scholarly journals Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

2014 ◽  
Vol 10 ◽  
pp. 1896-1905 ◽  
Author(s):  
Alexander F Khlebnikov ◽  
Mikhail S Novikov ◽  
Yelizaveta G Gorbunova ◽  
Ekaterina E Galenko ◽  
Kirill I Mikhailov ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Experimental Studies ◽  
Diazo Compounds ◽  
Stationary Points ◽  
Reaction Intermediates ◽  
Reaction Conditions ◽  
Open Chain ◽  
Isoxazole Ring ◽  
Diazo Esters ◽  
Probable Reaction

Theoretical and experimental studies of the reaction of isoxazoles with diazo compounds show that the formation of 2H-1,3-oxazines proceeds via the formation of (3Z)-1-oxa-5-azahexa-1,3,5-trienes which undergo a 6π-cyclization. The stationary points corresponding to the probable reaction intermediates, isoxazolium N-ylides, were located by DFT calculations at the B3LYP/6-31G(d) level only for derivatives without a substituent in position 3 of the isoxazole ring. These isoxazolium N-ylides are thermodynamically and kinetically very unstable. According to the calculations and experimental results 2H-1,3-oxazines are usually more thermodynamically stable than the corresponding open-chain isomers, (3Z)-1-oxa-5-azahexa-1,3,5-trienes. The exception are oxaazahexatrienes derived from 5-alkoxyisoxazoles, which are thermodynamically more stable than the corresponding 2H-1,3-oxazines. Therefore, the reaction of diazo esters with 5-alkoxyisoxazoles is a good approach to 1,4-di(alkoxycarbonyl)-2-azabuta-1,3-dienes. The reaction conditions for the preparation of aryl- and halogen-substituted 2H-1,3-oxazines and 1,4-di(alkoxycarbonyl)-2-azabuta-1,3-dienes from isoxazoles were investigated.

DFT Study and Synthesis of Novel Bioactive Bispyrazole Using Mg/AlLDH as a Solid Base Catalyst

2020 ◽  
Vol 14 ◽  
Author(s):  
Soufiane Akhramez ◽  
Youness Achour ◽  
Mustapha Diba ◽  
Lahoucine Bahsis ◽  
Hajiba Ouchetto ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Experimental Finding ◽  
Biological Activities ◽  
Condensation Reaction ◽  
Aromatic Aldehydes ◽  
Mechanistic Study ◽  
Knoevenagel Reaction ◽  
Solid Base ◽  
Reaction Conditions ◽  
Aryl Aldehyde

Background: In this study, an efficient synthesis of novel bispyrazole heterocyclic molecules by condensation of substituted aromatic aldehydes with 1,3-diketo-N-phenylpyrazole by using Mg/Al-LDH as heterogeneous catalyst is reported. The attractive features of this protocol are as follows: mild reaction conditions, good yields and easiness of the catalyst separation from the reaction mixture. Further, a mechanistic study has been performed by using DFT calculations to explain the observed selectivity of the condensation reaction between aryl aldehyde and 1,3-diketo-N-phenylpyrazole via Knoevenagel reaction. The local electrophilicity/ nucleophilicity that allows explaining correctly the experimental finding. Methods: The bispyrazole derivatives 3a-m were prepared by condensation reaction of substituted aromatic aldehydes with 1,3-diketo-Nphenylpyrazole by using Mg/Al-LDH as heterogeneous catalyst under THF solvent at the refluxing temperature. Objective: To synthesize a novel bispyrazole heterocyclic molecule may be have important biological activities and thus can be good candidates for pharmaceutical applications. Results: This protocol describes the Synthesis of Bioactive Compounds under mild reaction conditions, good yields and easiness of the catalyst separation from the reaction mixture. Further, a mechanistic study has been performed by using DFT calculations to explain the observed selectivity of the condensation reaction between aryl aldehyde and 1,3-diketo-N-phenylpyrazole via Knoevenagel reaction. The local electrophilicity/ nucleophilicity that allows explaining correctly the experimental finding. Conclusion: In summary, the pharmacologically interesting bis-pyrazole derivatives have been synthesized through Mg/Al-LDH as a solid base catalyst, in THF as solvent. Thus, the synthesized bioactive compounds containing the pyrazole ring may be have important biological activities and thus can be good candidates for pharmaceutical applications. Therefore, the catalyst Mg/Al-LDH showed high catalytic activity. Besides, a series of bispyrazole molecules were synthesized with a good yield and easy separation of the catalyst by simple filtration. Moreover, DFT calculations and reactivity indexes are used to explain the selectivity of the condensation reaction between aryl benzaldehyde and 1,3-diketo-Nphenylpyrazole via Knoevenagel reaction, and the results are in good agreement with the experimental finding.

