Computational study of one-step polar Diels–Alder reactions using the NEB method for the minimum energy paths search

2017 ◽  
Vol 43 (8) ◽  
pp. 644-655 ◽  
Author(s):  
Miguel A. Díaz ◽  
José G. Parra ◽  
David S. Coll
Keyword(s):  
Computational Study ◽  
Minimum Energy ◽  
Diels Alder ◽  
One Step ◽  
Minimum Energy Paths

Synthesis of bicyclic diones and thiones. Facile methylation of the enolates of bicyclo[2.2.1]heptane-2,5-dione and bicyclo[2.2.2]octane-2,5-dione. An AM1 computational study of bicyclic enolates

1992 ◽  
Vol 70 (3) ◽  
pp. 974-980 ◽  
Author(s):  
N. H. Werstiuk ◽  
S. Yeroushalmi ◽  
Hong Guan-Lin
Keyword(s):  
Raney Nickel ◽  
Good Yield ◽  
Computational Study ◽  
Alder Reaction ◽  
Diels Alder ◽  
Am1 Calculations ◽  
Diels Alder Reaction ◽  
Bicyclic Ketones ◽  
One Step

A group of bicyclic ketones and thiones have been synthesized for homenolization studies. Bicyclo[2.2.1]heptane-2,5-dione (6) undergoes unusually rapid tetramethylation giving 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dione (1) in good yield. Treatment of 1 with P2S5 in xylene gave 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dithione (2) and 3,3,6,6-tetramethyl 15-oxo-bicyclo[2.2.1]heptane-2-thione (3), which was converted into 4 with Raney nickel. Bicyclo[2,2,2]octane-2,5-dione (7), prepared via a Diels–Alder reaction between 2-trimethylsilyloxy-1,3-cyclohexadiene and and α-acetoxyacrylonitrile followed by a one-step desilylation/hydrolysis, also undergoes facile tetramethylation giving 3,3,6,6-tetramethylbicyclo[2.2.2]octane-2,5-dione (5) in good yield. AM1 calculations were carried out on the α-enolates of bicyclo[2.2.1]heptan-2-one, 6, 5-methylidenebicyclo[2.2.1]heptan-2-one, and 4-acetylbicyclo[2.2.1]-heptan-2-one in an attempt to gain information on the source of the enhanced acidity of the C-3 hydrogens of 6 and 7. Keywords: bicyclic ketones, thiones, synthesis.

On the generation of oxirene and dimethyloxirene by retro-Diels–Alder reactions, and reactions of dimethyloxirene: a computational study

2002 ◽  
Vol 80 (1) ◽  
pp. 94-105 ◽  
Author(s):  
C Delamere ◽  
C Jakins ◽  
E Lewars
Keyword(s):  
Transition State ◽  
Ring Opening ◽  
Computational Study ◽  
Single Point ◽  
Diels Alder ◽  
Reaction Energy ◽  
One Step ◽  
Reaction Energies ◽  
Level 1 ◽  
Late Transition

The isomerization of oxirene (oxacyclopropene) (1) to ketene, dimethyloxirene (7) to dimethylketene via the oxo carbene ("ketocarbene"), and the retro-Diels–Alder extrusion of oxirene and dimethyloxirene from their formal adducts (9 and 24, respectively) with benzene were studied computationally. All species were optimized at the MP2(fc)/6–31G(df,p) level; the species involving 1 were also subjected to MP2(fc)/6–31G(df,p) frequency and single-point CCSD(T)/6–31G(df,p) calculations. At the CCSD(T)/6–31G(df,p)//MP2(fc)/6–31G(df,p) level 1 isomerized to ketene in one step with a barrier of 2.8 kJ mol–1 and a reaction energy of –320.6 kJ mol–1. The extrusion of 1 from 9 had a late transition state and activation and reaction energies of 264.2 and 214.2 kJ mol–1, respectively, cf. cyclopropene extrusion from its adduct (192.3 and 95.9 kJ mol–1), indicating an antiaromatic destabilization energy of 214.2 – 95.9 = 118 kJ mol–1 for 1. The carbene 8 from ring-opening of 7 lay 10.9 kJ mol–1 above 7 (CCSD(T)/6–31G(df,p)//MP2(fc)/6–31G(df,p)), but the transition state could not be found; 8 isomerized to dimethylketene (252.7 kJ mol–1 below 7) with a barrier of 16.4 kJ mol–1, and to s-(Z)- and s-(E)-butenone with barriers of 28.5 and 35.4 kJ mol–1, respectively. The UV (TDDFT, B3P86/6–311++G**//MP2(fc)/6–31G(df,p)) spectra of 1 and 7 were calculated. Discrepancies were seen between the calculated IR spectra of 7 (bis(trifluoromethyl)oxirene) and perfluoro ethyl methyloxirene, and those attributed to these species in earlier matrix-isolation work. Key words: oxirene, dimethyloxirene, ab initio, retro-Diels–Alder, Diels–Alder.

