351 research outputs found
Catalyst Structure and Cis-Trans Selectivity in Ruthenium-based Olefin Metathesis
No full textControl of olefin geometry has long proved a challenge in the field of Ru-catalyzed olefin metathesis. Through an understanding of the reaction mechanism, key factors that govern cis–trans selectivity in cross-metathesis applications are identified. These factors are illustrated in the relationship between ligand environment and cis–trans selectivity in several key metathesis catalysts. Recent efforts have culminated in the successful application of ligand-based design strategies in three families of Z-selective metathesis catalysts. The relationships between catalyst structure, stability and Z-selectivity in these systems are discussed
Development of Rhodium Catalyzed Formic Acid Mediated Z-Selective Alkene Synthesis from Electron Deficient Dienes
No full textZ-Alkenes are important functional moieties in biological molecules and serve as versatile units for chemical transformations in synthetic chemistry. Synthetic strategies to readily generate these less thermodynamically stable alkenes with high regio-, chemo- and stereocontrol remain challenging, as these methods require stoichiometric main-group activators or are poorly tolerant of reactive functional groups. Selective hydride addition to electron deficient dienes and their use as pronucleophiles in reductive coupling processes can serve as an alternative to the already existing strategies. This thesis describes the development of a new chemo-, regio-, and stereoselective synthesis of Z-alkenes from electron deficient dienes mediated by formic acid using Rh-catalysis
Synthesis of Boronic Esters from 3-Methoxyphenylboronic Acid for Comparison in Rh-Catalyzed Conjugate Additions
No full textVem är "Maja Lundgren" i Maja Lundgrens Myggor och tigrar? : Fakta och fiktion som ontologi, framställningssätt eller retorisk kommunikationsakt
No full textMaja Lundgren’s outspoken description in Myggor och tigrar (2007) of the male dominated cultural life of Sweden raised an animated debate in media. Well known authors and journalists felt themselves scandalized and accused Lundgren of being paranoid. Others claimed that the narrator and character »Maja Lundgren« was not to be confused with Maja Lundgren the author, because the book was fictional and not factual. In this article I discuss Myggor och tigrar out from different fiction theories and conclude that it seems most rewarding to approach the problem of fictionality as a question of rhetorical communication rather than ontology or stylistic devices. I also maintain that Lundgren’s book would implode if read as fiction, since the rhetorical strategy implies the identity of the author and the character.</p
Vem är »Maja Lundgren« i Maja Lundgrens Myggor och tigrar? Fakta och fiktion som ontologi, framställningssätt eller retorisk kommunikationsakt
No full textSten Wistrand is associate professor in comparative
literature at Örebro University.Maja Lundgren’s outspoken description in Myggor och tigrar
(2007) of the male dominated cultural life of Sweden raised an
animated debate in media. Well known authors and journalists
felt themselves scandalized and accused Lundgren of being
paranoid. Others claimed that the narrator and character
»Maja Lundgren« was not to be confused with Maja Lundgren
the author, because the book was fictional and not factual. In
this article I discuss Myggor och tigrar out from different
fiction theories and conclude that it seems most rewarding to
approach the problem of fictionality as a question of rhetorical
communication rather than ontology or stylistic devices. I also
maintain that Lundgren’s book would implode if read as fiction,
since the rhetorical strategy implies the identity of the
author and the character
Bis(1-adamantyl)(2-morpholinophenyl)phosphine (Mor-DalPhos)
No full text(ligand employed in transition metal-catalyzed reactions)
Alternate Name: di(1-adamantyl)-2-morpholinophenylphosphine.
Physical Data: mp 219–224 °C.
Solubility: soluble in most polar organic solvents.
Form Supplied in: White to pale yellow powder or crystals. Also commercially available as preformed Au-ligand complexes such as (MeCN)(Mor-Dalphos)Au(I) SbF_6 and [Mor-Dalphos]Au(I)Cl.
Analysis of Reagent Purity: NMR, Elemental Analysis.
