Search results for " Cycloaddition"
showing 10 items of 67 documents
Straightforward Regio- and Diastereoselective Synthesis, Molecular Structure, Intermolecular Interactions and Mechanistic Study of Spirooxindole-Engr…
2021
Straightforward regio- and diastereoselective synthesis of bi-spirooxindole-engrafted rhodanine analogs 5a–d were achieved by one-pot multicomponent [3 + 2] cycloaddition (32CA) reaction of stabilized azomethine ylide (AYs 3a–d) generated in situ by condensation of L-thioproline and 6-chloro-isatin with (E)-2-(5-(4-chlorobenzylidene)-2,4-dioxothiazolidin-3-yl)-N-(2-morpholinoethyl)acetamide. The bi-spirooxindole-engrafted rhodanine analogs were constructed with excellent diastereo- and regioselectivity along with high chemical yield. X-ray crystallographic investigations for hybrid 5a revealed the presence of four contiguous stereocenters related to C11, C12, C19 and C22 of the spiro struct…
A density functional theory study of the regio- and stereoselectivity of the 1,3-dipolar cycloaddition of C-methyl substituted pyrazinium-3-olates wi…
2013
Abstract A DFT [B3LYP/6-31G(d)] study was carried out on the 1,3-dipolar cycloaddition (13DC) reactions of multi C-methyl substituted pyrazinium-3-olates with methyl acrylate (MA) and methyl methacrylate (MMA). Thermodynamic and kinetic parameters of the possible endo/exo stereoisomeric and 6-ester/7-ester regioisomeric pathways have been determined. The skeleton rearrangement of the 6-exo [3 + 2] cycloadducts into the [4 + 2] adducts is also considered. The electrophilic, P k + , and nucleophilic, P k - , Parr functions are used to have better understanding of the regioselectivity of these 13DC reactions. In all cases the exo pathways are more favourable compared to the endo alternatives. …
Theoretical study of 1,3-dipolar cycloaddition reactions with inverse electron demand - A DFT study of the lewis acid catalyst and solvent effects in…
2000
The molecular mechanism for the inverse electron demand 1,3-dipolar cycloaddition of nitrones with vinyl ethers has been characterized using density functional theory methods with the B3LYP functional and the 6−31G* basis set. Relative rates, regioselectivity, endo/exo stereoselectivity, Lewis acid catalyst and solvent effects are analyzed and discussed. Four reactive channels associated with the formation of two pairs of diasteromeric regioisomers have been characterized. Analysis of the geometries of the corresponding transition structures shows that the reaction in the gas phase takes place by an asynchronous concerted mechanism. These 1,3-dipolar cycloadditions present a large ortho reg…
Unravelling [3+2] Cycloaddition Reactions through the Molecular Electron Density Theory
2018
Después de la primera clasificación de las reacciones 32CA en reacciones de tipo zw y pr, establecidas en el año 2014, la estructura y reactividad de los TACs más importantes utilizados en las reacciones 32CA ha sido completamente caracterizado en base a la MEDT propuesta recientemente. Entre la gran cantidad de trabajo desarrollado a lo largo de la presente tesis doctoral, se han seleccionado y discutido ocho publicaciones representativas, que permitieron caracterizar dos nuevos tipos de reactividad y consolidar la reactividad original de tipo zw. Así, dependiendo de las cuatro estructuras electrónicas diferentes de los TACs, es decir, pseudodiradical, pseudoradical, carbenoide y zwitterió…
Unveiling the Different Reactivity of Bent and Linear Three-Atom-Components Participating in [3 + 2] Cycloaddition Reactions
2021
The reactivity of a series of pairs of bent and linear three-atom-component (B-TACs and L-TACs) participating in [3 + 2] cycloaddition (32CA) reactions towards ethylene and electrophilic dicyanoethylene (DCE) have been studied within the Molecular Electron Density Theory. While the pseudodiradical structure of B-TACs changes to that of pseudoradical or carbenoid L-TACs upon dehydrogenation, zwitterionic B-TACs remain unchanged. Conceptual Density Functional Theory (CDFT) indices characterize five of the nine TACs as strong nucleophiles participating in polar reactions towards electrophilic ethylenes. The activation energies of the 32CA reactions with electrophilic DCE range from 0.5 to 22.0…
Design, Construction, and Characterization of a New Regioisomer and Diastereomer Material Based on the Spirooxindole Scaffold Incorporating a Sulphon…
2020
The 1,3-dipolar cycloaddition reaction is one of the most rapid, and efficient protocols to access, and construct highly divergent heterocycle chiral auxiliaries. Free catalyst synthesis of spirooxindole scaffold incorporating sulphone moiety via one pot&ndash
Synthesis of conformationally restricted 1,2,3-triazole-substituted ethyl β- and γ-aminocyclopentanecarboxylate stereoisomers. Multifunctionalized al…
2010
Abstract Stereoisomers of 1,2,3-triazole-functionalized, conformationally restricted β- or γ-amino esters with a cyclopentane skeleton were efficiently synthetized from the bicyclic β-lactam 6-azabicyclo[3.2.0]hept-3-en-7-one (1) and Vince γ-lactam (15) in five or six steps involving the azide–alkyne 1,3-dipolar cycloaddition of azido-substituted amino ester stereoisomers with nonsymmetric acetylenes. The azide–alkyne click reactions were investigated under thermal and Cu(I)-catalyzed conditions. Surprisingly, the thermally induced cycloaddition furnished the corresponding 1,4-triazoles regioselectively, which also took place selectively in response to Cu(I) catalysis.
The ultrasounds-ionic liquids synergy on the copper catalyzed azide-alkyne cycloaddition between phenyl acetylene and 4-azidoquinoline
2015
Abstract The effect of ultrasound irradiation on the copper catalyzed azide–alkyne cycloaddition between phenylacetylene and 4-azidoquinoline has been studied in solution of different ionic liquids. In particular, we used ionic liquids featuring both aliphatic and aromatic mono- and dications, as well as anions differing in size, symmetry and coordination ability. We also examined the influence of the ionic liquids structural features on the reaction outcomes, finding that under magnetic stirring reactivity is favorably affected by the solvent structural organization, while under sonochemical conditions an opposite trend was observed. In all cases examined, sonochemical activation leads to …
An analysis of the regioselectivity of 1,3-dipolar cycloaddition reactions of benzonitrile n-oxides based on global and local electrophilicity and nu…
2009
The regioselectivity of the 1,3-dipolar cycloaddition (13DC) reactions of benzonitrile N-oxides (BNOs) with electrophilic and nucleophilic alkenes has been analyzed by using global and local nucleophilicity and electrophilicity reactivity indices defined within the conceptual DFT. The BNOs react with electron-deficient and electron-rich ethylenes, but the regioselectivities of these polar reactions are different. Whereas the reactions with electron-rich ethylenes are completely regioselective, yielding 5-isoxazolines, a change in the regioselectivity is observed in the reactions with electron-deficient ethylenes, which yield a mixture of 4- and 5-isoxazolines. Analysis of the energies, geom…
Cyclodextrin-[60]fullerene conjugates: synthesis, characterization, and electrochemical behavior
2006
Three different functionalized β-cyclodextrins (β-CDs) bearing the C60 moiety linked covalently have been prepared in good yields by reaction between the parent β-CD and [60]fullerene via 1,3-dipolar cycloaddition. These compounds have been fully spectroscopically characterized and their electrochemical behavior has been investigated. Surprisingly, the electrochemical properties of the C60 cage remain unaltered even after chemical functionalization, making these systems very appealing as supramolecular hosts for electron-transfer processes.