The Experts below are selected from a list of 999 Experts worldwide ranked by ideXlab platform
Kendall N. Houk - One of the best experts on this subject based on the ideXlab platform.
-
DFT study of Pericyclic Reaction cascades in the synthesis of antibiotic TAN-1085.
Organic letters, 2004Co-Authors: Zeve R Akerling, Joseph E Norton, Kendall N. HoukAbstract:DFT calculations show that aromatic and bis-methoxy substituent effects in a synthetic precursor of TAN-1085 strongly favor a [1,7] sigmatropic hydrogen shift over the 6 pi electrocyclic pathway, rendering the latter unfavorable in synthesis.
-
Exploration of Pericyclic Reaction transition structures by quantum mechanical methods: competing concerted and stepwise mechanisms
Journal of Molecular Structure: THEOCHEM, 1997Co-Authors: Kendall N. Houk, Brett R. Beno, Kersey Black, Hi Young Yoo, Sarah Wilsey, Maja Nendel, Jeehiun K LeeAbstract:Density functional theory and multiconfigurational SCF calculations have been applied to a number of Pericyclic Reactions, including cycloadditions, electrocyclizations and sigmatropic shifts. Emphasis is on the competition between concerted and stepwise mechanisms, comparisons of computed and experimental activation energies and isotope effects, and the performance of MP2, CASSCF and DFT calculations. Various diradical processes, such as the vinylcyclopropane rearrangement and cyclobutane isomerizations, were also studied to test the performance of DFT with diradical processes.
-
Theory of substituent effects on Pericyclic Reaction rates: Alkoxy substituents in the Claisen rearrangement
Journal of the American Chemical Society, 1997Co-Authors: Hi Young Yoo, Kendall N. HoukAbstract:Transition structures, activation energies, and Reaction energies were calculated by ab initio quantum mechanical methods for the Claisen rearrangements of five hydroxy-substituted allyl vinyl ethers. The RHF, DFT(Becke3LYP), and CASSCF methods with the 6-31G* basis set were carried out. There is good agreement with activation energies measured for alkoxy-substituted compounds. The activation energies were separated into thermodynamic and intrinsic effects using Marcus theory as adapted by Murdoch for Pericyclic Reactions. Intrinsic effects were analyzed by frontier molecular orbital theory. The deuterium kinetic isotope effects calculated at the CASSCF/6-31G* level for the 2-OH allyl vinyl ether are in good agreement with the experimental results for the 2-OSiMe3 derivative, and these calculated isotope effects show much more bond-breaking and less bond-making than those at both the RHF/6-31G* and Becke3LYP/6-31G* levels.
-
Quantum Mechanical Methods and the Interpretation and Prediction of Pericyclic Reaction Mechanisms
The Journal of Physical Chemistry A, 1997Co-Authors: Olaf Wiest, And Daniel C. Montiel, Kendall N. HoukAbstract:The computational study of Pericyclic Reactions, an important general class of organic Reactions, now provides information about the transition structures of these processes with chemical accuracy, as judged by comparisons with experimental data, such as activation energies, substituent effects on rates, and kinetic isotope effects. This article introduces the methods used to study these Reactions and describes how computational results have contributed to the understanding of transition states and mechanisms of the electrocyclic ring openings of cyclobutenes, Diels−Alder cycloaddition Reactions, and [3,3]-sigmatropic shifts such as the Cope rearrangement.
Brian M Stoltz - One of the best experts on this subject based on the ideXlab platform.
-
the transition metal catalyzed π2s π2s σ2s σ2s Pericyclic Reaction woodward hoffmann rules aromaticity and electron flow
Journal of the American Chemical Society, 2020Co-Authors: Alexander Q Cusumano, William A Goddard, Brian M StoltzAbstract:We have shown that the fundamental step responsible for enantioinduction in the inner-sphere asymmetric Tsuji allylic alkylation is C–C bond formation through a seven-membered Pericyclic transition...
