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Showing 1 to 20 of 114 for “"Stereoselectivity"”.
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Stereoselectivity, kinetics, and engineering of flavin/deazaflavin oxidoreductases for use in industrial biocatalysis
… complex structures and/or a high degree of stereoselectivity, which are often technically challenging in chemosynthesis, find relevance in biocatalysis. Moreover, traditional chemical synthesis continues to face concerns about environmental costs and viability. Biocatalysts, such as enzymes, …
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Stereoselectivity, kinetics, and engineering of flavin/deazaflavin oxidoreductases for use in industrial biocatalysis
… complex structures and/or a high degree of stereoselectivity, which are often technically challenging in chemosynthesis, find relevance in biocatalysis. Moreover, traditional chemical synthesis continues to face concerns about environmental costs and viability. Biocatalysts, such as enzymes, …
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Beta-lithiations of carboxamides: An investigation of the regio- and stereoselectivity of directed lithiations
… metalation has been found to occur with high diastereoselectivity and the resulting carbanion is best described as a pyramidal benzyllithium species based on $\sp{13}$C NMR evidence.
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Transition Metal Heterogeneous Catalysis Towards Applications in Sustainable Energy: Leveraging Rational Design Principles for Activity, Stability, and Stereoselectivity
… rates per active site, however with a notable stereoselectivity toward cis-decalin across compared to the other Ni catalysts. This work highlights Ni-MHOFs as precursors for transition metal catalysts that emulate the stereoselectivity of NM catalysts, thereby reducing energy requirements in …
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The development of directing group enabled hydroamination strategies to access to 1,2-, 1,3-, and 1,4- diamines with high levels of regio-, chemo-, and stereoselectivity
… In the case of cyclic olefins, high diastereoselectivity is observed. This strategy has multiple interesting future directions, including potential enantioselective hydroamination of internal olefins, use of different nucleophiles, and comprehensive mechanistic studies.
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Induced pi-facial discrimination in the alkylation of chiral derivatives of glycine.
… of electrophiles was examined. The reaction stereoselectivity varied from 46 to 81% depending on the steric and electronic nature of the electrophile when (Ar = phenyl). Higher stereoselectivity was observed when reacting electrophiles of increasing pi-character. When the chiral auxiliary …
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Stereoselective reactions of 16-Methylene 19-Norsteroids
… occurred in good yields, but poor stereoselectivity was obtained due to mechanistic considerations. Poor stereoselectivity was also obtained for the peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-ol, due to the pseudo-equatorial position of the 17β-hydroxyl …
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Application of Density Functional Theory to Study the Mechanism of Alkali Metal Enolate Oxidation by N-sulfonyloxaziridines, Umpolung Amide Synthesis from Halo-Amino-Nitro Alkanes, Alkali-Metal Catalyzed Transfer Hydrogenation of Ketones, and Asymmetric Catalyzed Aza-Henry Reactions
… reaction mechanisms and the factors governing stereoselectivity. To illustrate the versatility of DFT methods, the following reactions were studied: (1) Li+, Na+, and K+ enolate addition to chiral N-sulfonyloxaziridines, stereoselectivity was found to be controlled by enolate, sulfonyl, and …
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Silicon-Directed Nazarov Cyclization: Stereochemical, Mechanistic, and Substituent-Compatibility Studies
… The cyclization proceeds with good to excellent stereoselectivity in cyclohexenyl systems bearing a variety of ring substituents. In all cases the trans family of isomers predominates; cis ring-fused products are formed almost exclusively. The stereoselectivity is high ($>$9:1) with bulky …
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Radical cyclisation studies of chiral α-acylamino radicals : a model study towards Tacaman indole alkaloid synthesis
… as chiral auxiliary showed excellent regio- and stereoselectivity. Out of a possible 4 diastereomers, only two were obtained in a 2:8 ratio. It was established that the isopropylidene ketal directed the cyclisation stereoselectively and that no stereoselectivity was observed in the absence of the …
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Intramolecular (4+2) -Cycloadditions of Three Heterodienes: Nitrosoalkenes, Nitroalkenes, and Z-Alpha,beta-Unsaturated Aldehydes
… sulfides at ambient temperature. The yield and stereoselectivity of the tricyclic octahydronaphthalene (6-6)- and hexahydroindene (6-5)-oxazine cycloadducts varied. In the enol ether cases, the success of the cycloaddition depended on the olefin geometry. Only the dienophile bearing the proper …
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Combined Application of Density Functional Theory and Molecular Mechanics Sampling Techniques to study Chemical Systems, from Intramolecular Rearrangements to Polymerization Reactions
… these catalysts, including the origin of their stereoselectivity, the mechanism of the inversion of catalyst chirality, and the relative stereoselectivity of the catalysts in the initiation stage, and the mechanism of stereoselectivity in the propagation stage, were described.
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Synthesis and Claisen Rearrangement of Alpha-Ethoxyallyl Vinyl Ethers. Evidence for a Dipolar Transition State
The product stereoselectivity, scope, and mechanism of the Claisen-Micheal reaction (8 $\rightarrow$ 11) were explored. The products (e.g. 11) of the Claisen-Micheal reaction, which are enol ethers, are protected equivalents of the adducts obtained from the Micheal reaction of $\alpha,\beta$-enals …
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Asymmetric synthesis of novel anthracyclinones
… of the dioxane (30) proceeded with excellent stereoselectivity to give an 82% yield of the diastereomerically pure chlorotetracycle (78). Stronger Lewis acids gave poorer selectivity and boron trifluoride etherate reacted slowly with (30) but with high selectivity to give the …
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Studies on the Total Synthesis of (+/-)-Cameroonan-7alpha-Ol and Presilphiperfolan-8-Ol and Discovery of a Novel Stereoselective Prins Cyclization of Delta,epsilon-Unsaturated Ketones
… evidence for substrate generality while the stereoselectivity was rationalized by intramolecular delivery of the nucleophile.
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Boron-Mediated Semireduction of Alkynoic Acid Derivatives
… metals and often results in incomplete (E)-stereoselectivity. This dissertation describes three novel uses of a diboron reagent or pinacolborane that reduce propiolic acid derivates selectively to (E)-alkenes and one method that installs pinacolatoboron yielding exclusively …
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2-Silicon-Substituted 1,3-Dienes: Participants in Diels-Alder Chemistry and Metal-Mediated Processes
… these processes include poor efficiency and poor stereoselectivity. My dissertation research has centered around the synthesis and use of 2-silicon-substituted 1,3-dienes to alleviate these problems. These dienes, whether utilized as reagents or intermediates, serve as synthons for less …
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A study of activated ketal reduction with borane dimenthyl sulphide
… of approaches accomplishing a high degree of stereoselectivity have been developed. This thesis describes a study of a novel reagent combination, namely borane dimethyl sulphide and trimethylsilyl trifluoromrthanesulphonate (TMSOTf) for reductive ketal cleavage.
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Towards the synthesis of hyacinthacines
… cases CS-symmetrical dioxanones offer a better stereoselectivity. A new approach towards synthesis of hyacinthacine alkaloids: 2-epihyacinthacine A2, 3-epihyacinthacine A2 and their enantiomers is illustrated. The key step involves an organocatalytic aldol reaction of dioxanones where proline is …
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