The Experts below are selected from a list of 1455 Experts worldwide ranked by ideXlab platform
Wenjing Xiao - One of the best experts on this subject based on the ideXlab platform.
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sequential visible light photoactivation and palladium catalysis enabling enantioselective 4 2 cycloadditions
Journal of the American Chemical Society, 2017Co-Authors: Yi Wei, Jie Liu, Hongwei Chen, Wenjing XiaoAbstract:Catalytic asymmetric cycloadditions of reactive ketene intermediates provide new opportunities for the production of chiral heterocyclic molecules. Though known for over 100 years, Ketenes still remain underexplored in the field of transition-metal (TM)-catalyzed asymmetric cycloadditions because (1) Ketenes, as highly electron-deficient species, are possibly unstable to low-valence TMs (i.e., decarbonylation or aggregation) and (2) the conventional thermal synthesis of Ketenes from acyl chlorides and amines may be incompatible with TM catalysis (i.e., reactive acyl chloride and amine hydrochloride byproducts). Herein, we detail the unprecedented asymmetric [4+2] cycloaddition of vinyl benzoxazinanones with a variety of ketene intermediates via sequential visible-light photoactivation and palladium catalysis. It is well demonstrated that the traceless and transient generation of Ketenes from α-diazoketones through visible-light-induced Wolff rearrangement is important for the success of present cycloaddit...
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Sequential Visible-Light Photoactivation and Palladium Catalysis Enabling Enantioselective [4+2] Cycloadditions
2017Co-Authors: Yi Wei, Jie Liu, Hongwei Chen, Wenjing XiaoAbstract:Catalytic asymmetric cycloadditions of reactive ketene intermediates provide new opportunities for the production of chiral heterocyclic molecules. Though known for over 100 years, Ketenes still remain underexplored in the field of transition-metal (TM)-catalyzed asymmetric cycloadditions because (1) Ketenes, as highly electron-deficient species, are possibly unstable to low-valence TMs (i.e., decarbonylation or aggregation) and (2) the conventional thermal synthesis of Ketenes from acyl chlorides and amines may be incompatible with TM catalysis (i.e., reactive acyl chloride and amine hydrochloride byproducts). Herein, we detail the unprecedented asymmetric [4+2] cycloaddition of vinyl benzoxazinanones with a variety of ketene intermediates via sequential visible-light photoactivation and palladium catalysis. It is well demonstrated that the traceless and transient generation of Ketenes from α-diazoketones through visible-light-induced Wolff rearrangement is important for the success of present cycloaddition. Furthermore, chiral palladium catalysts with a new, chiral hybrid P, S ligand enable asymmetric cycloaddition with high reaction selectivity and enantiocontrol
Henry F. Schaefer - One of the best experts on this subject based on the ideXlab platform.
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formylmethylene the triplet ground state and the lowest singlet state
Journal of Physical Chemistry A, 2013Co-Authors: Jun Guan, Katherine R Randall, Huidong Li, Henry F. SchaeferAbstract:The ground triplet state and lowest singlet state of formylmethylene have been proposed as important intermediates in the Wolff rearrangement of α-diazo ketones into Ketenes. The ground triplet state of formylmethylene has been examined experimentally, but the lowest singlet state has yet to be observed. We predict equilibrium geometries, energies, bonding, dipole moments, and harmonic vibrational frequencies for these two lowest states of formylmethylene at the cc-pVQZ CCSD(T) level of theory. The singlet–triplet energy difference [ΔE(S-T)] is quite sensitive to the level of theory. The highly accurate cc-pVQZ CCSD(T) level of theory yields the most reliable result of only 2.0 kcal mol–1. An estimate based on the experimentally characterized CH2 molecule yields ΔE(S-T) = 1.27 kcal mol–1. In addition, accurate quartic force fields have been determined at the cc-pVTZ CCSD(T) level of theory. Fundamental vibrational frequencies, anharmonic constants, and vibration–rotation coupling constants were determined...
