A photoredox catalyzed iminyl radical-triggered C–C bond cleavage/addition/Kornblum oxidation cascade of oxime esters and styrenes: synthesis of ketonitriles

2018 ◽  
Vol 54 (86) ◽  
pp. 12262-12265 ◽  
Author(s):  
Bin-Qing He ◽  
Xiao-Ye Yu ◽  
Peng-Zi Wang ◽  
Jia-Rong Chen ◽  
Wen-Jing Xiao
Keyword(s):  
Bond Cleavage ◽  
Kornblum Oxidation ◽  
First Time

A photoredox-catalyzed iminyl radical-triggered C–C bond cleavage/addition/Kornblum oxidation cascade of cycloketone oxime esters and styrenes in DMSO is described for the first time.

scholarly journals Exchange Speed of Four-Component Nanorotors Correlates with Hammett Substituent Constants

Chemistry ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 116-125
Author(s):  
Yi-Fan Li ◽  
Amit Ghosh ◽  
Pronay Kumar Biswas ◽  
Suchismita Saha ◽  
Michael Schmittel
Keyword(s):  
Linear Correlation ◽  
Bond Cleavage ◽  
Head Group ◽  
Ligand Interaction ◽  
Exchange Frequency ◽  
Rate Determining Step ◽  
Head Groups ◽  
Substituent Constants ◽  
First Time ◽  
Determining Factor

Three distinct four-component supramolecular nanorotors were prepared, using, for the first time, bipyridine instead of phenanthroline stations in the stator. Following our established self-sorting protocol to multicomponent nanodevices, the nanorotors were self-assembled by mixing the stator, rotators with various pyridine head groups, copper(I) ions and 1,4-diazabicyclo[2.2.2]octane (DABCO). Whereas the exchange of a phenanthroline vs. a bipyridine station did not entail significant changes in the rotational exchange frequency, the para-substituents at the pyridine head group of the rotator had drastic consequences on the speed: 4-OMe (k298 = 35 kHz), 4-H (k298 = 77 kHz) and 4-NO2 (k298 = 843 kHz). The exchange frequency (log k) showed an excellent linear correlation with both the Hammett substituent constants and log K of the copper(I)–ligand interaction, proving that rotator–copper(I) bond cleavage is the key determining factor in the rate-determining step.

A highly sensitive naked-eye fluorescent probe for trace hydrazine based on ‘C-CN’ bond cleavage

The Analyst ◽  
2018 ◽  
Vol 143 (18) ◽  
pp. 4354-4358 ◽  
Author(s):  
Hai Xu ◽  
Zhen Huang ◽  
Yaqian Li ◽  
Biao Gu ◽  
Zile Zhou ◽  
...  
Keyword(s):  
Detection Limit ◽  
Fluorescent Probe ◽  
Water Samples ◽  
Bond Cleavage ◽  
Eye Detection ◽  
Naked Eye ◽  
Real Water Samples ◽  
Highly Sensitive ◽  
First Time ◽  
Naked Eye Detection

The ‘C–CN’ bond cleavage was applied to the recognition of N2H4 for the first time; the obvious change in color could be used for “naked-eye” detection; the corresponding detection limit was found to be 5.81 × 10−8 M (1.65 ppb); the probe could be applied for N2H4 detection in real water samples.

scholarly journals The difference in stability between 5′R and 5′S diastereomers of 5′,8-cyclopurine-2′-deoxynucleosides. DFT study in gaseous and aqueous phase

2010 ◽  
Vol 8 (1) ◽  
pp. 134-141 ◽  
Author(s):  
Boleslaw Karwowski
Keyword(s):  
Density Functional ◽  
Bond Cleavage ◽  
Basis Set ◽  
Small Range ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Formic Acid Hydrolysis ◽  
The Difference ◽  
The Stability ◽  
First Time

AbstractOxidatively generated damage to DNA frequently appears in the human genome as an effect of aerobic metabolism or as the result of exposure to exogenous oxidizing agents. Due to these facts it has been decided to calculate the stability of 5′,8-cyclo-2′-deoxyadenosine/guanosine (cdA, cdG) in their 5′R and 5′S diastereomeric forms. For all points of quantum mechanics studies presented, the density functional theory (DFT) with B3LYP parameters on 6-311++G** basis set level was used. The calculations showed a significant negative enthalpy for glycosidic bond cleavage reaction for cationic forms and slightly negative for neutral ones. The preliminary study of the discussed process has shown the nature of stepwise nucleophilic substitution DN*AD type mechanism. Surprisingly, the different values in free energy, between short-lived oxacarbenium ion intermediates, have been found to lie over a relatively small range, around 1 and 2.8 kcal mol−1. For anions, the decomposition enthalpies were found as positive in aqueous phases. These theoretical results are supported by the formic acid hydrolysis experiments of both diastereomers of cdA, for the first time. (5′S)cdA exhibited higher stability than (5′R)cdA.

