Search results for "Lope"
showing 10 items of 2014 documents
Asymmetrische Hetero-Diels-Alder-Reaktionen in wäßriger Lösung unter Verwendung von Aminosäureestern als chiralen Auxiliaren
1989
(R)- und (S)-Aminosaure-methylester-hydrochloride bilden mit Formaldehyd in THF/Wasser-Gemischen Iminium-Ionen, die als elektronenarme Dienophile mit Cyclopentadien, 1,3-Cyclohexadien und Alkyl-substituierten Butadienen bereits bei 0°C Hetero-Diels-Alder-Reaktionen eingehen. Die Cycloaddukte werden mit hohen Ausbeuten im Multigrammasstab und mit Diastereomerenverhaltnissen (bis zu 93:7) gebildet, die mit anderen chiralen Aminen bisher nicht erreicht werden konnten. Mit Hilfe von NOE-Experimenten werden die absoluten Konfigurationen der Hauptdiastereomeren zugeordnet. Aus den Phenylglycin- und den Serin-Derivaten konnen die chiralen Hilfsgruppen mittels hydrogenolytischer Methoden bzw. unter…
Hantzsch Ester-Mediated Photochemical Transformations in the Ketone Series: Remote C(sp3)–H Arylation and Cyclopentene Synthesis through Strain Relea…
2021
A metal-free Hantzsch ester-mediated synthesis of cyclopentenylketones as well as γ-hetarylketones starting from ketocyclopropanes under eco-friendly conditions was developed. The versatility of the developed conditions is shown by reacting ketocyclopropanes in both a formal [3 + 2] cycloaddition with terminal alkynes (further investigated using theoretical calculations) and a radical C-C-coupling with cyanopyridines. The newly developed methodologies were later on utilized as a downstream reaction for photogenerated cyclopropanes combining UV and visible light photochemistry. Following this procedure, a UV-driven Norrish-Yang-type reaction induces the ring strain of the intermediates, whic…
Single-Component Polymerization Catalysts for Ethylene and Styrene: Synthesis, Characterization, and Reactivity of Alkyl and Hydrido Yttrium Complex…
1999
Yttrium alkyl complexes Y(η5:η1-C5Me4SiMe2NCMe2R)(CH2SiMe3)(THF) (R = Me, Et) and Y(η5:η1-C9H6SiMe2NCMe3)(CH2SiMe3)(THF) can be prepared in high yields by a σ-bond metathesis reaction between Y(CH2SiMe3)3(THF)2 and amino-functionalized cyclopentadienes or indene. The structure of Y(η5:η1-C5Me4SiMe2NCMe2Et)(CH2SiMe3)(THF) was shown by single-crystal X-ray diffraction to be that of a three-legged piano stool. Reaction of Y(CH2SiMe3)3(THF)2 with the tridentate linked amido−cyclopentadienyl ligands (C5Me4H)SiMe2NHR (R = CH2CH2OMe, CH2CH2NMe2, CH2CH2CH2OMe, CMe2CH2OMe), which contain an additional donor site, results in the cleavage of the silicon−cyclopentadienyl bond and the formation of the t…
Alkyl Complexes of Rare-Earth Metals That Contain a Furyl-Functionalized Cyclopentadienyl Ligand: Alkyl Cation Formation and Unexpected Ring-Opening…
2003
Rare-earth metal complexes of the type [Ln{η5:η1-C5Me4SiMe2(C4H3O-2)}(CH2SiMe3)2(THF)] (Ln = Y, Lu) were prepared by σ-bond metathesis of [Ln(CH2SiMe3)3(THF)2] with the 2-furyl-functionalized tetramethylcyclopentadiene (C5Me4H)SiMe2(C4H3O-2) and isolated as colorless crystals. Single-crystal X-ray structure analysis of the lutetium complex confirmed the coordination of the furyl group and THF to give a molecule of trigonal bipyramidal geometry with the oxygen donor atoms in the apical positions. The lability of the oxygen donor atoms results in fluxional behavior. Reaction with triphenylborane in THF gave thermally robust mono(alkyl) cations [Ln{η5:η1-C5Me4SiMe2(C4H3O-2)}(CH2SiMe3)(THF)n]+.…
Linked Benzylamido-Cyclopentadienyl Ligands: Synthesis and Characterization of Alkyl Titanium Complexes
1997
Titanium complexes of the general type Ti(η5:η1-C5H4Si-Me2NCH2C6H3X2-2,5)Cl2 (XH, F), containing a linked benzylamido-cyclopentadienyl ligand, were prepared by reaction of Ti(η5-C5H4SiMe2Cl)Cl3 with lithium amide Li(NHCH2C6H3X2-2,5). A single-crystal X-ray structural analysis of Ti(η5: η1-C5H4SiME2NCH2C6H3F2-2,5)Cl2 revealed a conformation in the solid state in which the aryl ring is turned away from the metal center. Ti(η5:η1-C5H4SiMe2NCH2C6H5)Cl2 can be alkylated with a variety of reagents to form extremely sensitive complexes of the type Ti(η5-C5H4SiMe,2NCH2C6H5)R2 (RMe, CH2 C6H5, CH2SiME3, CH2CMe2C6H5). Reaction of Li2[C5Me4SiMe2NCH2C6H5] with TiCl3(THF)3 gave Ti(η5: η1-C5Me4SiMe2NCH2C6…