-
the transition metal catalyzed π2s π2s σ2s σ2s Pericyclic Reaction woodward hoffmann rules aromaticity and electron flow
Journal of the American Chemical Society, 2020Co-Authors: Alexander Q Cusumano, William A Goddard, Brian M StoltzAbstract:We have shown that the fundamental step responsible for enantioinduction in the inner-sphere asymmetric Tsuji allylic alkylation is C-C bond formation through a seven-membered Pericyclic transition state. We employ an extensive series of quantum mechanics (QM) calculations to delineate how the electronic structure of the Pd-catalyzed C-C bond forming process controls the Reaction. Phase inversion introduced by d orbitals renders the Pd-catalyzed [π2s + π2s + σ2s + σ2s] Reaction symmetry-allowed in the ground state, proceeding through a transition state with Craig-Mobius-like σ-aromaticity. Lastly, we connect QM to fundamental valence bonding concepts by deriving an ab initio "arrow-pushing" mechanism that describes the flow of electron density through the Reaction.
David C Clary - One of the best experts on this subject based on the ideXlab platform.
-
theoretical study of gas phase unimolecular decomposition of simulants of the nerve agent vx
Journal of Physical Chemistry A, 2019Co-Authors: Xiao Shan, Mark R Sambrook, David C ClaryAbstract:In order to further understand and support approaches for the degradation and destruction of toxic chemicals, the thermal decomposition of the nerve agent VX through possible Pericyclic hydrogen transfer Reactions is investigated using simulant molecules. A total of four simulant molecules are studied. Three of them have only one possible H-transfer site, while the other has two. They are chosen to bring physical insights into individual steps of the Pericyclic Reaction mechanism as well as the possible existence of competing mechanisms. The unimolecular Reaction rate constants at the high-pressure limit are calculated. Geometries of stationary structures on the potential energy surfaces are calculated with the MP2 method as well as the B3LYP and M06-2X functionals and 6-311++G(d,p), jul-cc-pVTZ, and aug-cc-pVTZ basis sets. The barrier heights are corrected using energy values obtained at the CBS/QB3 level of theory. The contribution of the quantum tunneling effect to the Reaction rate constants is included using one-dimensional semiclassical transition state theory. Adiabatic barrier heights, Reaction rate constants, and branching ratio of the competing mechanisms are reported.
-
Theoretical Study of Gas-Phase Unimolecular Decomposition of Simulants of the Nerve Agent VX
2018Co-Authors: Xiao Shan, Mark R Sambrook, David C ClaryAbstract:In order to further understand and support approaches for the degradation and destruction of toxic chemicals, the thermal decomposition of the nerve agent VX through possible Pericyclic hydrogen transfer Reactions is investigated using simulant molecules. A total of four simulant molecules are studied. Three of them have only one possible H-transfer site, while the other has two. They are chosen to bring physical insights into individual steps of the Pericyclic Reaction mechanism as well as the possible existence of competing mechanisms. The unimolecular Reaction rate constants at the high-pressure limit are calculated. Geometries of stationary structures on the potential energy surfaces are calculated with the MP2 method as well as the B3LYP and M06-2X functionals and 6-311++G(d,p), jul-cc-pVTZ, and aug-cc-pVTZ basis sets. The barrier heights are corrected using energy values obtained at the CBS/QB3 level of theory. The contribution of the quantum tunneling effect to the Reaction rate constants is included using one-dimensional semiclassical transition state theory. Adiabatic barrier heights, Reaction rate constants, and branching ratio of the competing mechanisms are reported
-
a combined theoretical and experimental study of sarin gb decomposition at high temperatures
Journal of Physical Chemistry A, 2017Co-Authors: Xiao Shan, Jack C Vincent, Sue Kirkpatrick, Maurice D Walker, Mark R Sambrook, David C ClaryAbstract:Theoretical and experimental results are presented for the pyrolytic decomposition of the nerve agent sarin (GB) in the gas phase. High-level quantum chemistry calculations are performed together with a semiclassical transition-state theory for describing quantum mechanical tunneling. The experimental and theoretical results for the temperature dependence of the survival times show very good agreement, as does the calculated and measured activation energy for thermal decomposition. The combined results suggest that the thermal decomposition of GB, for temperature ranging from 350 to 500 °C, goes through a Pericyclic Reaction mechanism with a transition state consisting of a six-membered ring structure.
