Search results for "Electrophile"
showing 10 items of 258 documents
Theoretical study on the molecular mechanism of the [5 + 2] vs. [4 + 2] cyclization mediated by Lewis acid in the quinone system
2013
[EN] The thermal and Lewis acid (LA) catalyzed cyclizations of quinone 1 involved in the synthesis of Colombiasin A and Elipsaterosin B have been theoretically studied using DFT methods at the B3LYP/6-311G(d,p) computational level. B3LYP calculations suggest that the formal endo [4 + 2] cycloadduct allowing the synthesis of Colombiasin A is preferentially formed under thermal conditions, while in the presence of the BF3 LA catalyst the formal [5 + 2] cycloadduct is seen, allowing the synthesis of Elipsaterosin B. The BF3 LA catalyst not only accelerates the nucleophilic attack on the C2 carbon of the quinone framework through a more polar C-C bond formation, but also provokes a different el…
Understanding the regioselectivity in hetero Diels–Alder reactions. An ELF analysis of the reaction between nitrosoethylene and 1-vinylpyrrolidine
2013
[EN] The regioselectivity in the hetero Diels-Alder reaction between nitrosoethylene 1 and 1-vinylpyrrolidine 2 has been studied by a comparative ELF bonding analysis along the IRC of the endo/ortho and endo/meta regioisomeric channels at the B3LYP/6-31G*. level. Along the most favorable endo/ortho regioisomeric channel, the C-C sigma bond is first formed by coupling of two pseudoradical centers located at the most electrophilic carbon of 1 and the most nucleophilic center of 2. Formation of these relevant pseudoradical centers, which depend on the total charge transfer process along the polar reaction, and not on the approach mode of each reagent, is well characterized by analysis of the a…
Towards an intrinsic nucleofugality scale: the leaving group (lg) ability in ch(3)lg model system
2006
Abstract For an important class of organic reactions in which a fragment of the reactants, the leaving group (LG) or nucleofuge (Z), is detached of the substrate bearing the bonding electron pair, the global electrophilicity index of the CH3LG system is proposed as a reliable descriptor of the intrinsic nucleofugality of the LG. The model is illustrated by ranking within a unique relative scale, the LG ability of 28 functional groups commonly involved in substitution and elimination reactions in organic chemistry.
Chapter 9 The electrophilicity index in organic chemistry
2007
Abstract We review in this chapter the applications of theoretical scales of global and local electrophilicity to rationalize the reactivity and selectivity for a significant number of reactions in organic chemistry. The model is based on the global electrophilicity index, formerly introduced by Maynard et al. and further formalized by Parr et al. The global electrophilicity index categorizes, within a unique absolute scale, the propensity of electron acceptors to acquire additional electronic charge from the environment. The local extension of this index provides useful information about the active sites of electrophiles, thereby allowing the characterization of the intramolecular selectiv…
ChemInform Abstract: Electrophilic Substitution and Cyclization of 2,2′-Bis(N-methylindolyl) : A Simple Access to Potential Protein Kinase C Inhibito…
2010
A strategy is described for the synthesis of functionalized and cyclized 2,2′-bisindolyl derivatives related to several basic systems of natural products. The starting 2,2′-bis(N-methylindolyl) (8) reacts with a variety of electrophiles and electrophilic dienophiles to furnish the novel, functionalized and cyclized bisindolyl derivatives 9–16. In addition, some reactivity and structural aspects are discussed; an X-ray crystallographic analysis of the 2,2′-bisindolyl 8 provided valuable information for the conformational analyses.
First Reactions of 2,2′-Bisindolyls with Electrophilic Azo Compounds and Diethyl Mesoxalate
1992
Conformations and some electronic properties of the 2,2′-bisindolyls 6 were calculated for the prediction of probable Diels-Alder reactivity, in analogy to previous work on 2-vinylindoles. First reactions with dienophiles revealed that compounds 6 did not participate in [4 + 2]cycloadditions but rather underwent simple electrophilic substitutions at the enamine function with, above all, some heterodienophiles. Erste Reaktionen von 2,2′-Bisindolylen mit elektrophilen Azoverbindungen und Diethylmesoxalat Zur Vorhersage moglicher Diels-Alder-Reaktionen an 2,2′-Bisindolylen 6 werden Berechnungen zur Konformation und uber elektronische Eigenschaften durchgefuhrt. Die erstmals durchgefuhrten Reak…
Asymmetric Homoaldol Reactions with Cyclohex-2-enylN,N-Diisopropylcarbamate: Kinetic Resolution, Elucidation of the Stereochemical Course and Applica…
2007
Enantio-enriched cyclohex-2-enyl N,N-diisopropylcarbamate (5) is stereospecifically deprotonated by sec-butyllithium/(–)-sparteine (9) to form the configurationally stable lithium complex 7·9. A kinetic resolution of rac-5 by n-butyllithium/(–)-sparteine (9) yielded (R)-5 with up to 99 % ee. Electrophilic substitution with tin electrophiles proceeds in a anti-SE′ fashion as shown by chemical correlations. The synthesized allylstannanes 10 undergo a highly stereospecific TiCl4-mediated homoaldol reaction with various aldehydes, yielding syn-configured homoaldol products 12. These were transferred into all-cis-configured hexahydroisobenzofuran-4(1H)-ones 22 by BF3·OEt2-mediated reactions with…
Oxidative dehydrogenation of ethane on diluted or promoted nickel oxide catalysts: Influence of the promoter/diluter
2020
Ti- and Nb- containing NiO catalysts have been synthesized by two different preparation methods: i) by precipitation (Me-Ni-O oxides, Me = Nb or Ti), in order to prepare promoted NiO catalysts; and ii) by wet impregnation on TiO or NbO supports, in order to prepare diluted/supported NiO catalysts. The catalysts have been also characterized and tested in the oxidative dehydrogenation of ethane. The catalytic performance of Ti- and Nb-promoted catalysts strongly depends on the composition, although in both cases the optimal one is found at similar Ti or Nb loadings (ca. 90 wt% NiO), showing similar ethylene selectivity in the ODH of ethane (ca. 90% at 10–20% ethane conversion). However, in th…
A dft analysis of the participation of zwitterionic tacs in polar [3+2] cycloaddition reactions
2014
A set of seven non-substituted tri-atom-components (TACs) participating in [3+2] cycloaddition (32CA) reactions has been studied using the reactivity indices defined within the conceptual DFT at the B3LYP/6-31G(d) level of theory. This series of TACs shows a zwitterionic structure and low reactivity towards ethylene. The general characteristic of these TACs is their high nucleophilic and a low electrophilic behaviour. Activation energies computed at the MPWB1K/6-311G(d) level in dichloromethane point to that non-substituted TACs react quickly toward dicyanoethylene showing their ability to react towards electron-deficient ethylenes. However, when the TACs are electrophilically activated by …
The carbenoid-type reactivity of simplest nitrile imine from a molecular electron density theory perspective
2019
Abstract The [3 + 2] cycloaddition (32CA) reactions of the simplest nitrile imine with ethylene and electrophilic dicyanoethylene have been studied within the Molecular Electron Density Theory (MEDT) with the aim of characterising its reactivity. Topological analysis of the electron localisation function of NI shows that it has a carbenoid structure. The activation energy of the 32CA reaction of the simplest nitrile imine with dicyanoethylene is 5.6 kcal mol−1 lower than that involving ethylene, in agreement with the high polar character of the former reaction. Bonding Evolution Theory accounts for the cb-type reactivity of nitrile imine. Along the more favourable ortho regioisomeric path a…