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Momen R, Azizi A, Morales-Bayuelo A, Pazhoohesh M, Ji X. New insights of QTAIM and stress tensor to finding non-competitive/competitive torquoselectivity of cyclobutene. J Chem Phys 2021; 155:204305. [PMID: 34852485 DOI: 10.1063/5.0068694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
This study aims to investigate the phenomenon of torquoselectivity through three thermal cyclobutene ring-opening reactions (N1-N3). This research focuses on the nature of the chemical bond, electronic reorganization, predicting non-competitive or competitive reactions, and torquoselectivity preference within Quantum Theory of Atoms in Molecules (QTAIM) and stress tensor frameworks. Various theoretical analyses for these reactions, such as metallicity ξ(rb), ellipticity ε, total local energy density H(rb), stress tensor polarizability ℙσ, stress tensor eigenvalue λ3σ, and bond-path length, display differently for non-competitive and competitive reactions as well as for the conrotatory preferences either it is the transition state outward conrotatory (TSout) or transition state inward conrotatory (TSin) directions by presenting degeneracy or non-degeneracy in their results. The ellipticity profile provides the motion of the bond critical point locations due to the different substituents of cyclobutene. In agreement with experimental results, examinations demonstrated that N1 is a competitive reaction and N2-N3 are non-competitive reactions with TSout and TSin preference directions, respectively. The concordant results of QTAIM and stress tensor scalar and vectors with experimental results provide a better understanding of reaction mechanisms.
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Affiliation(s)
- Roya Momen
- State Key Laboratory of Powder Metallurgy, College of Chemistry and Chemical Engineering, Central South University Changsha, Changsha 410083, China
| | - Alireza Azizi
- College of Material Science and Engineering, Central South University, Changsha, Hunan 410083, China
| | | | - Mehdi Pazhoohesh
- School of Engineering and Sustainable Development, De Montfort University, The Gateway, Leicester LE1 9BH, United Kingdom
| | - Xiaobo Ji
- State Key Laboratory of Powder Metallurgy, College of Chemistry and Chemical Engineering, Central South University Changsha, Changsha 410083, China
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2
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Wolf ME, Vandezande JE, Schaefer HF. Catalyzed reaction of isocyanates (RNCO) with water. Phys Chem Chem Phys 2021; 23:18535-18546. [PMID: 34612391 DOI: 10.1039/d1cp03302f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The reactions between substituted isocyanates (RNCO) and other small molecules (e.g. water, alcohols, and amines) are of significant industrial importance, particularly for the development of novel polyurethanes and other useful polymers. We present very high-level ab initio computations on the HNCO + H2O reaction, with results targeting the CCSDT(Q)/CBS//CCSD(T)/cc-pVQZ level of theory. Our results affirm that hydrolysis can occur across both the N[double bond, length as m-dash]C and C[double bond, length as m-dash]O bonds of HNCO via concerted mechanisms to form carbamate or imidic acid with ΔH0K barrier heights of 38.5 and 47.5 kcal mol-1. A total of 24 substituted RNCO + H2O reactions were studied. Geometries obtained with a composite method and refined with CCSD(T)/CBS single point energies determine that substituted RNCO species have a significant influence on these barrier heights, with an extreme case like fluorine lowering both barriers by close to 15 kcal mol-1 and most common alkyl substituents lowering both by approximately 3 kcal mol-1. Natural Bond Orbital (NBO) analysis provides evidence that the predicted barrier heights are strongly associated with the occupation of the in-plane C-O* orbital of the RNCO reactant. Key autocatalytic mechanisms are considered in the presence of excess water and RNCO species. Additional waters (one or two) are predicted to lower both barriers significantly at the CCSD(T)/aug-cc-pV(T+d)Z level of theory with strongly electron withdrawing RNCO substituents also increasing these effects, similar to the uncatalyzed case. The 298 K Gibbs energies are only marginally lowered by a second catalyst water molecule, indicating that the decreasing ΔH0K barriers are offset by loss of translational entropy with more than one catalyst water. Two-step 2RNCO + H2O mechanisms are characterized for the formation of carbamate and imidic acid. The second step of these two pathways exhibits the largest barrier and presents no clear pattern with respect to substituent choice. Our results indicate that an additional RNCO molecule might catalyze imidic acid formation but have less influence on the efficiency of carbamate formation. We expect that these results lay a firm foundation for the experimental study of substituted isocyanates and their relationship to the energetic pathways of related systems.