K N Houk - One of the best experts on this subject based on the ideXlab platform.
-
origins of selectivity in Pericyclic Reaction cascades for the synthesis of gambogin and lateriflorone
Organic Letters, 2006Co-Authors: Amy E Hayden, K C Nicolaou, K N HoukAbstract:Quantum mechanical calculations demonstrate that the second step of a Claisen−Diels−Alder Reaction cascade controls regioselectivity that gives advanced intermediates for the synthesis of gambogin and 1-O-methyllateriflorone.
-
the performance of the handy cohen functionals olyp and o3lyp for the computation of hydrocarbon Pericyclic Reaction activation barriers
Journal of Physical Chemistry A, 2004Co-Authors: Vildan Guner, K N Houk, Kelli S Khuong, Anthony Chuma, Peter PulayAbstract:The performance of two local exchange functionals, OLYP and O3LYP, developed by Handy and Cohen (Mol. Phys. 2001, 99, 403), has been assessed for predicting activation barriers and Reaction energies for a set of eleven Pericyclic Reactions for which experimental data are well established. The results are compared to B3LYP and CBS-QB3 results previously reported (Guner et al. J. Phys. Chem. A 2003, 107, 11445).
-
5 5 sigmatropic rearrangement dft prediction of a diradical mechanism for a woodward hoffmann allowed thermal Pericyclic Reaction
Journal of the American Chemical Society, 1998Co-Authors: Brett R. Beno, K N Houk, Jens Fennen, Hans Jorg Lindner, Klaus HafnerAbstract:The mechanisms of the degenerate [5,5] sigmatropic rearrangements of 5,5a,10,10a-tetrahydroheptalene and (Z,Z)-1,3,7,9-decatetraene were explored with restricted and unrestricted Becke3LYP/6-31G* hybrid HF-DFT calculations. The restricted DFT wavefunctions for the synchronous, concerted transition structures for these formally Woodward−Hoffmann allowed 10-electron rearrangements are unstable with respect to unrestricted wavefunctions. A stepwise diradical mechanism is predicted for both Reactions. The 9 kcal/mol preference for the [5s,5s] mechanism over the [5a,5a] pathway in the rearrangement of decatetraene results primarily from the geometric distortions that the system must adopt in the [5a,5a] transition structure. The geometric and electronic characteristics of the [5,5] and [3,3] (Cope) rearrangements are compared.
Kazunobu Harano - One of the best experts on this subject based on the ideXlab platform.
-
Pericyclic Reaction behavior of cyclopentadienones toward acyclic conjugated dienes 3 3 sigmatropic rearrangement and double diels alder Reactions of the endo 4 2 π cycloadducts
ChemInform, 2010Co-Authors: Tamaki Jikyo, Masashi Eto, Kazunobu HaranoAbstract:Cycloaddition of 2, 5-disubstituted-3, 4-diphenylcyclopentadienone with acyclic conjugated dienes gave the endo [4+2]π cycloadducts, which then underwent [3, 3]-sigmatropic rearrangement to give the corresponding endo [2+4]π cycloadduct on heating at 110°C. Pyrolysis of the endo [4+2]π cycloadducts at 170°C resulted in decarbonylation to give the double Diels-Alder adduct. The sequential Pericyclic Reaction behavior is discussed on the basis of X-ray diffraction analyses and molecular orbital calculation data.
-
Pericyclic Reaction of ketenes with cascade Reaction products of pyridine N-oxides and dipolarophiles. X-ray structures of the adducts and formation mechanism.
Chemical & pharmaceutical bulletin, 2003Co-Authors: Shigeru Oiso, Masato Eto, Yasuyuki Yoshitake, Kazunobu HaranoAbstract:The structures of the adducts derived from the Reactions of substituted ketenes with dihydropyridine derivatives have been clarified by single crystal X-ray analyses and the formation mechanism is discussed on the basis of the Reaction-path calculations by semiempirical and density functional theory (DFT) molecular orbital methods.
