scholarly journals The stereoselectivities of tributyltin hydride-mediated reductions of 5-bromo-d-glucuronides to l-iduronides are dependent on the anomeric substituent: syntheses and DFT calculations

2016 ◽  
Vol 14 (10) ◽  
pp. 2950-2960 ◽  
Author(s):  
Shifaza Mohamed ◽  
Elizabeth H. Krenske ◽  
Vito Ferro
Keyword(s):  
Dft Calculations ◽  
Transition State ◽  
Tributyltin Hydride ◽  
Gauche Effect

Reduction of a 5-C-bromo-d-glucuronyl β-fluoride with tributyltin hydride gives exclusively the l-ido product. The selectivity is traced to a transition state gauche effect and an Sn–F interaction.

Reactions of an Aluminium(I) Reagent with 1,2-, 1,3- and 1,5-Dienes: Dearomatisation, Reversibility, and a Pericyclic Mechanism

2019 ◽  
Author(s):  
Clare Bakewell ◽  
Martí Garçon ◽  
Richard Y Kong ◽  
Louisa O'Hare ◽  
Andrew J. P. White ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transition State ◽  
Reaction Pathways ◽  
Aromatic Rings ◽  
Aromatic Character ◽  
Pericyclic Reaction

The reactions of an aluminium(I) reagent with a series of 1,2-, 1,3- and 1,5-dienes are reported. In the case of 1,3-dienes the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene containing products. This mechanism has been interrogated by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4+1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4+1) cycloaddition includes dienes that are either in part, or entirely, contained within aromatic rings. In these cases, reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2- or 1,5-dienes complementary reactivity is observed; the orthogonal nature of the C=C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavour a (4+1) cycloaddition. Rather, reaction pathways are determined by an initial (2+1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C π-bond leading to complex organometallic products that incorporate fused hydrocarbon rings.

scholarly journals Theoretical study on pegylation reaction mechanisms of IFN-α-2a, IFN-α-2b and IFN-β-1a

2017 ◽  
Vol 82 (7-8) ◽  
pp. 841-850
Author(s):  
Mohammad Taqavian ◽  
Daryoush Abedi ◽  
Fatemeh Zigheimat ◽  
Leila Zeidabadinejad
Keyword(s):  
Polyethylene Glycol ◽  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transition State ◽  
Reaction Mechanisms ◽  
Theoretical Study ◽  
Computational Study ◽  
Single Transition ◽  
Experimental Works ◽  
Ab Initio And Dft

Ab initio and DFT calculations have been carried out to study the reaction mechanism between interferons (IFNs) ?-2a, ?-2b and ?-1a and polyethylene glycol (PEG) group. The calculations show that the mechanisms are concerted, in agreement with the results of experimental works. However, although it appears that there is one single transition state, the characteristics of its structure reveal a very synchronous reaction mechanism. The reactions are clearly exothermic and as well have feasible activation energies. Our computational study shows that the lowest transition state energies are related to Lys 134, His 34 and Met 1 of IFN-?-2a, IFN-?-2b and IFN-?-1a, respectively.

scholarly journals Ligand-Controlled Regiodivergence in Nickel-Catalyzed Hydroarylation and Hydroalkenylation of Alkenyl Carboxylic Acids

2020 ◽  
Author(s):  
Zi-Qi Li ◽  
Yue Fu ◽  
Ruohan Deng ◽  
Van Tran ◽  
Yang Gao ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Transition State ◽  
Carboxylic Acids ◽  
Alkyl Group ◽  
Steric Effects ◽  
High Yield ◽  
Mechanistic Studies ◽  
Ligand Environment ◽  
Ligand Free ◽  
Electronic And Steric Effects

<div>A nickel-catalyzed regiodivergent hydroarylation and hydroalkenylation of unactivated alkenyl carboxylic acids is reported, whereby the ligand environment around the metal center dictates the regiochemical outcome. Markovnikov hydrofunctionalization products are obtained under mild ligand-free conditions, with up to 99% yield and >20:1 selectivity. Alternatively, anti-Markovnikov products can be accessed with a novel 4,4-disubstituted Pyrox ligand in excellent yield and >20:1 selectivity. Both electronic and steric effects on the ligand contribute to the high yield and selectivity. Mechanistic studies suggest a change in the turnover-limiting and selectivity-determining step induced by the optimal ligand. DFT calculations reveal that in the anti-Markovnikov pathway, repulsion between the ligand and the alkyl group is minimized (by virtue of it being 1° versus 2°) in the rate- and regioselectivity-determining transmetalation transition state. <br></div>

Reactions of an Aluminium(I) Reagent with 1,2-, 1,3- and 1,5-Dienes: Dearomatisation, Reversibility, and a Pericyclic Mechanism