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Affiliation(s)
- Mark E Wolf
- Center for Computational Quantum Chemistry, University of Georgia, 140 Cedar Street, Athens, Georgia 30602, USA.
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3
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Novikov AS. Why [2 + 2]-cycloaddition reactions between isocyanates and imines do not occur in Pd-activation conditions? Inorganica Chim Acta 2020. [DOI: 10.1016/j.ica.2020.119758] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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4
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Abstract
A computational search has revealed concerted pathways for [2 + 2] cycloaddition of ethylene to all 10 of the cumulenes with the formula X═C═Y, where X, Y = C, N, O, and S. Four different concerted pathways have been found, three of them pseudopericyclic plus another based on sp-hybridized carbon. In the case of 2 of the 16 possible cycloadditions, a pair of novel three-membered ring intermediates has been discovered. As simple model reactions, cycloaddition of ethylene to formaldehyde, thioformaldehyde, and formaldimine is also described.
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Affiliation(s)
- David M Lemal
- Department of Chemistry, Dartmouth College , Hanover, New Hampshire 03755, United States
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5
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Porta EOJ, Vallejos MM, Bracca ABJ, Labadie GR. Experimental and theoretical studies of the [3,3]-sigmatropic rearrangement of prenyl azides. RSC Adv 2017. [DOI: 10.1039/c7ra09759j] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
[3,3]-Sigmatropic rearrangement of isoprenyl azides has been extensively investigated in an experimental and theoretical level.
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Affiliation(s)
| | - Margarita M. Vallejos
- Laboratorio de Química Orgánica
- IQUIBA-NEA
- Universidad Nacional del Nordeste
- CONICET
- FACENA
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6
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Barquera-Lozada JE. Torquoselectivity in Cyclobutene Ring Openings and the Interatomic Interactions That Control Them. J Phys Chem A 2016; 120:8450-8460. [PMID: 27723338 DOI: 10.1021/acs.jpca.6b08771] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Torquoselectivity has explained diasteromeric preferences of a number electrocyclic ring openings. The quantum theory of atoms in molecules (QTAIM), the electron localizability indicator (ELI-D), and the interacting quantum atoms (IQA) energy partition method are used to evaluate qualitatively and quantitatively the atomic interactions behind the torquoselectivity of a series of 3-substituted cyclobutenes. ELI-D topology and IQA energies show that the interaction between the distal terminus carbon atom of cyclobutene (C4) with the substituent at C3 (R5) in the transition state governs torquoselectivities. In the case of 3-borylcyclobutene, this interaction is so strong that a protocovalent bond is actually formed between B5 and C4. The evaluation of the interatomic energies allowed us to identify an additional interaction that contribute to a minor extent to the stabilization of the TS. Despite the fact that C4,R5 interaction is the main cause of the torquoselectivity, a bonding path (BP) between these two atoms was not observed. However, the lack of a BP between C4 and R5 does not mean that the topology of the electron density was not affected by the interaction of these two atoms. Surprisingly, we found a strong correlation between the density at the bond critical point (BCP) and the BP shape of C3-C4 breaking bond with the observed activation energies and torquoselectivities.
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Affiliation(s)
- José Enrique Barquera-Lozada
- Instituto de Química, Universidad Nacional Autónoma de México , Circuito exterior, Ciudad Universitaria Coyoacán, México, D.F., México 04510
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7
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Alcaide B, Almendros P, Cembellín S, Fernández I, Martínez del Campo T. Stereoselective synthesis of strained cage compounds via gold-catalyzed allene functionalization. Chem Commun (Camb) 2016; 52:10265-8. [DOI: 10.1039/c6cc03779h] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The diastereoselective synthesis of strained adducts that show cage-like structures has been accomplished directly from allenyl-β-lactams through gold catalysis. The sequence involving fragmentation of the β-lactam ring, isomerization of the allene moiety, and three consecutive carbocyclization reactions proceeds in a single operation.