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formylmethylene the triplet ground state and the lowest singlet state
Journal of Physical Chemistry A, 2013Co-Authors: Jun Guan, Katherine R Randall, Huidong Li, Henry F. SchaeferAbstract:The ground triplet state and lowest singlet state of formylmethylene have been proposed as important intermediates in the Wolff rearrangement of α-diazo ketones into Ketenes. The ground triplet state of formylmethylene has been examined experimentally, but the lowest singlet state has yet to be observed. We predict equilibrium geometries, energies, bonding, dipole moments, and harmonic vibrational frequencies for these two lowest states of formylmethylene at the cc-pVQZ CCSD(T) level of theory. The singlet–triplet energy difference [ΔE(S-T)] is quite sensitive to the level of theory. The highly accurate cc-pVQZ CCSD(T) level of theory yields the most reliable result of only 2.0 kcal mol–1. An estimate based on the experimentally characterized CH2 molecule yields ΔE(S-T) = 1.27 kcal mol–1. In addition, accurate quartic force fields have been determined at the cc-pVTZ CCSD(T) level of theory. Fundamental vibrational frequencies, anharmonic constants, and vibration–rotation coupling constants were determined...
Yi Wei - One of the best experts on this subject based on the ideXlab platform.
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sequential visible light photoactivation and palladium catalysis enabling enantioselective 4 2 cycloadditions
Journal of the American Chemical Society, 2017Co-Authors: Yi Wei, Jie Liu, Hongwei Chen, Wenjing XiaoAbstract:Catalytic asymmetric cycloadditions of reactive ketene intermediates provide new opportunities for the production of chiral heterocyclic molecules. Though known for over 100 years, Ketenes still remain underexplored in the field of transition-metal (TM)-catalyzed asymmetric cycloadditions because (1) Ketenes, as highly electron-deficient species, are possibly unstable to low-valence TMs (i.e., decarbonylation or aggregation) and (2) the conventional thermal synthesis of Ketenes from acyl chlorides and amines may be incompatible with TM catalysis (i.e., reactive acyl chloride and amine hydrochloride byproducts). Herein, we detail the unprecedented asymmetric [4+2] cycloaddition of vinyl benzoxazinanones with a variety of ketene intermediates via sequential visible-light photoactivation and palladium catalysis. It is well demonstrated that the traceless and transient generation of Ketenes from α-diazoketones through visible-light-induced Wolff rearrangement is important for the success of present cycloaddit...
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Sequential Visible-Light Photoactivation and Palladium Catalysis Enabling Enantioselective [4+2] Cycloadditions
2017Co-Authors: Yi Wei, Jie Liu, Hongwei Chen, Wenjing XiaoAbstract:Catalytic asymmetric cycloadditions of reactive ketene intermediates provide new opportunities for the production of chiral heterocyclic molecules. Though known for over 100 years, Ketenes still remain underexplored in the field of transition-metal (TM)-catalyzed asymmetric cycloadditions because (1) Ketenes, as highly electron-deficient species, are possibly unstable to low-valence TMs (i.e., decarbonylation or aggregation) and (2) the conventional thermal synthesis of Ketenes from acyl chlorides and amines may be incompatible with TM catalysis (i.e., reactive acyl chloride and amine hydrochloride byproducts). Herein, we detail the unprecedented asymmetric [4+2] cycloaddition of vinyl benzoxazinanones with a variety of ketene intermediates via sequential visible-light photoactivation and palladium catalysis. It is well demonstrated that the traceless and transient generation of Ketenes from α-diazoketones through visible-light-induced Wolff rearrangement is important for the success of present cycloaddition. Furthermore, chiral palladium catalysts with a new, chiral hybrid P, S ligand enable asymmetric cycloaddition with high reaction selectivity and enantiocontrol
Miguel A. Sierra - One of the best experts on this subject based on the ideXlab platform.