Synthesis of pyrazolo[1,5-c]quinazoline derivatives through the copper-catalyzed domino reaction of o-alkenyl aromatic isocyanides with diazo compounds

2020 ◽  
Vol 56 (55) ◽  
pp. 7665-7668 ◽  
Author(s):  
Lu Liu ◽  
Lei Li ◽  
Shukuan Mao ◽  
Xin Wang ◽  
Ming-Dong Zhou ◽  
...  
Keyword(s):  
Diazo Compounds ◽  
Domino Reaction ◽  
Reaction Conditions ◽  
One Pot ◽  
One Pot Synthesis ◽  
Quinazoline Derivatives

Various o-alkenyl aromatic isocyanides were prepared from readily available reactants for their double annulation with diazo compounds for a one-pot synthesis of pyrazolo[1,5-c]quinazolines under mild reaction conditions.

In situ loading of well-dispersed silver nanoparticles on nanocrystalline magnesium oxide for real-time monitoring of catalytic reactions by surface enhanced Raman spectroscopy

Nanoscale ◽  
2015 ◽  
Vol 7 (40) ◽  
pp. 16952-16959 ◽  
Author(s):  
Kaige Zhang ◽  
Gongke Li ◽  
Yuling Hu
Keyword(s):  
Raman Spectroscopy ◽  
Surface Enhanced Raman Spectroscopy ◽  
Catalytic Reactions ◽  
Reaction Intermediates ◽  
Reaction Conditions ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Nanocrystalline Magnesium Oxide ◽  
Insight Into

The surface-enhanced Raman spectroscopy (SERS) technique is of great importance for insight into the transient reaction intermediates and mechanistic pathways involved in heterogeneously catalyzed chemical reactions under actual reaction conditions, especially in water.

Nitroxides as reaction intermediates

1982 ◽  
Vol 60 (12) ◽  
pp. 1414-1420 ◽  
Author(s):  
Hans Gunter Aurich
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Isopropyl Alcohol ◽  
High Reactivity ◽  
Reaction Intermediates ◽  
Reaction Products ◽  
Nitronyl Nitroxide ◽  
Reaction Conditions ◽  
Spin Resonance ◽  
Secondary Reactions

Vinyl nitroxides 4 are obtained by oxidation of the nitrones 3, as was shown by esr studies and by identification of the reaction products. The formation of 4d–f is even observed in oxidation of the hydroxylamines 1d–f, nitroxides 2d–f and nitrones 3d–f being the intermediates. The high reactivity of the vinyl nitroxides 4 at their β-position is illustrated by the reactions of 4a with various compounds affording the nitroxides 7–10, respectively. Compound 4c reacts with its precursor 3c to give 11, 12, or 13, depending on the reaction conditions. From oxidation of 3a, c, and e the dimerization products 5a, c, and e, respectively, could be isolated. Whereas further oxidation of 5d yields 6d, the acyl nitroxides 14a and c are formed in the oxidation of 5a and c, respectively.The formation of quinone 23 in the reaction of 2-methyl-2-nitrosopropane with potassium tert-butoxide in isopropyl alcohol in the presence of oxygen is discussed. The nitroxide 20 has been detected in the reaction mixture. Imines 24 react with nitrosobenzene giving nitroxides 26. These are further oxidized by nitrosobenzene to afford nitrones 27. Whereas 27a and b could be isolated, 27c and d undergo further reaction yielding the diimines 30c and d along with dinitrone 29.The formation and reactions of imino nitroxides 31 and of the nitronyl nitroxide 41 are discussed. Electron spin resonance studies revealed the high reactivity of the imidazolyl-1,3-dioxides 46 and the imidazolyl-1-oxides 50, which easily form radicals 47–49 and 51, respectively, which are derived from secondary reactions.

