Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 95 for “"Diastereoselectivity"”.
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Diastereoselectivity of Organometallic Additions to Nitrones
Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs
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Diastereoselectivity of the metallo-enamine condensation; addition and cyclization reactions of vinyl isocyanates
The diastereoselectivity of the metallo-enamine condensation was examined using a variety of imines and aldehydes. The highest selectivity (5:95, anti:syn) was observed in the reaction of the lithium enamine of propylidene-t-butylamine with pivaldehyde. Therefore, high diastereoselectivities can be …
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Mechanistic studies of diastereoselective cyclopropanations of homochiral ene-ketals and synthesis and resolution of diastereomeric alpha-hydroxycycloalkanone ketals.
… model was formulated to explain the observed diastereoselectivity seen for the common ring systems. Diastereoselectivity is thought to result from preferential chelation of the Simmons-Smith reagent at the least sterically hindered lone pair of electrons on the dioxolane oxygen proximal to the …
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Stereoselective carbon-carbon bond forming reactions using chiral phosphorus(V) compounds and the derived anions
… varying N-alkyl and P-alkyl substituents. High diastereoselectivity was achieved with N-neopentyl substrates (up to 92:8 diastereoselectivity).
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Borylations and Silylations of Alkenyl and Alkynyl Carbonyl Compounds Employing a Mild and Environmentally Friendly Cu(II) Catalyst
… of the electron withdrawing group controlled diastereoselectivity. Esters and amides exclusively form E-product, while aldehydes and ketones favor Z-product. Mechanistic insights into the catalytic cycle as well as origin of diastereoselectivity are discussed.
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Tandem Cycloaddition Chemistry of Nitroalkenes: Total Synthesis of (+)-1-Epiaustraline and Synthesis of the Pentacyclic Core of (+/-)-Scandine
… proceeded with high chemical yield and modest diastereoselectivity to provide an advanced bicyclic intermediate. Construction of two of the remaining three rings was accomplished by an intramolecular Heck cyclization of a pendant aryl iodide. This process proceeded with high …
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Chiral phosphonyl and thiophosphonyl carbanions in asymmetric alkylation and olefination reactions
… l-series, the methylation proceeded with high diastereoselectivity (90/10-97/3) and the benzylation selectivity ranged from 80/20 to 94/6. In the u-series, little steric influence on the methyl selectivity (83/17-85/15) was observed except in the case of sterically demanding group (R = $\rm …
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Studies in Asymmetric Catalysis: Lewis Base Catalyzed, Enantioselective Addition of Trimethylsilyl Cyanide, Trimethylsilyltrifluoromethane, and Glycolate-Derived Silyl Ketene Acetals to Aldehydes
… alpha,beta-dihydroxy esters with high syn-diastereoselectivity, whereas the tert-butyldimethylsilyl ketene acetals derived from bulky esters of alpha-methoxy acetic acid provide enantiomerically enriched alpha,beta-dihydroxy esters with high anti-diastereoselecitvity. The observed …
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Phosphorus-Stabilized, Carbanion-Accelerated Claisen Rearrangements: Asymmetric Induction via 1,3,2-Oxazaphosphorinanes
… explained in terms of both internal and relative diastereoselectivity. The sense of asymmetric induction is established by degradation of the Claisen rearrangement products to ($R$)- and ($S$)-dimethyl methylsuccinates. Two limiting transition state models are proposed to rationalize the high …
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NATURAL PRODUCT INSPIRED METHODOLOGIES: ADVANCES IN DIASTEREOSELECTIVE N-SULFINYL IMINE AND TRIFLUOROPYRUVIC ACID REACTIONS
… and ketimines with 50-99% yield and 3:1 to 98:2 diastereoselectivity. A one-pot protocol was developed to access 1,2 amino alcohols with high diastereoselectivity. With a good understanding of the diastereoselective reaction with NSMD and NSMEs, I joined with Dr. Po-Cheng Yu to develop a highly …
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Chemistry with chiral lithium amides: enantiotopic group and face-selective reactions
… ketal and benzaldehyde demonstrated the high diastereoselectivity (up to 98% de) and the moderate to high enantioselectivity (up to 75% ee) induced by those chiral lithium amides. On the other hand, high diastereoselectivity (up to 100% de) and the low enantioselectivity were obtained from the …
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Investigation of metal mediated reactions for natural product synthesis
… the role that solvent can have upon the diastereoselectivity of ether-directed rearrangements. In addition to this, a novel tandem aza-Claisen rearrangement and ring closing metathesis reaction has been developed. This reaction allows the synthesis of cyclic allylic trichloroacetamides in …
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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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Diastereoselective acylation of trans-2-substituted-cyclohexanols and glycosidase inhibition studies
… some substituents (RX) may completely invert its diastereoselectivity. These observations have been rationalized in terms of a stereoselective intramolecular assistance by the RX group to the acylation of the neighboring hydroxyl ("bait-and-hook" mechanism). A series of trans …
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Synthesis of novel heterocyclic α-amino acids
… was found to be moderate (10-87%) due to poor diastereoselectivity in the key alkylation step. Moreover, the strict experimental conditions required for the alkylation reaction were found to be difficult to reproduce. Attempts to apply this enolate anion strategy to the incorporation of nucleic …
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METHODOLOGY DEVELOPMENT OF N-SULFINYL METALLOENAMINES AND ASYMMETRIC TOTAL SYNTHESIS OF (+)-EPIIBOGAMINE
… total synthesis of (−)-albocycline. However, the diastereoselectivity of this reaction was found to be incorrectly reported. Mosher ester analysis and HPLC analysis with a chiral column were employed to determine the dr. The vinylogous aldol reaction was optimized. Studies on the mechanisms …
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Accelerating process development of complex chemical reactions
… produce a chiral γ-lactam, with conversion and diastereoselectivity as objectives. We adapted a state-of-the-art multi-objective machine learning algorithm, based on Gaussian processes, to utilise the descriptors as inputs, and to create a surrogate model for each objective. The aim of the …
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A study of alkylation reactions α- to nitrogen for application in alkaloid synthesis
… acid. The radical cyclisation occurred with good diastereoselectivity, to afford of the four possible diastereomers, a major product(~ 50%) with the hydrogens of the two new stereocentres in a cis relationship. Similarly the carbanionic cyclisation gave a major product in even higher …
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Studies directed towards the total synthesis of (+)-sieboldine A
… natural product in good yield and with excellent diastereoselectivity about the newly formed tertiary allylic alcohol ... The hydrindane product from this reductive cyclization can be transformed into the tetracyclic N,O-acetal which is two steps removed from the natural product 1. Efforts …
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