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Affiliation(s)
- Benito Alcaide
- Grupo de Lactamas y Heterociclos Bioactivos
- Departamento de Química Orgánica
- Unidad Asociada al CSIC
- Facultad de Química
- Universidad Complutense de Madrid
| | - Pedro Almendros
- Instituto de Química Orgánica General
- IQOG-CSIC
- Juan de la Cierva 3
- 28006-Madrid
- Spain
| | - Sara Cembellín
- Grupo de Lactamas y Heterociclos Bioactivos
- Departamento de Química Orgánica
- Unidad Asociada al CSIC
- Facultad de Química
- Universidad Complutense de Madrid
| | - Israel Fernández
- Departamento de Química Orgánica I
- Facultad de Química
- Universidad Complutense de Madrid
- 28040 Madrid
- Spain
| | - Teresa Martínez del Campo
- Grupo de Lactamas y Heterociclos Bioactivos
- Departamento de Química Orgánica
- Unidad Asociada al CSIC
- Facultad de Química
- Universidad Complutense de Madrid
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8
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López CS, Faza ON, Freindorf M, Kraka E, Cremer D. Solving the Pericyclic–Pseudopericyclic Puzzle in the Ring-Closure Reactions of 1,2,4,6-Heptatetraene Derivatives. J Org Chem 2015; 81:404-14. [DOI: 10.1021/acs.joc.5b01997] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Carlos Silva López
- Departamento
de Química Orgánica, Campus Lagoas-Marcosende, 36310 Vigo, Spain
| | - Olalla Nieto Faza
- Departamento
de Química Orgánica, Campus Lagoas-Marcosende, 36310 Vigo, Spain
| | - Marek Freindorf
- Computational
and Theoretical Chemistry Group (CATCO), Department of Chemistry, Southern Methodist University, 3215 Daniel Avenue, Dallas, Texas 75275-0314, United States
| | - Elfi Kraka
- Computational
and Theoretical Chemistry Group (CATCO), Department of Chemistry, Southern Methodist University, 3215 Daniel Avenue, Dallas, Texas 75275-0314, United States
| | - Dieter Cremer
- Computational
and Theoretical Chemistry Group (CATCO), Department of Chemistry, Southern Methodist University, 3215 Daniel Avenue, Dallas, Texas 75275-0314, United States
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9
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Casarrubios L, Esteruelas MA, Larramona C, Lledós A, Muntaner JG, Oñate E, Ortuño MA, Sierra MA. Mechanistic Insight into the Facilitation of β-Lactam Fragmentation through Metal Assistance. Chemistry 2015; 21:16781-5. [DOI: 10.1002/chem.201503595] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Indexed: 11/07/2022]
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10
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Vallejos MM, Pellegrinet SC. Competing mechanisms for the reaction of dichloropropynylborane with 2-tert-butylbutadiene. Diels–Alder reaction versus alkynylboration. RSC Adv 2015. [DOI: 10.1039/c5ra12903f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Density functional theory and the quantum theory of atoms in molecules approach were used to study two competing process: the Diels–Alder reaction and the 1,4-alkynylboration.