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the photochemical reaction of vinylaziridines and vinylazetidines with chromium 0 and molybdenum 0 fischer carbene complexes
Chemistry: A European Journal, 2014Co-Authors: Alexandra R Rivero, Israel Fernandez, Miguel A. SierraAbstract:The [5+2] and [6+2] cycloaddition reactions of vinylaziridines and vinylazetidines with Ketenes generated photochemically from chromium(0) and molybdenum(0) Fischer carbene complexes have been investigated. These processes constitute a straightforward and efficient route to azepanones and azocinones, respectively. The peculiar electronic properties of the metalated Ketenes allow for the introduction of electron-rich substituents in the final cycloadducts, a difficult task using conventional organic chemistry procedures. The versatility of the process is demonstrated by using Cr(0) Fischer bis(carbene) complexes as metalated bis(ketene) precursors. These species produce tethered bis(azepanone)s in a single step under mild reaction conditions. Density functional theory calculations point to a stepwise reaction pathway through the initial nucleophilic attack of the nitrogen atom of the aziridine on the metalated ketene, followed by ring closure of the zwitterionic intermediate formed.
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the mechanism of the ketene imine staudinger reaction in its centennial still an unsolved problem
Accounts of Chemical Research, 2008Co-Authors: Fernando P Cossio, Ana Arrieta, Miguel A. SierraAbstract:Although Staudinger reported the reaction between Ketenes and imines 100 years ago (1907), this process is still the most general and useful method for the synthesis of β-lactams and their derivatives. This reaction is a [2 + 2] thermal cycloaddition in which two chiral centers may be generated in one preparative step. Staudinger reactions involving α,β-unsaturated imines or Ketenes have issues concerning the [2 + 2] or [4 + 2] periselectivity of the reaction. This Account discusses how the main factors that determine the regiochemical and stereochemical outcomes of this reaction were elucidated with computational and experimental data. This fruitful interplay between theory and experiment has revealed that the [2 + 2] cycloaddition is actually a two-step process. The first step is a nucleophilic addition of the nitrogen atom of the imine on the sp-hybridized carbon atom of the ketene. This attack forms a zwitterionic intermediate that evolves toward the final β-lactam cycloadduct. The second step can be ...
Jun Guan - One of the best experts on this subject based on the ideXlab platform.
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formylmethylene the triplet ground state and the lowest singlet state
Journal of Physical Chemistry A, 2013Co-Authors: Jun Guan, Katherine R Randall, Huidong Li, Henry F. SchaeferAbstract:The ground triplet state and lowest singlet state of formylmethylene have been proposed as important intermediates in the Wolff rearrangement of α-diazo ketones into Ketenes. The ground triplet state of formylmethylene has been examined experimentally, but the lowest singlet state has yet to be observed. We predict equilibrium geometries, energies, bonding, dipole moments, and harmonic vibrational frequencies for these two lowest states of formylmethylene at the cc-pVQZ CCSD(T) level of theory. The singlet–triplet energy difference [ΔE(S-T)] is quite sensitive to the level of theory. The highly accurate cc-pVQZ CCSD(T) level of theory yields the most reliable result of only 2.0 kcal mol–1. An estimate based on the experimentally characterized CH2 molecule yields ΔE(S-T) = 1.27 kcal mol–1. In addition, accurate quartic force fields have been determined at the cc-pVTZ CCSD(T) level of theory. Fundamental vibrational frequencies, anharmonic constants, and vibration–rotation coupling constants were determined...
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formylmethylene the triplet ground state and the lowest singlet state
Journal of Physical Chemistry A, 2013Co-Authors: Jun Guan, Katherine R Randall, Huidong Li, Henry F. SchaeferAbstract:The ground triplet state and lowest singlet state of formylmethylene have been proposed as important intermediates in the Wolff rearrangement of α-diazo ketones into Ketenes. The ground triplet state of formylmethylene has been examined experimentally, but the lowest singlet state has yet to be observed. We predict equilibrium geometries, energies, bonding, dipole moments, and harmonic vibrational frequencies for these two lowest states of formylmethylene at the cc-pVQZ CCSD(T) level of theory. The singlet–triplet energy difference [ΔE(S-T)] is quite sensitive to the level of theory. The highly accurate cc-pVQZ CCSD(T) level of theory yields the most reliable result of only 2.0 kcal mol–1. An estimate based on the experimentally characterized CH2 molecule yields ΔE(S-T) = 1.27 kcal mol–1. In addition, accurate quartic force fields have been determined at the cc-pVTZ CCSD(T) level of theory. Fundamental vibrational frequencies, anharmonic constants, and vibration–rotation coupling constants were determined...