-
cyclization of electron deficient cyclopentadienone with 2 alkenyl and 2 alkynylamines via sequential Pericyclic Reaction pathway
Journal of Organic Chemistry, 2001Co-Authors: Yasuyuki Yoshitake, Tamaki Jikyo, Kouki Yamaguchi, Chika Kai, Takayo Akiyama, Chiaki Handa, Kazunobu HaranoAbstract:The Pericyclic Reactions of 2,5-bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1a) with both allylic and propargylic amines have been investigated. The Reaction proceeded via initial formation of the 1,4 adducts followed by the ene cyclization and/or sequential Pericyclic Reactions depending upon the structures of the amines. The Reaction of 1a with diallylamine (2a) gave the tetracyclic compound (3a). On the other hand, the Reaction of 1a with 2-propynylamine (2c) gave exclusively the bicyclic compound (5c). In the Reactions with the secondary 2-propynylamines (2d,e), the tetracyclic compounds (3d,e) were exclusively formed. The Reactions of 1a with α-branched primary 1,1-dialkyl-2-propynylamines (2f,g) gave mixtures of 3- and 5-type compounds. The tetracyclic compounds 3 were formed from the intramolecular [4+2]π cycloadditions of the [1,5]-sigmatropic rearrangement products of the 1,4 adducts of 1a and 2, followed by the [1,5]-sigmatropic rearrangement of hydrogen and dehydrogenation. The bicyclic...
-
Sequential Pericyclic Reaction of unsaturated xanthates. Intramolecular cycloaddition selectivity of the 2,4-alkadienyl 2-alkenyl sulfides
Tetrahedron, 1996Co-Authors: Masato Eto, Toshihiro Uemura, Noriko Shimizu, Kazunobu HaranoAbstract:Heating of S-(1-vinyl-2-alkenyl) S-(2-alkenyl or alkynyl) dithiocarbonates (dithiolcarbonates) derived from [3,3]-sigmatropic rearrangement of O-(2,4-alkadienyl) S-(2-alkenyl or alkynyl) dithiocarbonates (xanthates) gave the 2,4-alkadienyl 2'-(alkenyl or alkynyl) sulfides, which then underwent intramolecular Diels-Alder cycloaddition to give hydrobenzo[c]thiophene derivatives. The thermal cyclization of O-(2,4-pentadienyl) derivatives of xanthate afforded mixtures of the cycloadducts, in which the cis-FUSED products slightly predominated over the trans-isomers. The selectivity of IMDA Reactions is discussed based on the ab initio calculation data.
-
Reaction of aromatic N-oxides with dipolarophiles. Part 18. Formation mechanism and X-ray structure of the cycloadduct from sequential Pericyclic Reaction of pyridine N-oxides with phenylsulfonylallene
Journal of the Chemical Society, Perkin Transactions 2, 1993Co-Authors: Toshikazu Matsuoka, Tomoaki Hasegawa, Masato Eto, Kazunobu Harano, Takuzo HisanoAbstract:Sequential Pericyclic Reactions of pyridine N-oxides (1) with phenylsulfonylpropadiene (2) and 1-phenylsulfonylpropyne (3) were investigated. 3,5-Dimethylpyridine N-oxide (la) was allowed to react with 2 in CHCl3 at room temperature to give a mixture of the [1,5]-sigmatropic rearrangement product (4a) of the 1 : 1 cycloadduct and the 1 : 2 azetidine-type cycloadduct (5a). The structure of 5a was established by single crystal X-ray analysis. The Reaction rate of 1a with 2 was about 50 000 times that of 1a with N-phenylmaleimide. The Reaction of 1a with 3 did not give 5a but 4a as the sole product. The reactivity, regio- and peri-selectivity and formation mechanism of 4 and 5 are discussed in terms of the frontier molecular orbital consideration based on kinetic and molecular orbital calculation data.