Sterically-controlled intermolecular Friedel–Crafts acylation with twisted amides via selective N–C cleavage under mild conditions

2016 ◽  
Vol 52 (41) ◽  
pp. 6841-6844 ◽  
Author(s):  
Yongmei Liu ◽  
Guangrong Meng ◽  
Ruzhang Liu ◽  
Michal Szostak
Keyword(s):  
Bond Cleavage ◽  
Mild Conditions ◽  
First Time

Highly chemoselective Friedel–Crafts acylation of arenes with twisted amides by N–C bond cleavage is reported for the first time.

scholarly journals Selective Manganese-Catalyzed Dimerization and Cross-Coupling of Terminal Alkynes

2021 ◽  
Author(s):  
Stefan Weber ◽  
Luis F. Veiros ◽  
Karl Kirchner
Keyword(s):  
Dft Calculations ◽  
Precious Metal ◽  
Bond Cleavage ◽  
Cross Coupling ◽  
Metal Catalyst ◽  
Catalyst Loading ◽  
Terminal Alkynes ◽  
Migratory Insertion ◽  
Earth Abundant ◽  
First Time

<div>For the first time, an efficient manganese-catalyzed dimerization of terminal alkynes to afford 1,3-enynes is described. This reaction is atom economic, implementing an inexpensive, earth abundant non-precious metal catalyst. The pre-catalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which undergoes rapid C-H bond cleavage of the alkyne forming an active Mn(I) acetylide catalyst [Mn(dippe)(CO)2(C≡CPh)(η2-HC≡CPh)] together with liberated butanal. A range of aromatic and aliphatic terminal alkynes were efficiently and selectively converted into head-to-head Z-1,3-enynes and head-to-tail gem-1,3-enynes, respectively, in good to excellent yields. Moreover, cross-coupling of aromatic and aliphatic alkynes yields selectively head-to-tail gem-1,3-enynes. In all cases, the reactions were performed at 70 °C with a catalyst loading of 1-2 mol %. A mechanism based on DFT calculations is presented.</div><div><br></div>

scholarly journals Microbial Cleavage of C‒F Bonds in Per- and Polyfluoroalkyl Substances via Dehalorespiration

2019 ◽  
Author(s):  
Yaochun Yu ◽  
Kunyang Zhang ◽  
Zhong Li ◽  
Changxu Ren ◽  
Jinyong Liu ◽  
...  
Keyword(s):  
Microbial Community ◽  
Dissociation Energy ◽  
Environmental Fate ◽  
Bond Cleavage ◽  
Convincing Evidence ◽  
Enoic Acid ◽  
Scientific Question ◽  
Fundamental Knowledge ◽  
Polyfluoroalkyl Substances ◽  
First Time

Regarding the emerging concerns of the widely occurred and environmentally persistent per- and polyfluoroalkyl substances (PFASs), one intriguing and unsolved scientific question for environmental microbiologists, chemists, and engineers is that whether microbial reductive defluorination of perfluorinated compounds exist in nature. Due to the strong dissociation energy of carbon‒fluorine (C‒F) bonds in PFASs, no convincing evidence for biological cleavage of C‒F bonds from > C<sub>2</sub> perfluorinated structures has ever been reported. We for the first time show C‒F bond cleavage via reductive defluorination by an organohalide-respiring microbial community for two PFASs, perfluoro(4-methylpent-2-enoic acid) and 4,5,5,5-tetrafluoro-4-(trifluoromethyl)-2-pentenoic acid. Comprehensive biotransformation pathways are further elucidated. This study brings valuable fundamental knowledge of microbial dehalorespiration, which opens avenues for the future exploration of PFAS environmental fate and bioremediation strategies.

scholarly journals Selective Manganese-Catalyzed Dimerization and Cross-Coupling of Terminal Alkynes

2021 ◽  
Author(s):  
Stefan Weber ◽  
Luis F. Veiros ◽  
Karl Kirchner
Keyword(s):  
Dft Calculations ◽  
Precious Metal ◽  
Bond Cleavage ◽  
Cross Coupling ◽  
Metal Catalyst ◽  
Catalyst Loading ◽  
Terminal Alkynes ◽  
Migratory Insertion ◽  
Earth Abundant ◽  
First Time

<div>For the first time, an efficient manganese-catalyzed dimerization of terminal alkynes to afford 1,3-enynes is described. This reaction is atom economic, implementing an inexpensive, earth abundant non-precious metal catalyst. The pre-catalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic process is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which undergoes rapid C-H bond cleavage of the alkyne forming an active Mn(I) acetylide catalyst [Mn(dippe)(CO)2(C≡CPh)(η2-HC≡CPh)] together with liberated butanal. A range of aromatic and aliphatic terminal alkynes were efficiently and selectively converted into head-to-head Z-1,3-enynes and head-to-tail gem-1,3-enynes, respectively, in good to excellent yields. Moreover, cross-coupling of aromatic and aliphatic alkynes yields selectively head-to-tail gem-1,3-enynes. In all cases, the reactions were performed at 70 °C with a catalyst loading of 1-2 mol %. A mechanism based on DFT calculations is presented.</div><div><br></div>