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Affiliation(s)
- Margarita M. Vallejos
- Área de Química Orgánica
- Departamento de Química
- Facultad de Ciencias Exactas y Naturales y Agrimensura
- Universidad Nacional del Nordeste
- 3400 Corrientes
| | - Silvina C. Pellegrinet
- Instituto de Química Rosario (CONICET)
- Facultad de Ciencias Bioquímicas y Farmacéuticas
- Universidad Nacional de Rosario
- Rosario 2000
- Argentina
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11
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Vallejos MM, Grimblat N, Pellegrinet SC. Reactivity and selectivity of boron-substituted alkenes in the Diels-Alder reaction with cyclopentadiene. A study of the electron charge density and its Laplacian. J Phys Chem A 2014; 118:5559-70. [PMID: 24983836 DOI: 10.1021/jp504972r] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effect of the nature of the boron moiety upon the reactivity and the selectivity of a variety of vinylboron dienophiles (1-12) in the Diels-Alder (DA) reaction was investigated using density functional theory and the quantum theory of atoms in molecules. The calculated reactivity of the dienophiles decreases in the order vinylborane (1) > dihalovinylboranes (2-4) > dialkylvinylboranes (5-7) ≈ vinyl boronic acid (8) > vinylboronates (9, 10) > vinyl MIDA boronate (11) ≈ vinyltrifluoroborate (12). The DA reactions of 1-7 were slightly endo-selective due to the stronger C6-B secondary orbital interaction in the endo transition structures (TSs) evaluated by the C6|B delocalization index. In the TSs of 5 and 7, a combination of electronic and steric factors reduce the endo selectivity. The moderate exo selectivity calculated for the DA reactions of boronates 8-11 was attributed mainly to the hydrogen bond between the oxygen atom of boronate moieties and one of the acidic hydrogens of the methylene of cyclopentadiene in the exo TSs, which also reduces the ability of the oxygen lone pairs to donate electron density into the vacant boron orbital. Interestingly, the cooperative effect between the two hydrogen bonds in the exo TS of the DA reaction of vinyltrifluoroborate (12) determines the almost exclusive exo selectivity predicted for this DA reaction. We propose that the relative reactivities of the dienophiles can be estimated by the charge density (ρr) and its Laplacian (∇(2)ρr) at the (3,+1) critical point in the topology of ∇(2)ρr, evaluated at the reactant molecules in the ground state. The profiles of the several topological parameters along the reaction are affected by the nature of the substituents attached to the boron atom and by the mode of addition (endo and exo) in the DA reactions.
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Affiliation(s)
- Margarita M Vallejos
- Instituto de Quı́mica Rosario (CONICET), Facultad de Ciencias Bioquı́micas y Farmacéuticas, Universidad Nacional de Rosario , Suipacha 531, Rosario 2000, Argentina
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12
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Vallejos MM, Peruchena NM, Pellegrinet SC. [4 + 3] and [4 + 2] mechanisms of the Diels-Alder reactions of vinylboranes: an analysis of the electron charge density distribution. Org Biomol Chem 2013; 11:7953-65. [PMID: 24141322 DOI: 10.1039/c3ob41571f] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The Diels-Alder (DA) reactions of isoprene with vinylborane, dimethylvinylborane and dichlorovinylborane have been studied using density functional theory and the quantum theory of atoms in molecules. We evaluated the topological properties of the transition structures (TSs) and the evolution of such properties along the reaction paths. In accordance with previous studies, our results indicate that the endo TSs of the reaction with vinylborane present high [4 + 3] character, while the exo TSs and all the TSs of the reactions with dimethylvinylborane and dichlorovinylborane have [4 + 2] character. The higher charge concentration between the diene and the dienophile appears to account for the greater stabilization of the [4 + 3] TSs. The [4 + 3] structure turns into the [4 + 2] structure through a conflict mechanism in which the C1 and B atoms compete to become attached to C6. The C6-B interaction, present from early steps of the reaction until beyond the TSs, plays a key role in facilitating the formation of the new σ-bonds. The [4 + 3] and [4 + 2] mechanisms for the DA reactions of boron-substituted dienophiles may be distinguished by analyzing the profile of the ellipticity at the C1-C6 bcp along the course of the reaction.
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Affiliation(s)
- Margarita M Vallejos
- Instituto de Química Rosario (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, Rosario (2000), Argentina.
