Search results for "EOP"

2020

The course of organic chemical reactions is efficiently modelled through the concepts of “electrophiles” and “nucleophiles” (meaning electron-seeking and nucleus-seeking reactive species). On the one hand, an advanced approach of the correlation of the nucleophilicity parameters N and electrophilicity E has been delivered from the linear free energy relationship log k (20 °C) = s(N + E). On the other hand, the general influence of the solvent mixtures, which are very often employed in preparative synthetic chemistry, has been poorly explored theoretically and experimentally, to date. Herein, we combined experimental and theoretical studies of the solvent influence on pyrrolidine nucleophili…

A Molecular Electron Density Theory Study of the Role of the Copper Metalation of Azomethine Ylides in [3 + 2] Cycloaddition Reactions.

2018

The copper metalation of azomethine ylides (AYs) in [3 + 2] cycloaddition (32CA) reactions with electron-deficient ethylenes has been studied within the Molecular Electron Density Theory (MEDT) at the MPWB1K/6-311G(d,p) level, in order to shed light on the electronic effect of the metalation in the course of the reaction. Analysis of the Conceptual Density Functional Theory reactivity indices indicates that the metalation of AYs markedly enhances the nucleophilicity of these species given the anionic character of the AY framework. These 32CA reactions take place through stepwise mechanisms characterized by the formation of a molecular complex. Both nonmetalated and metalated 32CA reactions …

Understanding the Participation of Fluorinated Azomethine Ylides in Carbenoid-Type [3 + 2] Cycloaddition Reactions with Ynal Systems: A Molecular Ele…

2021

The carbenoid-type (cb-type) 32CA reaction of 1,1-difluoroated azomethine ylide (DFAY) with phenylpropynal has been studied using the molecular electron density theory (MEDT). Electron localization function (ELF) characterizes DFAY as a carbenoid species participating in cb-type 32CA reactions. The supernucleophilic character of DFAY and the strong electrophilic character of the ynal cause this polar 32CA reaction to have an unappreciable barrier; the reaction, which is highly exothermic, presents total chemo- and regioselectivity. ELF topological analysis of the bonding changes along the reaction establishes its non-concerted two-stage one-step mechanism, in which the nucleophilic attack o…

Mononuclear Rearrangement of the Z-Phenylhydrazones of Some 3-Acyl-1,2,4-oxadiazoles: Effect of Substituents on the Nucleophilic Character of the &gt…

2019

The reaction rates for the mononuclear rearrangement of the Z-phenylhydrazones of 3-acyl-1,2,4-oxadiazoles 3a-c into the relevant 2-phenyl-2 H-1,2,3-triazoles (4a-c) have been measured in dioxane/water at different temperatures in a large range of proton concentrations. The occurrence of two different reaction pathways (one uncatalyzed, water assisted, and the other general base catalyzed) has- been observed. The obtained results have been able to furnish information about the effects of the nature of the 3-acyl structure and of the 5-substituents in the 1,2,4-oxadiazole ring on the reactivity of the examined rearrangements: they are well in line with the previsions carried out considering …

Formation of dibutyl carbonate and butylcarbamate via CO2 insertion in titanium(IV) butoxide and reaction with n-butylamine

2016

Abstract The species resulting from insertion of 12CO2 and 13CO2 into titanium(IV) butoxide is for the first time fully characterized by means of infrared and nuclear magnetic resonance spectroscopy. Results show formation of Ti-monobutylcarbonate, that easily undergoes nucleophilic attack by an aliphatic amine. The hydrolysis of the resulting species produces butylcarbamate and dibutylcarbonate as the only main products. Characterization results of the carbonate-like adduct, along with its reactivity with amine molecules open the route to new ways of CO2 utilization as building block for valuable organic compounds.

Regio- and Stereoselective Synthesis of 3-Pyrazolylidene-2-oxindole Compounds by Nucleophilic Vinylic Substitution of (E)-3-(Nitromethylene)indolin-2…

2019

[EN] A highly regio- and stereoselective synthesis of 3-alkylidene-2-oxindoles has been described through a nucleophilic vinylic substitution (SNV) of (E)-3-(nitromethylene)indolin-2-one using pyrazol-3-ones as nucleophiles and Et3N as a base. The reaction affords selectively the Z-isomer when pyrazol-3-ones without substituents at the 4 position are used. While the reaction is E-selective with 4- substituted pyrazolones. The stereoselectivity (up to >20:1) and the yields (up to 98%) are very high under mild reaction conditions.

Arene C−H Activation at Aluminium(I): meta Selectivity Driven by the Electronics of S N Ar Chemistry

2020

The reactivity of the electron-rich anionic Al(I) ('aluminyl') compound K 2 [(NON)Al] 2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di- tert -butyl-9,9-dimethylxanthene) towards mono- and disubstituted arenes is reported. C-H activation chemistry with n -butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer-type transition state. Selectivity is therefore based on similar electronic factors to classical S N Ar chemistry, which implies the destabilization of transition states featuring electron-donating groups in either the ortho or the para positions. In the cases of tolu…

Sequential Nucleophilic−Electrophilic Reactions Selectively Produce Isomerically Pure Nona‐ B ‐Substituted o ‐Carborane Derivatives

2003

Nine equal substituents on the intensively studied o-carborane have been obtained for the first time by a combined nucleophilic-electrophilic reaction sequence. Iodine and methyl groups have been introduced to prove the generality of the method. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Vinyl sulfone building blocks in covalently reversible reactions with thiols

2015

In the present study we use quantum-chemical calculations to investigate how the reactivity of vinyl sulfone-based compounds can be modified from an irreversible to a reversible reaction with thiols. Based on the predictions from theory, an array of nine different vinyl sulfones with systematically varying substitution pattern was synthesized and their crystal structures were determined. Subsequent Hirshfeld surface analyses employing the principle of electrostatic complementarity aid the understanding of the crystal packing of the synthesized compounds. Reactivity studies against the nucleophile 2-phenylethanethiol mirror the properties predicted by the quantum-chemical computations in sol…

Exploratory Synthesis of Low-Silica Nanozeolites through Geopolymer Chemistry

2019

Nanozeolites are of great interest with the premise of their efficiency in traditional applications such as catalysis and separation, as well as their emerging applications including chemical sensors, medicine, and food industry. We report a new geopolymerization route for the synthesis of nanozeolites with different crystal structures by exploring the Na–Al–Si–H2O quaternary phase space under a mild hydrothermal condition. Nanostructured faujasite (FAU), cancrinite (CAN), and sodalite (SOD) zeolites with a crystallite size smaller than 40 nm were successfully produced from our exploration, as well as a submicron-sized Linde-Type A (LTA) zeolite. The transmission electron microscopy and nit…