Microbial Cleavage of C‒F Bonds in Per- and Polyfluoroalkyl Substances via Dehalorespiration

2019 ◽  
Author(s):  
Yaochun Yu ◽  
Kunyang Zhang ◽  
Zhong Li ◽  
Changxu Ren ◽  
Jinyong Liu ◽  
...  
Keyword(s):  
Microbial Community ◽  
Dissociation Energy ◽  
Environmental Fate ◽  
Bond Cleavage ◽  
Convincing Evidence ◽  
Enoic Acid ◽  
Scientific Question ◽  
Fundamental Knowledge ◽  
Polyfluoroalkyl Substances ◽  
First Time

Regarding the emerging concerns of the widely occurred and environmentally persistent per- and polyfluoroalkyl substances (PFASs), one intriguing and unsolved scientific question for environmental microbiologists, chemists, and engineers is that whether microbial reductive defluorination of perfluorinated compounds exist in nature. Due to the strong dissociation energy of carbon‒fluorine (C‒F) bonds in PFASs, no convincing evidence for biological cleavage of C‒F bonds from > C<sub>2</sub> perfluorinated structures has ever been reported. We for the first time show C‒F bond cleavage via reductive defluorination by an organohalide-respiring microbial community for two PFASs, perfluoro(4-methylpent-2-enoic acid) and 4,5,5,5-tetrafluoro-4-(trifluoromethyl)-2-pentenoic acid. Comprehensive biotransformation pathways are further elucidated. This study brings valuable fundamental knowledge of microbial dehalorespiration, which opens avenues for the future exploration of PFAS environmental fate and bioremediation strategies.

scholarly journals Tilting a Ground State Reactivity Landscape by Vibrational Strong Coupling

2018 ◽  
Author(s):  
Anoop Thomas ◽  
Lucas Lethuillier-Karl ◽  
Kalaivanan Nagarajan ◽  
Robrecht M. A. Vergauwe ◽  
Jino George ◽  
...  
Keyword(s):  
Strong Coupling ◽  
Activation Barrier ◽  
Chemical Reactivity ◽  
Bond Cleavage ◽  
Optical Cavity ◽  
Vacuum Field ◽  
Activation Entropy ◽  
Cleavage Sites ◽  
Site Selectivity ◽  
First Time

Site-selectivity is fundamental for steering chemical reactivity towards a given product and various efficient chemical methods have been developed for this purpose. Here we explore a very different approach by using vibrational strong coupling (VSC) between a reactant and the vacuum field of a microfluidic optical cavity. For this purpose, the reactivity of a compound bearing two possible silyl bond cleavage sites, at Si-C and Si-O, was studied as a function of VSC of its various vibrational modes in the dark. The results show that VSC can indeed tilt the reactivity landscape to favor one product over the other. Thermodynamic parameters reveal the presence of a large activation barrier and significant changes to the activation entropy, confirming the modified chemical landscape under strong coupling. This study shows for the first time that VSC can impart site-selectivity for chemical reactions without the need for chemical intervention.

scholarly journals Hydrogenolysis cleavage of Csp2-Csp3 bond over a metal-free NbOPO4 catalyst

2021 ◽  
Author(s):  
Hao Zhou ◽  
Lu Chen ◽  
Yong Guo ◽  
Xiaohui Liu ◽  
Xin-Ping Wu ◽  
...  
Keyword(s):  
Density Functional ◽  
Oxygen Vacancies ◽  
High Selectivity ◽  
Bond Cleavage ◽  
Acid Sites ◽  
Model Compounds ◽  
Functional Theory ◽  
In Situ Drift ◽  
First Time

Ru/NbOx catalysts, which combine the merits of facile hydrogen activation, strong binding to benzene ring and the presence of Brønsted acid sites, were well investigated toward Csp2-Csp3 bond cleavage. Herein, we unlock the ability of bare NbOx catalyst in the dissociation and activation of hydrogen molecule and further hydrogenolysis of the Csp2-Csp3 model compounds including polystyrene (PS). In-situ Drift and density functional theory (DFT) calculations reveal that H2 can be dissociated and surface hydride species can be produced over Nb2O5 through heterolytic and homolytic cleavages of H2. We also find that the existence of surface oxygen vacancies plays a key role in stabilizing hydride species. Further, the NbOPO4 catalyst not only allows the conversion of phenylcyclohexane to monocyclic compounds by cleaving Csp2-Csp3 bond, but also enables the conversion of PS to arenes with a high selectivity. This study provides and proves for the first time, the unique ability of metal oxides (phosphates) in the hydrogenolysis of compounds and plastics containing Csp2-Csp3 bonds.

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