Search results for "Vinyl ether"
showing 8 items of 18 documents
A mechanistic study of the participation of azomethine ylides and carbonyl ylides in [3+2] cycloaddition reactions
2015
The participation of azomethine ylides (AYs) and carbonyl ylides (CYs) in [3+2] cycloaddition (32CA) reactions has been analysed at the DFT B3LYP/6-31G(d) level. The asymmetric substitution breaks the pseudodiradical character of the simplest three-atom-components (TACs), modifying their electrophilic and nucleophilic behaviours. These TACs react quickly towards electrophilic nitroethylene. However, while the reaction with AY takes place via a zw-type mechanism, the reaction with CY appears to take place via a pr-type mechanism. A different behaviour is found in the reactivity towards the nucleophilic methyl vinyl ether. While AY presents a high activation energy, CY presents a high reactiv…
Lewis Acid Induced [2+2] Cycloadditions of Silyl Enol Ethers with α,β-Unsaturated Esters: A DFT Analysis
2005
The Lewis acid (LA) induced cycloaddition of trimethysilyl vinyl ether with methyl acrylate has been studied by DFT methods at the B3LYP/6-31G* level. In the absence of an LA, a [4+2] cycloaddition between the silyl enol ether and methyl acrylate in the s-cis conformation takes place through an asynchronous, concerted bond-formation process. This cycloaddition presents a large activation enthalpy of 21.1 kcal mol–1. Coordination of the LA AlCl3 to the carbonyl oxygen atom of methyl acrylate yields a change of molecular mechanism from a concerted to a two-step mechanism and produces a drastic reduction of the activation energy. This stepwise mechanism is initialized by the nucleophilic attac…
A density functional theory study of the chemoselectivity and regioselectivity of the domino cycloaddition reactions of nitroalkenes with substituted…
2000
The chemoselectivity and regioselectivity of the domino intermolecular [4 + 2]/[3 + 2] cycloaddition reactions of nitroalkenes with substituted alkenes, vinyl ethers as electron-rich alkenes and vinyl ketones as electron-poor alkenes, have been studied using density functional theory (DFT) methods with the B3LYP functional and the 6-31G* basis set. These domino processes comprise two consecutive cycloaddition reactions: the first one is an intermolecular [4 + 2] cycloaddition of the vinyl ether to the nitroalkene to give a nitronate intermediate, which then affords the final nitroso acetal adduct through an intermolecular [3 + 2] cycloaddition reaction with the vinyl ketone. The two consecu…
Electron-transfer reduction of selected alcohols with alkalide K−, K+(15-crown-5)2 via organometallic intermediates
2004
Abstract The course of the reaction of alkalide K − , K + (15-crown-5) 2 1 with selected alcohols depends on the kind of alcohol and the mode of substrate delivery. In the case of methanol, potassium methoxide formed initially undergoes destruction at the excess of 1 . It results in potassium oxide and methylpotassium. The latter opens the crown ether ring giving potassium tetraethylene glycoxide vinyl ether and methane. A similar course of the process is observed for propanol. Potassium glycidoxide is the main product formed in the reaction of 1 with glycidol. Its oxirane ring is opened at the excess of 1 . Organopotassium alkoxides, i.e., potassium potassiomethoxide and dipotassium potass…
Anorganische verbindungen als lösungsmittel für polymere und monomere. Polymerisationen in phosphoroxychlorid und thionylchlorid
1966
Die Loslichkeit verschiedener Monomerer, Polymerer und Polymerisationskatalasatoren in anorganischen Verbindungen wurde untersucht. Chloride und Oxychloride des Phosphors und Schwefels zeigten gute Losungseigenschaften. Thionylchlorid und Phosphoroxychlorid wurden als Losungsmittel bei der kationischen Polymerisation von Styrol, Isobutylvinylather, 3,3-Bis-(chlormethyl)-oxetan, Tetrahydrofuran und Epichlorhydrin eingeaetzt. Als geeignete Katalysatoren erwiesen sich hierbei Aluminiumchlorid und Eisentrichlorid. In Phosphoroxychlorid konnten Acrylnitril und Vinylchlorid radikalisch polymerisiert werden. The solubility of a series of monomers, polymers, and initiators in inorganic compounds wa…
Influence of Reactant Polarity on the Course of the Inverse-Electron-Demand Diels−Alder Reaction. A DFT Study of Regio- and Stereoselectivity, Presen…
1999
The molecular mechanisms for the inverse-electron-demand Diels−Alder reactions between nitroethene and three substituted ethenes (propene, methyl vinyl ether, and dimethylvinylamine) to give the corresponding nitroso cycloadducts have been characterized with density functional theory methods using the B3LYP/6-31G* calculational level. On the basis of stability arguments and molecular orbital analysis relative rates, regioselectivity, and stereoselectivity, the presence of Lewis acid catalyst modeled by the BH3 system and the inclusion of solvent effects as a function of the nature of substituent in the dienophile fragment are analyzed and discussed. The ortho attack mode presents transition…
ChemInform Abstract: Influence of Reactant Polarity on the Course of the Inverse-Electron-Demand Diels-Alder Reaction. A DFT Study of Regio- and Ster…
2010
The molecular mechanisms for the inverse-electron-demand Diels−Alder reactions between nitroethene and three substituted ethenes (propene, methyl vinyl ether, and dimethylvinylamine) to give the corresponding nitroso cycloadducts have been characterized with density functional theory methods using the B3LYP/6-31G* calculational level. On the basis of stability arguments and molecular orbital analysis relative rates, regioselectivity, and stereoselectivity, the presence of Lewis acid catalyst modeled by the BH3 system and the inclusion of solvent effects as a function of the nature of substituent in the dienophile fragment are analyzed and discussed. The ortho attack mode presents transition…