scholarly journals Photoprotective Properties of Eumelanin: Computational Insights into the Photophysics of a Catechol:Quinone Heterodimer Model System

Photochem ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 26-37
Author(s):  
Victoria C. Frederick ◽  
Thomas A. Ashy ◽  
Barbara Marchetti ◽  
Michael N. R. Ashfold ◽  
Tolga N. V. Karsili
Keyword(s):  
Ground State ◽  
Sandwich Structure ◽  
Computational Study ◽  
Minimum Energy ◽  
Carbonyl Oxygen ◽  
Model System ◽  
Molecular Structures ◽  
Uv Damage ◽  
Chromosomal Dna ◽  
Relevant Model

Melanins are skin-centered molecular structures that block harmful UV radiation from the sun and help protect chromosomal DNA from UV damage. Understanding the photodynamics of the chromophores that make up eumelanin is therefore paramount. This manuscript presents a multi-reference computational study of the mechanisms responsible for the experimentally observed photostability of a melanin-relevant model heterodimer comprising a catechol (C)–benzoquinone (Q) pair. The present results validate a recently proposed photoinduced intermolecular transfer of an H atom from an OH moiety of C to a carbonyl-oxygen atom of the Q. Photoexcitation of the ground state C:Q heterodimer (which has a π-stacked “sandwich” structure) results in population of a locally excited ππ* state (on Q), which develops increasing charge-transfer (biradical) character as it evolves to a “hinged” minimum energy geometry and drives proton transfer (i.e., net H atom transfer) from C to Q. The study provides further insights into excited state decay mechanisms that could contribute to the photostability afforded by the bulk polymeric structure of eumelanin.

On the Mechanism of Au‐catalyzed Enynamide‐Yne Dehydro‐Diels‐Alder Reactions: An Experimental and Computational Study

2021 ◽  
Author(s):  
David Fabian León Rayo ◽  
Young J. Hong ◽  
Dominic Campeau ◽  
Dean J. Tantillo ◽  
Fabien Gagosz
Keyword(s):  
Computational Study ◽  
Diels Alder

scholarly journals Application of β-Phosphorylated Nitroethenes in [3+2] Cycloaddition Reactions Involving Benzonitrile N-Oxide in the Light of a DFT Computational Study

Organics ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 26-37
Author(s):  
Karolina Zawadzińska ◽  
Karolina Kula
Keyword(s):  
Density Functional ◽  
Reaction Path ◽  
Computational Study ◽  
Cyano Group ◽  
Cycloaddition Reactions ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Reaction Channels ◽  
One Step ◽  
Step Mechanism

The regiochemistry of [3+2] cycloaddition (32CA) processes between benzonitrile N-oxide 1 and β-phosphorylated analogues of nitroethenes 2a–c has been studied using the Density Functional Theory (DFT) at the M062X/6-31+G(d) theory level. The obtained results of reactivity indices show that benzonitrile N-oxide 1 can be classified both as a moderate electrophile and moderate nucleophile, while β-phosphorylated analogues of nitroethenes 2a–c can be classified as strong electrophiles and marginal nucleophiles. Moreover, the analysis of CDFT shows that for [3+2] cycloadditions with the participation of β-phosphorylatednitroethene 2a and β-phosphorylated α-cyanonitroethene 2b, the more favored reaction path forms 4-nitro-substituted Δ2-isoxazolines 3a–b, while for a reaction with β-phosphorylated β-cyanonitroethene 2c, the more favored path forms 5-nitro-substituted Δ2-isoxazoline 4c. This is due to the presence of a cyano group in the alkene. The CDFT study correlates well with the analysis of the kinetic description of the considered reaction channels. Moreover, DFT calculations have proven the clearly polar nature of all analyzed [3+2] cycloaddition reactions according to the polar one-step mechanism.

One-step Functionalization of Mildly and Strongly Reduced Graphene Oxide with Maleimide: An Experimental and Theoretical Investigation of the Diels-Alder [4+2] Cycloaddition Reaction

2021 ◽  
Author(s):  
Alfonso Ferretti ◽  
Sourab Sinha ◽  
Luca Sagresti ◽  
Esteban Araya-Hermosilla ◽  
Mirko Prato ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Reduced Graphene Oxide ◽  
Large Scale ◽  
Cycloaddition Reaction ◽  
Diels Alder ◽  
Reduced Form ◽  
Graphene Nanocomposites ◽  
Exfoliated Graphene ◽  
Reduced Graphene ◽  
One Step

For large-scale graphene applications, such as the production of polymer-graphene nanocomposites, exfoliated graphene oxide (GO) and its reduced form (rGO) are presently considered very suitable starting material, showing enhanced chemical...

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