Preparative Method: Pd-catalyzed cross-coupling of N-(2-bromophenyl)morpholine and diadamantyl phosphine.
Handling, Storage, and Precautions: the phosphine is not particularly sensitive to air or moisture although precautions, such as storage under inert atmosphere in a cool place, should be taken during long-term storage.
Bis(1-adamantyl)(2-morpholinophenyl)phosphine (Mor-DalPhos) is a phosphine ligand that has been employed in Pd-catalyzed cross-coupling reactions and Au-catalyzed hydroamination and [3+2] annulations. This ligand, when combined with an appropriate Pd-source, is particularly effective for promoting selective monoarylation processes between aryl electrophiles and nucleophiles such as ammonia, hydrazine, and acetone
Tuning the properties of protein-based biosensors by chromophore replacement strategies.
No full textOptical imaging of membrane potentials has become an immensely popular approach to study neuronal activity. Over the past decades, a number of voltage indicators have been introduced including the voltage sensitive fluorescent protein (VSFP) and microbial rhodopsins. However, most of these sensors suffer from weak signal-to-noise ratios, low sensitivity and incompatibility for deep tissue imaging. The second Chapter of this thesis describes our current efforts on improving microbial rhodopsinbased voltage indicators by replacing the retinal cofactor with a red shifted analogue. We synthesized the red-shifted retinal analogue (S4) with higher quantum yield and extinction coefficient compared to the natural retinal. Next, we reconstituted the ARCH and PROPS variants using the synthetic retinal and obtained the proteins with remarkably red-shifted absorbance and fluorescence spectra. This result demonstrates that chromophore replacement is promising strategy for modulating the spectral and voltage properties for more sensitive action potential detection. In the third Chapter, we describe our attempts to extend the fluorescence modulation strategy to “empty” fluorescent protein barrels, by replacing the endogenous chromophore with a synthetic version (HBDI). We expect that a chromophore replacement strategy could help provide new imaging tools with improved fluorescent properties. We performed some modifications on FP barrels with the aim of allowing the synthetic chromophore to insert into the empty barrel. Unfortunately, we could not obtain any improvements on fluorescent properties of FPs by this strategy
Development of Ir- and Rh-Catalyzed Deoxygenation and Carbene Cross Coupling Reactions of Allylic Carbonates
No full textTransition metal-catalyzed allylic substitution reactions are widely used for the selective formation of new bonds. This class of reaction has been extensively studied with a variety of nucleophiles and under optimized conditions that will furnish product in high yield and with high chemo-, regio- and enantioselectivity. However, there remain opportunities for established catalyst systems to facilitate new transformations through the interception of metal π-allyl complexes with novel partners. This thesis describes two reactions of transition metal π-allyl species. The selective deoxygenation of alcohols is a persistent challenge in organic synthesis and a host of methods have been developed to address this problem. The use of [Ir(COD)Cl]2 (COD = 1,5 cyclooctadiene) and [Rh(COD)Cl]2 precatalysts in the presence of a diazene transfer agent, N-isopropylidene-N’-2-nitrobenzenesulfonyl hydrazine (IPNBSH), facilitated the reductive transposition of allylic carbonates with high regioselectivity and good to excellent yield. The reaction proceeded under mild conditions and was highly chemoselective. [Ir(COD)Cl]2 was effective for the deoxygenation of both alkyl and aryl monosubstituted allylic carbonates, including substituents potentially susceptible to decomposition by the transition metal. 1,3-Disubstituted allylic carbonates, including α,β–unsaturated esters, were reduced by [Rh(COD)Cl]2 and P(OPh)3. Interception of a π-allyl fragment by a diazo-generated carbene intermediate gave the net cross coupling 1,3-dieneoate products in good yield, and in some cases, with high selectivity for the thermodynamically disfavored E,Z isomer. Only a single, Ir precatalyst, which has not previously been reported to interact with diazo compounds, gave acceptable yield of product. This observation potentially represents a new mode of activity for a well understood catalyst system
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