Search results for "cyclic"
showing 10 items of 2439 documents
Reaktionen von Benzothiet mit Iminen
1993
Reactions of Benzothiete with Imines A great variety of compounds 3a–w containing CN double bonds was studied in the reaction with benzothiete (1). H, alkyl, aryl, OR, SR and NR groups can be attached to the imino function. The azomethines 3a–f, the thiazolines 3g–i, the lactim 3n, the oximes 3r–t, the isoxazolinone 3u and the azine 3v show [8π + 2π] cycloaddition reactions yielding derivatives of 1,3-benzothiazine (4a–i, n, r–v). In the case of 4n, s, t secondary reactions occur, initiated by elimination processes. [8π + 2π] Cycloadditions account also for the reactions 3e 10, 11, 3o 18(I), and 3q 19; however, CC double bonds are representing the 2π component in these examples. The thiazol…
ChemInform Abstract: Asymmetric Synthesis of Bicyclic Amino Acid Derivatives by Aza-Diels- Alder Reactions in Aqueous Solution.
2010
Derivatives 7–10 and 13–16 of methyl and ethyl 2-azabicyclo[2.2.1]heptane-3-carboxylates are synthesized by Aza-Diels-Alder reactions of chiral iminium ions, formed in situ from glyoxylic acid and chiral amines, with cyclopentadiene. Whereas the heterodienophiles derived from phenylglycinol and esters of sterically more demanding amino acids fail to undergo asymmetric cycloadditions, with alanine methyl ester and (R)-1-phenylethylamine hydrochoride the cycloadducts are formed in yields of 15 and 52%, respectively, reaching de values of up to 90:10 for the exo isomers.
Naphthalenophane durch doppelte Photocyclodimerisierung von Distyrylnaphthalinen
1989
Bei der Belichtung von Distyrylnaphthalinen entstehen in regiospezifischen Kopf-Kopf-Cycloadditionen Naphthalenophane. Je nach Stellung der Styryl-Gruppen beobachtet man vollkommen stereospezifische Prozesse (1d 2, 1g 3, 1h 4) und Dimerisierungen mit partiellen Stereoselektivitaten (1b 5–8, 1i 9, 10). Masgeblich sind die Rotamerenpopulation im Ausgangsprodukt 1 und die elektronischen und sterischen Effekte in den Excimeren. Prinzipiell sind Excimere mit paralleler Anordnung moglichst vieler π-Zentren bevorzugt — ein experimenteller Befund, der durch HMO-Rechnungen untermauert wird. Naphthalenophanes by Twofold Photocyclodimerizatio Reactions of Distyrylanaphthalenes Regiospecific head-to-he…
Reaktion von elektronenreichen Heterocyclen mit Orthocarbonsäure-Derivaten, 12. Formylierung von Vinylindolen mit Diethoxycarbenium-tetrafluoroborat
1988
Reactions of Electron-Rich Heterocycles with Orthocarboxylic Acid Derivatives, 12. – Formylation of Vinylindoles with Diethoxycarbenium Tetrafluoroborate 2- and 3-vinylindoles 1, 3 are formylated with diethoxycarbenium tetrafluoroborate regioselectively. The significant selectivity and reactivity of formylation of diethoxycarbenium ion in comparison with other thermodynamically more stable dialkoxycarbenium ions are compatible with the known results of hetaryl functionalisation with orthocarboxylic acid derivatives.
A novel and selective fluoride opening of aziridines by XtalFluor-E. synthesis of fluorinated diamino acid derivatives.
2015
The selective introduction of fluorine onto the skeleton of an aminocyclopentane or cyclohexane carboxylate has been developed through a novel and efficient fluoride opening of an activated aziridine ring with XtalFluor-E. The reaction proceeded through a stereoselective aziridination of the olefinic bond of a bicyclic lactam and regioselective aziridine ring opening with difluorosulfiliminium tetrafluoroborate with the neighboring group assistance of the sulfonamide moiety to yield fluorinated diamino acid derivatives. The method based on the selective aziridine opening by fluoride has been generalized to afford access to mono- or bicyclic fluorinated substances.
New Studies and a Reinvestigation on [4+2] Cycloadditions of (−)-Thebaine: Asymmetrical Diels-Alder Reactions with a Conformationally Fixed Chiral Di…
1993
Some novel Diels-Alder reactions of the opium alkaloid (−)-thebaine (1) as an electron-rich diene and a reinvestigation of its reactions with cyclic and acyclic dienophiles are described. The π-facial selectivity has been studied on the basis of structural analyses of the cycloadducts. Some related results on [4 + 2] cycloaddition reactions of 1-methoxy-1,3-cyclohexadiene (11) are also reported.
Transition metal–saccharide chemistry: synthesis, characterization and solution stability studies of cis-dioxomolybdenum saccharide complexes
1998
Six cis-dioxomolybdenum(VI) complexes of simple monosaccharides (D-glucose, D-fructose, D-galactose, D-mannose, D-ribose and D-xylose) have been synthesized and characterized by a variety of analytical and spectral methods. Both the solution and solid-state studies have supported the presence of dimeric structures, formed through the cis-MoO2 moieties and the bridging saccharide units. Solution stability of these complexes as a function of time has also been addressed.
Synthesis, structure, physicochemical characterization and theoretical evaluation of non-covalent interaction energy of a polymeric copper(II)-hydraz…
2019
Abstract One dimensional polymeric copper-hydrazone complex {[Cu(H0.5L)(µ1,3-SCN)]0.5ClO4·0.5MeOH}n (1) has been synthesized with Cu(ClO4)2·xH2O and N'-(1-(pyridin-2-yl)ethylidene)acetohydrazide (HL) in presence of NaSCN. The ligand and the complex have been characterized by several spectroscopic techniques (IR, UV–Vis and EPR), cyclic voltammetry and the structure of 1 has been determined by single crystal X-ray diffraction. The complex is an infinite one dimensional polymer bridged by thiocyanate. The magneto-structural correlation has been determined and the non-covalent interactions present in the molecule have been energetically evaluated by means of DFT calculations.
Selective Formal Transesterification of Fluorinated 2-(Trimethylsilyl)ethyl α-Imino Esters Mediated by TBAF
2008
The scope of the transesterification reaction between beta-fluorinated alpha-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 alpha-imino esters.
Determination of selected polyaromatic hydrocarbons by gas chromatography–mass spectrometry for the analysis of wood to establish the cause of sinkin…
2014
Abstract The aim of this paper was to establish the cause of sinking of an old wooden vessel by polycyclic aromatic hydrocarbon (PAH) analyses because wood combustion is a source of PAHs. In particular, the molecular PAH patterns generated by each source are like fingerprints and it is possible to determine the processes that generate PAHs by studying their distribution in wood samples. The relative abundance of high molecular weight PAHs, together with the PAH compound ratios and with total index (proposed by us) has demonstrated that samples owe their PAHs in wood archaeological material to a predominant single mode of origin, i.e. combustion processes, therefore we can say that the sinki…