2019 ◽  
Author(s):  
Clare Bakewell ◽  
Martí Garçon ◽  
Richard Y Kong ◽  
Louisa O'Hare ◽  
Andrew J. P. White ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transition State ◽  
Reaction Pathways ◽  
Aromatic Rings ◽  
Aromatic Character ◽  
Pericyclic Reaction

The reactions of an aluminium(I) reagent with a series of 1,2-, 1,3- and 1,5-dienes are reported. In the case of 1,3-dienes the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene containing products. This mechanism has been interrogated by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4+1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4+1) cycloaddition includes dienes that are either in part, or entirely, contained within aromatic rings. In these cases, reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2- or 1,5-dienes complementary reactivity is observed; the orthogonal nature of the C=C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavour a (4+1) cycloaddition. Rather, reaction pathways are determined by an initial (2+1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C π-bond leading to complex organometallic products that incorporate fused hydrocarbon rings.

Direct Ortho-Metallation of Aryl Substituted Heteroaromatic Ligands with TiCl 4 and ZrCl 4 - An Experimental and DFT Study with 2-Phenyl Indole as the Ligand.

2019 ◽  
Author(s):  
Gregory Arzoumanidis ◽  
Ernest Chamot
Keyword(s):  
Dft Calculations ◽  
Transition State ◽  
Photoelectron Spectroscopy ◽  
Analytical Data ◽  
Phenyl Group ◽  
Building Blocks ◽  
One Pot ◽  
Polymerization Catalysis ◽  
Cyclometallated Complexes ◽  
C Nmr

TiCl 4 and ZrCl 4 each react with aryl substituted heteroaromatic ligands such as 2-Phenyl-1H-indole, to thermally undergo one-pot direct orthometallations, and yield new types of cyclometallated complexes. TiCl 4 coordinates at ambient temperature to form the indole complex ( 1 ), which undergoes isomerization to the indolenine ( 2 ). DFT calculations indicate that complex ( 2 ) is more stable than ( 1 ) by 6.4 kcal/mol. Upon warming to about 105°C, extrusion of HCl takes place with simultaneous orthometallation ( 3 ), yielding a metallacyclic complex ( 4 ). The mechanism of the orthometallation has been investigated by DFT, and the transition state c onfir med by IRC. At the elevated temperature the transition state ( 3 ) involves the synchronous transformation of four atoms, Ti, ortho C, H, and the apical Cl. The ortho C of the phenyl group acquires a partial positive charge through conjugation, forming a (C-H)δ + ...Clδ - interaction, with a simultaneous elongation and breaking of the Ti-Cl bond, resulting in the formation of a Ti-C bond. The latter bond is created at the same time a Ti-Cl bond is breaking, and an HCl is being formed, as illustrated in transition state ( 3 ). This HCl is retained in the crystal structure of the final product ( 4 ), by electrostatic interaction with one of the chloride ligands. The reaction sequence may be repeated with ZrCl 4 in place of TiCl 4 . Complex ( 4 ) has been isolated and characterized by solid state 13 C NMR CPMAS/DDMAS spectra, X-ray photoelectron spectroscopy (XPS), infrared and analytical data. The intermediate structures ( 1 through 4 ), as well as the sequence of ligand transformations to produce the ortho-metallated complex are supported by DFT calculations. The new cyclometallated complexes are thermally stable, unlike several other complexes featuring a Ti-C bond. They may have important applications, such as in α-olefin polymerization catalysis, and as building blocks in metalodrugs for cancer therapy.<br>

scholarly journals An aniline dication-like transition state in the Bamberger rearrangement

2013 ◽  
Vol 9 ◽  
pp. 1073-1082 ◽  
Author(s):  
Shinichi Yamabe ◽  
Guixiang Zeng ◽  
Wei Guan ◽  
Shigeyoshi Sakaki
Keyword(s):  
Activation Energy ◽  
Dft Calculations ◽  
Transition State ◽  
Water Cluster ◽  
Transition States ◽  
Activation Energies ◽  
Nitrenium Ion ◽  
Proton Transfers ◽  
First Time

A Bamberger rearrangement of N-phenylhydroxylamine, Ph–N(OH)H, to p-aminophenol was investigated by DFT calculations for the first time. The nitrenium ion, C6H5–NH+, suggested and seemingly established as an intermediate was calculated to be absent owing to the high nucleophilicity of the water cluster around it. First, a reaction of the monoprotonated system, Ph–N(OH)H + H3O+(H2O) n (n = 4 and 14) was examined. However, the rate-determining transition states involving proton transfers were calculated to have much larger activation energies than the experimental one. Second, a reaction of the diprotonated system, Ph–N(OH)H + (H3O+)2(H2O)13, was traced. An activation energy similar to the experimental one was obtained. A new mechanism of the rearrangement including the aniline dication-like transition state was proposed.

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