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13
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Theoretical investigations on the synthesis mechanism of cyanuric acid from NH3 and CO2. J Mol Model 2013; 19:5037-43. [DOI: 10.1007/s00894-013-2003-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Accepted: 09/08/2013] [Indexed: 11/30/2022]
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14
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Affiliation(s)
- Annette D. Allen
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Thomas T. Tidwell
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
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15
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Güizado-Rodríguez M, Ramírez-Galicia G. Electronic effect on the rotational barriers of PN bond in aminophosphanes. A theoretical approach. COMPUT THEOR CHEM 2012. [DOI: 10.1016/j.comptc.2012.05.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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16
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Cooperative effect of water molecules in the self-catalyzed neutral hydrolysis of isocyanic acid: a comprehensive theoretical study. J Mol Model 2010; 17:2069-82. [DOI: 10.1007/s00894-010-0917-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2010] [Accepted: 11/28/2010] [Indexed: 10/18/2022]
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17
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Zhang XH, Geng ZY. Reaction pathways of the [2+2] cycloaddition between formaldehyde with ketene and isocyanic acid: A theoretical investigation. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/j.theochem.2010.05.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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18
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A new specific mechanism for thioacid/azide amidation: electronic and solvent effects. OPEN CHEM 2010. [DOI: 10.2478/s11532-009-0139-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AbstractDetailed theoretical studies of azide/thioacid amidation are performed using density functional theory. The calculated results indicate that electronic properties of azide have significant effects on reaction pathways, which result in two distinct mechanisms for electron-rich and electron-poor azide coupling in the base-promoted amidation. For electron-rich azide amidation, after the concerted [3+2] cycloaddition of azide/thiocarboxylate, a new reaction channel is found challenging that recently mentioned, which follows two consecutive, unimolecular reactions with very low activation barriers (−1) to give an anionic amide and a nitrous sulfide (N2S). Distinct from electron-rich azide amidation, electron-poor azide first couples with thiocarboxylate to form a linear stable adduct, and then passes through the transition state of the rate-controlling step to afford the anionic amide, rather than the thiatrazoline. The free energy barrier of this step is 4.2 kcal mol−1 lower than that previously proposed. Comparatively, the azide/thioacid amidations undergo the concerted [3+2] cycloaddition and the subsequent retro-[3+2] cycloaddition process to give cis-enol form of the amide, which have higher activation barriers than those in the based-promoted amidation. Solvent effects investigated indicate that non-polar solvents, such as chloroform, are more preferable for the base-promoted thioacid/azide amidation.
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Gayatri G, Sastry GN. Estimating Regio and Stereoselectivity in [4+2] Cycloadditions of Vinyl-Substituted Cyclic Dienes with Maleic Anhydride. J Phys Chem A 2009; 113:12013-21. [DOI: 10.1021/jp9038072] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Gaddamanugu Gayatri
- Molecular Modeling Group, Organic Chemical Sciences, Indian Institute of Chemical Technology, Hyderabad-500607, India
| | - G. Narahari Sastry
- Molecular Modeling Group, Organic Chemical Sciences, Indian Institute of Chemical Technology, Hyderabad-500607, India
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20
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Ji H, Li L, Xu X, Ham S, Hammad LA, Birney* DM. Multiphoton Infrared Initiated Thermal Reactions of Esters: Pseudopericyclic Eight-Centered cis-Elimination. J Am Chem Soc 2008; 131:528-37. [DOI: 10.1021/ja804812c] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Hua Ji
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061
| | - Li Li
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061
| | - Xiaolian Xu
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061
| | - Sihyun Ham
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061
| | - Loubna A. Hammad
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061
| | - David M. Birney*
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061
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22
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Calvo-Losada S, Quirante Sánchez JJ. Pericyclic versus Pseudopericyclic Reactions. What the Laplacian of the Charge Density, ∇2ρ(r), Has To Say about It? The Case of Cycloaddition Reactions. J Phys Chem A 2008; 112:8164-78. [DOI: 10.1021/jp711565g] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Saturnino Calvo-Losada
- Departamento de Química Física, Facultad de Ciencias, Campus de Teatinos, s/n, Universidad de Málaga, 29071 Málaga, Spain
| | - J. J. Quirante Sánchez
- Departamento de Química Física, Facultad de Ciencias, Campus de Teatinos, s/n, Universidad de Málaga, 29071 Málaga, Spain
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23
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Rode JE, Dobrowolski JC. Variation of BCP ellipticities in the course of the pericyclic and pseudopericyclic [2+2] cycloaddition reactions of cumulenes. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.10.048] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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24
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Chamorro E, Notario R, Santos J, Pérez P. A theoretical scale for pericyclic and pseudopericyclic reactions. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.06.025] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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25
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Ramírez-Galicia G, Rubio MF, Jiménez-Cruz F. Intramolecular competition between alkenes in ketene–alkene [2+2] cycloaddition. A theoretical study. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/j.theochem.2006.06.030] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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