Anionic ribose related species explored through PES experiments, DFT calculations, and through comparison with anionic fructose species

2017 ◽  
Vol 19 (42) ◽  
pp. 28950-28962 ◽  
Author(s):  
Zhen Zeng ◽  
Elliot R. Bernstein
Keyword(s):  
Dft Calculations ◽  
Related Species ◽  
Open Chain

Generation of (ribose-H)− is dependent on deposition substrates, while generation of two types of (ribose-H2O)− isomers (open chain) is not.

Tropylium Salt Promoted Hydroboration Reactions: Mechanistic Insights via Experimental and Computational Studies

2021 ◽  
Author(s):  
Nhan Nu Hong Ton ◽  
Binh Khanh Mai ◽  
Thanh Vinh Nguyen
Keyword(s):  
Dft Calculations ◽  
Lewis Acids ◽  
Experimental Studies ◽  
Cross Coupling ◽  
Computational Studies ◽  
Metal Free ◽  
Hydride Abstraction ◽  
Novel Method ◽  
Tropylium Salts

Abstract: Hydroboration reaction of alkynes is one of the most synthetically powerful tools to access organoboron compounds, versatile precursors for cross coupling chemistry. This type of reaction has traditionally been mediated by transition metal or main group catalysts. Herein, we report a novel method using tropylium salts, typically known as organic oxidants and Lewis acids, to efficiently promote the hydroboration reaction of alkynes. A broad range of vinylboranes can be easily accessed via this metal-free protocol. Similar hydroboration reactions of alkenes and epoxides can also be efficiently catalyzed by the same tropylium catalysts. Experimental studies and DFT calculations suggested that the reaction follows an uncommon mechanistic paradigm, which is triggered by a hydride abstraction of pinacolborane with tropylium ion. This is followed by a series of <i>in situ</i> counterion-activated substituent exchanges to generate boron intermediates that promote the hydroboration reaction.

scholarly journals Taking the next step toward inert Mn2+ complexes of open-chain ligands: the case of the rigid PhDTA ligand

2018 ◽  
Vol 42 (10) ◽  
pp. 8001-8011 ◽  
Author(s):  
Kristof Pota ◽  
Zoltán Garda ◽  
Ferenc Krisztián Kálmán ◽  
José Luis Barriada ◽  
David Esteban-Gómez ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Electrochemical Properties ◽  
Dissociation Kinetics ◽  
Open Chain ◽  
Equilibrium Dissociation

Equilibrium, dissociation kinetics, relaxometric and electrochemical properties of the [Mn(PhDTA)]2− complex were investigated and the structure of the [Mn(PhDTA)]2− complex was studied by using DFT calculations.

scholarly journals Oxidant speciation and anionic ligand effects in the gold-catalyzed oxidative coupling of arenes and alkynes

2019 ◽  
Vol 10 (36) ◽  
pp. 8411-8420 ◽  
Author(s):  
Manuel Hofer ◽  
Teresa de Haro ◽  
Enrique Gómez-Bengoa ◽  
Alexandre Genoux ◽  
Cristina Nevado
Keyword(s):  
Dft Calculations ◽  
Oxidative Coupling ◽  
Cross Coupling ◽  
Reaction Intermediates ◽  
Ligand Effects ◽  
Anionic Ligand

The mechanism of the gold-catalyzed oxidative cross-coupling of arenes and alkynes has been studied in detail combining stoichiometric experiments with putative reaction intermediates and DFT calculations.

A chiral Brønsted acid-catalyzed highly enantioselective Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines

2018 ◽  
Vol 54 (28) ◽  
pp. 3516-3519 ◽  
Author(s):  
Rajshekhar A. Unhale ◽  
Milon M. Sadhu ◽  
Sumit K. Ray ◽  
Rayhan G. Biswas ◽  
Vinod K. Singh
Keyword(s):  
Phosphoric Acid ◽  
Reaction Conditions ◽  
Type Reaction ◽  
Chiral Phosphoric Acid ◽  
Brönsted Acid ◽  
Diazo Esters ◽  
Reaction Proceeds ◽  
Acid Catalyzed ◽  
Chiral Bronsted Acid

A chiral phosphoric acid-catalyzed asymmetric Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines, derived from 3-aryl-3-hydroxyisoindolinones has been demonstrated. The reaction proceeds smoothly under mild reaction conditions.

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