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The Mechanism of Copper-Catalyzed Trifunctionalization of Terminal Allenes
WILEY-V C H VERLAG GMBH, 2019Co-Authors: Hong Ki Kim, John Montgomery, Manoj V. Mane, Mu Hyun BaikAbstract:A highly selective copper-catalyzed trifunctionalization of Allenes has been established based on diborylation/cyanation with bis(pinacolato)diboron (B 2 pin 2 ) and N-cyano-N-phenyl-p-toluenesulfonamide (NCTS). The Cu-catalyzed trifunctionalization of terminal Allenes is composed of three catalytic reactions (first borocupration, electrophilic cyanation, and second borocupration) that provide a densely functionalized product with regio-, chemo- and diastereoselectivity. Allene substrates have multiple reaction-sites, and the selectivities are determined by the suitable interactions (e.g., electronic and steric demands) between the catalyst and substrates. We employed DFT calculations to understand the cascade copper-catalyzed trifunctionalization of terminal Allenes, providing densely-functionalized organic molecules with outstanding regio-, chemo- and diastereoselectivity in high yields. The selectivity challenges presented by cumulated π-systems are addressed by systematic computational studies; these give insight to the catalytic multiple-functionalization strategies and explain the high selectivities that we see for these reactions. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei
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Regioselective Allene Hydroarylation via One-Pot Allene Hydrosilylation/Pd-Catalyzed Cross-Coupling
2016Co-Authors: Zachary D Miller, John MontgomeryAbstract:ABSTRACT: Advances in hydroarylation have been achieved by the development of a one-pot regioselective Allene hydrosilylation/Pd(0)-catalyzed cross-coupling protocol. The regioselectivity is primarily governed by N-heterocyclic carbene (NHC) ligand identity in the hydrosilylation step and is preserved in the subsequent cross-coupling reaction. This methodology affords streamlined access to functionalized 1,1-disubstituted alkenes with excellent regiocontrol. Alkenylsilanes are versatile nucleophiles in metal-catalyzedcross-coupling reactions. Numerous carbon−carbon bond-forming reactions with alkenylsilanes have been well developed,1 including the powerful cross-coupling methodology extensively developed by Hiyama and Denmark.2−4 Currently, the most direct routes to alkenylsilanes are via metal-catalyzed hydro-silylations of alkynes.5 However, subtle alterations in the π-component, silane coupling partner, and metal catalyst often have substantial effects on the reaction outcome, leading t
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regioselective Allene hydroarylation via one pot Allene hydrosilylation pd catalyzed cross coupling
ChemInform, 2015Co-Authors: Zachary D Miller, John MontgomeryAbstract:The use of the extremely bulky NHC-ligand allows excellent regiocontrol in Allene hydrosilylations.
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regioselective Allene hydroarylation via one pot Allene hydrosilylation pd catalyzed cross coupling
Organic Letters, 2014Co-Authors: Zachary D Miller, John MontgomeryAbstract:Advances in hydroarylation have been achieved by the development of a one-pot regioselective Allene hydrosilylation/Pd(0)-catalyzed cross-coupling protocol. The regioselectivity is primarily governed by N-heterocyclic carbene (NHC) ligand identity in the hydrosilylation step and is preserved in the subsequent cross-coupling reaction. This methodology affords streamlined access to functionalized 1,1-disubstituted alkenes with excellent regiocontrol.
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...