Search results for "Reaction"
showing 10 items of 6134 documents
ChemInform Abstract: Catalytic Enantioselective Friedel-Crafts Reactions of Naphthols and Electron-Rich Phenols
2016
The enantioselective Friedel–Crafts reaction is a powerful tool for the construction of benzylic stereocenters in a stereodefined manner. Significant advances have already been achieved with heteroarenes such as indoles and pyrroles; however, the reaction with homoarenes is less developed. This short review covers the most relevant literature on enantioselective Friedel–Crafts reactions with naphthols and phenols. 1 Introduction 2 Friedel–Crafts Reactions Involving 1,2-Nucleophilic Addition to C=X Bonds 3 Friedel–Crafts Reactions Involving Conjugate Nucleophilic Addition to Electrophilic C=C Bonds 4 Friedel–Crafts Reactions Involving π-Allylic Complexes as Electrophiles 5 ipso-Friedel–Craft…
Kinetik der bromierung von phenolen und phenolischen mehrkernverbindungen, 2. Die reaktionsfähigkeit isomerer zweikernverbindungen
1976
Die Geschwindigkeit der Bromierung von 6 isomeren Zweikernverbindungen mit jeweils einer reaktionsfahigen Stelle (Hydroxydimethylbenzyl-methylphenole 1, 2 und 3) wurde in Eisessig bei 22°C UV-spektroskopisch bestimmt. Fur die Reaktion in ortho-Stellung zur phenolischen Hydroxy-Gruppe ergibt sich eine Verminderung der Geschwindigkeit um den Faktor 3–3,5 wenn zwischen den Hydroxy-Gruppen der beiden Phenolbausteine eine intramolekulare Wasserstoffbrucke sterisch moglich ist (1a). In den anderen Fallen (1b, 2a, 2b) verlauft die Bromierung ungefahr ebenso schnell wie bei 2,4-Dimethylphenol. Die schneller verlaufende Reaktion in para-Stellung (3a, 3b) wird durch eine Wasserstoffbrucke um den Fakt…
Der nachweis der primärreaktion bei der autoxydation des tetralins
1964
Die Autoxydation des Tetralins wurde bei kleinen Umsatzen durch polarographische oder kolorimetrische Bestimmung des Peroxidgehaltes verfolgt und eine Anfangsgeschwindigkeit gefunden, die groser ist, als sie nach dem Peroxidgehalt des Tetralins sein sollte. Diese zusatzliche Reaktionsgeschwindigkeit ist die der Primarreaktion der Autoxydation. Dabei bilden sich aus Tetralin und molekularem Sauerstoff Radikale. Diese Primarreaktion ist nur dann beobachtbar, wenn der Peroxidgehalt des Tetralins etwa 10−5 Mol/l betragt oder kleiner ist. The autoxidation of tetraline was measured to a low degree of conversion by polarographic or colorimetric determination of tetraline hydroperoxide. The extrapo…
Antidiabetische wirkstoffe. III. 4,5,6-Trisubstituierte 2-(4-toluidino)pyrimidine
1984
Aus der Kondensation von 4-Tolylguanidin (1) mit den β-Diketonen 2a-b gehen die 2-(4-Toluidino)pyrimidine 3a-b hervor. The condensation of 4-tolyiguanidine (1) with the β-kiketones 2a-b yields the 2-(4-toluidino)pyrimidines 3a-b.
Trichomonazide Wirkstoffe, 2. Mitt. Verzweigtkettig 4,6-disubstituierte 2-Cyanaminopyrimidine
1985
Aus der Umsetzung von Dicyandiamid (1) mit den β-Diketonen 2a–b gehen die 4,6-verzweigtkettig disubstituierten 2-Cyanaminopyrimidine 3a–b hervor. Fur Strukturtyp 3 last sich aus den spektroskopischen Daten, speziell aus den 1H- und 13C-NMR-Werten, das Vorliegen eines Gleichgewichts zwischen den tautomeren 2-Cyanamino- und 2-Cyaniminopyrimidinformen ableiten. 3 zeichnet sich durch trichomonazide, antivirale und antimykotische Wirkung aus. Trichomonacidal Agents, II: 4,6-Disubstituted 2-(Cyanoamino)pyrimidines Carrying Branched Substituents The reaction of dicyandiamide (1) with the β-diketones 2a–b yields the 4,6-branched disubstituted 2-(cyanoamino)pyrimidines 3a–b. From spectroscopic evide…
Concerning the reaction mechanism of the anionic polymerization of styrene in tetrahydrofuran
1969
Photocatalytic oxidation of cyanide in aqueous TiO2 suspensions irradiated by sunlight in mild and strong oxidant conditions
1999
Abstract The photocatalytic oxidation of free cyanide ions was carried out in aqueous aerated suspensions containing polycrystalline TiO2 (anatase) irradiated by sunlight. The influence of the presence of an organic compound (phenol) or of a strong oxidant (H2O2) on the photoprocess was also studied. The dependence of cyanide photo-oxidation rate on the following parameters: (1) cyanide concentration; (2) catalyst amount; and (3) phenol concentration was investigated. At the used experimental conditions, the kinetics of cyanide photo-oxidation is independent of the initial cyanide concentration and of the catalyst amount while it is affected by the phenol concentration and by the presence o…
DFT Study of the Molecular Mechanism of Lewis Acid Induced [4 + 3] Cycloadditions of 2-Alkylacroleins with Cyclopentadiene
2009
The mechanism of the Lewis acid (AlCl(3)) induced [4 + 3] cycloaddition of 2-methylacrolein with cyclopentadiene (Cp) [ J. Am. Chem. Soc. 2004, 126, 2692] has been examined here through DFT calculations at the MPW1K(DCM)/6-31+G** level. Formation of these seven-membered carbocycles is a domino process that comprises three consecutive reactions. The first one is a polar Diels-Alder reaction that is initialized by the nucleophilic attack of Cp to the beta-conjugated position of acrolein, yielding the formation of the endo and exo [4 + 2] cycloadducts. The corresponding LA-[4 + 2] cycloadduct complexes equilibrate through a skeleton rearrangement with a low free activation energy with two seve…
Why do Electron-Deficient Dienes React Rapidly in Diels?Alder Reactions with Electron-Deficient Ethylenes? A Density Functional Theory Analysis
2004
The Diels−Alder reaction of the electron-deficient (ED) dimethyl 2,3-dimethylenesuccinate with two electron-rich (ER) and two ED ethylenes has been studied at the B3LYP/6-31G* level of theory. The analysis of the geometry and electronic structure of the transition state of the reaction with the ED dimethyl 2-methylenemalonate along with the analysis of the global and local electrophilicity indices of the reagents provide an explanation of the participation of this ED diene as nucleophile against powerful electrophiles in polar Diels−Alder reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Mechanism of the oxidation of sulfides by dioxiranes: conformational mobility and transannular interaction in the oxidation of thianthrene 5-oxide.
2004
The detailed study of the oxidation of thianthrene 5-oxide (1) with methyl(trifluoromethyl)dioxirane (5b) in different solvents and in the presence of (18)O isotopic tracers is reported. Thianthrene 5-oxide (1) is a flexible molecule in solution, and this property allows for transannular interaction of the sulfoxide group with the expected zwitterionic 7 and hypervalent 10-S-4 sulfurane 9 intermediates formed in the oxidation and biases the course of the reaction toward the monooxygenation pathway.