Search results for "Reaction"
showing 10 items of 6134 documents
Hydrophobic Encapsulated Phosphonium Salts-Synthesis of Weakly Coordinating Cations and their Application in Wittig Reactions
2015
Large and rigid tetraarylphosphonium tetrafluoroborate salts have been synthesized representing weakly coordinating cations with diameters of several nanometers. Divergent dendritic growth by means of thermal Diels-Alder cycloaddition was employed for the construction of the hydrophobic polyphenylene framework up to the third generation. X-ray crystal structure analysis of first-generation phosphonium tetrafluoroborate supported the rigidity of the non-collapsible shell around the phosphorus center and gave insight into solid-state packing and cation-anion distances. Copper(I)-catalyzed azide-alkyne ligation served as reliable method for the preparation of a first-generation triazolylphenyl…
Unexpected metal-free synthesis of trifluoromethyl arenes via tandem coupling of dicyanoalkenes and conjugated fluorinated sulfinyl imines
2021
A novel strategy for the synthesis of policyclic trifluoromethyl arenes has been devised. It involves a DBU-promoted tandem cycloaromatization reaction of dicyanoalkenes and fluorinated conjugated sulfinyl imines. This unprecedented transformation is a metal-free and air-tolerant process that takes place from readily available starting materials under mild reaction conditions.
Die Synthese reiner Oligo[hydroxy-5-nitro1,3-phenylen)-methylen]e, Verbindungen mit mehreren ortho- bzw. para-Nitrophenolbausteinen im Molekül
1976
Zur Synthese der Oligo[(hydroxy-5-nitro-1,3-phenylen)methylen]e dienten chlormethylierte Nitrophenole sowie mono- und bischlormethylierte Bis- und Tris[(hydroxy-5-nitro-1,3-phenylen)methylen]e. Die Chlormethylierung erfolgte durch Umsetzung mit Chlormethylmethylather in Gegenwart von Zinkchlorid. Die Synthese der Oligomeren gelang mit guten Ausbeuten, wenn die chlormethylierten Verbindungen mit stark uberschussigem Nitrophenol und Zinkchlorid als Katalysator kondensiert wurden. Reaktionsbedingungen und unterschiedliche Reaktionsfahigkeiten werden mitgeteilt. Einige Verbindungen wurden in ihrer Struktur bestatigt, indem sie auf zwei voneinander unabhangigen Wegen dargestellt wurden. Damit wa…
N-Glycosyl Amides as Glycosyl Donors in Stereoselective Glycosylation Reactions
2004
Due to their high stability, N-glycosyl amides have so far not been considered as glycosyl donors for glycosylation reactions. Two new procedures for the cleavage of the anomeric amide functionality under mild reaction conditions and further stereoselective in situ conversions of the activated glycosyl donors with alcohols and amines to give β-configured O- and N-glycosides are described in this article.
ChemInform Abstract: Cross-Metathesis Reactions as an Efficient Tool in the Synthesis of Fluorinated Cyclic β-Amino Acids.
2009
The synthesis of enantiomerically pure, cyclic, gamma,gamma-difluorinated beta-amino acids with various ring sizes has been carried out with a cross-metathesis (CM) reaction being one of the key steps, followed by a Dieckmann-type condensation to bring about the cyclization. Subsequent catalytic hydrogenation under microwave irradiation with (-)-8-phenylmenthol as a chiral auxiliary led to the successful chemo- and diastereoselective chemical reduction of the resulting cyclic beta-enamino esters. The efficiency and scope of the CM reaction with different types of fluorinated imidoyl chlorides and unsaturated esters has also been studied in order to determine the optimal reaction conditions …
Ir-Catalyzed Cycloaddition of Tribenzocyclyne with Biphenylenes
2021
We demonstrate that Ir-catalyzed C-C bond activation in biphenylenes followed by a reaction with tribenzocyclyne is a suitable method for synthesizing strained and unknown monoadducts with the tetradehydrotetrabenzo[a,c,e,i]cyclododecene scaffold ([12]annulenes). Modification of reaction conditions also furnished [12]annulene products with cis and/or trans double bonds formed by hydrogen transfer. The [9]annulene side product was formed upon the reaction of the benzyl radical with tribenzocyclyne during the Bergman cyclization. All isolated compounds were fully characterized by HRMS, NMR, and X-ray diffraction analysis.
The effect of reaction conditions on the chain end structure and functionality during dehydrochlorination oftert-chlorine-telechelic polyisobutylene …
1998
Dehydrochlorination of tert-chlorine-telechelic polyisobutylene with potassium tert-butoxide in refluxing tetrahydrofuran is quantitative after 22 h, but results in ca. 3% endo olefin chain ends which are not reactive in some subsequent functionalization reactions. The formation of these undesired structures is most likely due to simultaneous thermally induced HCl loss. Lower temperatures and longer reaction times led to exclusive formation of external double bonds in some cases but to incomplete dehydrochlorination.
Untersuchungen von polymeren im massenspektrometer, 4. Abbaureaktionen von polybenzylen
1974
Die Abbaureaktionen von unsubstituierten Poly(1,4-phenylenmethylen)en (A) (Polybenzylen), Poly[(2,5-dimethyl-1,4-phenylen)methylen] [Poly(2,5-dimethylbenzyl)] (B), Poly[(2,3,5,6-tetramethyl-1,4-phenylen)methylen] [Poly(2,3,5,6-tetramethylbenzyl)] (C) und Poly(1,4-phenylenathyliden) [Poly(α-methylbenzyl)] (D) wurden durch direkte Pyrolyse im Massenspektrometer untersucht. Die Massenpyrogramme von unter verschiedenen Reaktionsbedingungen dargestellten Polybenzylen wurden verglichen, mit dem Ziel, direkt Informationen uber Strukturunterschiede wie Kettenverzweigung und unterschiedliche Verknupfung der Benzyleinheiten zu erhalten; hierbei konnten in einem Falle auf hohere Kettenverzweigung deut…
ChemInform Abstract: Selective Formal Transesterification of Fluorinated 2-(Trimethylsilyl)ethyl α-Imino Esters Mediated by TBAF.
2008
The scope of the transesterification reaction between β-fluorinated α-imino esters and various electrophiles in the presence of TBAF as fluorine source is described. The reaction is highly selective for alkyl iodides, bromides, and mesylates, while alkyl chlorides react at a significantly slower rate and tosylates do not react under the reaction conditions. This methodology represents a simple and useful alternative for the preparation of a wide variety of fluorinated α-imino esters.
Kinetische Untersuchungen über die kationische Polymerisation von wasserfreiem Formaldehyd. 40. Mitt. Über polyoxymethylene
1971
Die Polymerisation von Formaldehyd in atherischer Losung bei −78°C mit SnCl4 und HClO4 als Initiatoren wurde untersucht. Die Konzentration der aktiven Zentren (Polyoxymethylen-Kationen) wurde bestimmt, indem die Polymerisationen durch Zugabe eines grosen Uberschusses an n-Amylalkohol abgebrochen und die entstandenen Pentoxylendgruppen nach Reinigung und Hydrolyse der Polymeren gaschromatographisch bestimmt wurden. Die Initiierung der Polymerisationerfolgt rasch und fuhrt zu vollstandigem Umsatz des Initiators wahrend der ersten Minuten. Unter gunstigen Reaktionsbedingungen ergibt jedes eingesetzte Initiatormolekul ein Polyoxymethylene-Kation. Ein kinetischer Abbruch wurde nicht festgestellt…