Functional Enzyme Mimics for Oxidative Halogenation Reactions that Combat Biofilm Formation
2017
Transition-metal oxide nanoparticles and molecular coordination compounds are highlighted as functional mimics of halogenating enzymes. These enzymes are involved in halometabolite biosynthesis. Their activity is based upon the formation of hypohalous acids from halides and hydrogen peroxide or oxygen, which form bioactive secondary metabolites of microbial origin with strong antibacterial and antifungal activities in follow-up reactions. Therefore, enzyme mimics and halogenating enzymes may be valuable tools to combat biofilm formation. Here, halogenating enzyme models are briefly described, enzyme mimics are classified according to their catalytic functions, and current knowledge about th…
ortho-Metalation of aromatic ethers by yttrium alkyl complexes that contain a linked amido-cyclopentadienyl ligand
2003
Abstract The reaction of the half-sandwich alkyl complex [Y(η5:η1-C5Me4CH2SiMe2NtBu)(CH2SiMe3)(THF)] (1) with anisole smoothly gives the ortho-metalation product [Y(η5:η1-C5Me4CH2SiMe2NtBu)(2-C6H4OMe)(THF)] (2). 3- and 4-Methylanisole as well as phenetole analogously undergo ortho-metalation, whereas thioanisole, N,N′-dimethylaniline, fluorobenzene, and trifluorobenzene do not react with yttrium complex 1. 2-Methylanisole reacts with 1 under activation of the ring methyl group to give the 2-methoxybenzyl complex [Y(η5:η1-C5Me4CH2SiMe2NtBu)(CH2C6H4OMe-2)(THF)] (6). A single-crystal X-ray structure analysis of the 2-anisyl complex 2 revealed a four-legged piano-stool configuration with the me…
(Co-)solvent selection for single-wall carbon nanotubes: best solvents, acids, superacids and guest-host inclusion complexes.
2011
Analysis of 1-octanol-water, cyclohexane-water and chloroform (CHCl(3))-water partition coefficients P(o-ch-cf) allows calculation of molecular lipophilicity patterns, which show that for a given atom log P(o-ch-cf) is sensitive to the presence of functional groups. Program CDHI does not properly differentiate between non-equivalent atoms. The most abundant single-wall carbon nanotube (SWNT), (10,10), presents a relatively small aqueous solubility and large elementary polarizability, P(o-ch-cf) and kinetic stability. The SWNT solubility is studied in various solvents, finding a class of non-hydrogen-bonding Lewis bases with good solubility. Solvents group into three classes. The SWNTs in so…
Synthesis of novel isoxazoline-fused cispentacin stereoisomers
2009
Abstract New isoxazoline-fused cispentacins were prepared by the 1,3-dipolar cycloaddition of nitrile oxides to β-amino esters containing a cyclopentene skeleton. This synthetic procedure gave regio- and diastereoisomers of the cispentacins. The synthetic route was extended to the synthesis of these compounds in enantiomerically pure form.
Feature characterization of scarring and non-scarring types of alopecia by multiphoton microscopy (Conference Presentation)
2018
Treatment and management of alopecia are highly determined by an accurate diagnosis, which can be challenging due to the lack of methods to properly visualize hair follicles. Current standard diagnosis is based on dermoscopy for non-scarring alopecia and scalp biopsy for scarring types of alopecia. Dermoscopy can be inconclusive, while biopsy is a painful procedure. In this study, we used a clinical tomograph based on multiphoton microscopy (MPM) to non-invasively image the scalp of 5 healthy subjects and of 12 patients affected by non-scarring alopecia (androgenetic and areata) and scarring alopecia (frontal fibrosing). MPM is capable of non-invasive in vivo imaging of follicular structure…