Global ETD Search
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Showing 1 to 20 of 91 for “"diastereoselective"”.
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Diastereoselective α-Alkylation of Chiral β-Borylated Esters
… This thesis reports the development of a novel diastereoselective reaction for the α-alkylation of chiral β-borylated esters. We propose that standard deprotonation of chiral β-borylated esters with lithium diisopropylamide (LDA) leads to the formation of a boron"ate" intermediate that upon …
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Diastereoselective acylation of trans-2-substituted-cyclohexanols and glycosidase inhibition studies
… and trans -2-substituted-cyclohexanols proceeds diastereoselectively, i.e. produces mixtures of unequal amounts of diastereomers. We found for the first time that addition of pyridine or diisopropylethylamine accelerates the acylation, and unexpectedly for some substituents (RX) may completely …
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Diastereoselective aza-cope rearrangement-mannich cyclizations of conformationally mobile iminium cations
<p>We have developed a Lewis-acid catalyzed, diastereoselective aza-Cope rearrangement— Mannich cyclization (ACM) to form acyl pyrrolidines from conformationally mobile substrates. Earlier studies from our lab have shown that substituted acyl pyrrolidines can be synthesized with …
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NATURAL PRODUCT INSPIRED METHODOLOGIES: ADVANCES IN DIASTEREOSELECTIVE N-SULFINYL IMINE AND TRIFLUOROPYRUVIC ACID REACTIONS
… products. In 2017, our first report of a novel diastereoselective hydroxylation protocol for metallodienamine (with 4:1 dr) in concise 14-step synthesis of (−)-albocycline warranted further exploration of the method. By screening different metal bases, I was able to observe a unique …
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Nucleophilic Addition to Azoalkenes; Diastereoselective Synthesis of β-Hydroxy Ketones and β,γ-Fused γ-Lactams
The α-alkylation of ketones and their derivatives by the addition of their corresponding enolates to alkyl halides is a fundamental synthetic transformation, but its utility is limited because the key bond-forming step proceeds in a bimolecular nucleophilic substitution fashion. Here in the first …
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Advancements in the diastereoselective synthesis of acyl pyrrolidines via the tandem aza-Cope—Mannich cyclization pathway
<p>We have developed a Lewis-acid catalyzed, diastereoselective aza-Cope rearrangement— Mannich cyclization to form acyl pyrrolidines from conformationally mobile substrates. In earlier studies from our lab, Brønsted acid-catalyzed reactions to form the same acyl pyrrolidines resulted in …
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Diastereoselective nickel-catalyzed reductive coupling of alkynes and aldehydes and application towards the B-type amphidinolides
… viable means for their total construction. The diastereoselective nickel-catalyzed reductive coupling of simple aryl-substituted alkynes and a-oxyaldehydes was developed and applied to the construction of the C15-C26 region of amphidinolide H3. ... Alternatively, the nickel-catalyzed reductive …
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Mechanistic studies of diastereoselective cyclopropanations of homochiral ene-ketals and synthesis and resolution of diastereomeric alpha-hydroxycycloalkanone ketals.
A series of homochiral ene ketals were prepared and subjected to the Simmons-Smith cyclopropanation. A mechanistic model was formulated to explain the observed diastereoselectivity seen for the common ring systems. Diastereoselectivity is thought to result from preferential chelation of the …
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Diastereoselective Synthesis of Planar Chiral N-Substituted Ferrocenes Derived from Epimeric Imidazolones and their Application to Asymmetric Hydrogenation of Quinolines
… a proline-derived chiral directing group and diastereoselective lithiation-electrophile quench of the pro-Sp hydrogen of the ferrocene to give planar chiral products in >95:5 dr. The auxiliary group is found to be stable to lithium bases of types RLi and R2NLi giving the same …
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Diastereoselective Lithiation-Substitution of N-Silyl-Protected-(S)-Tetrahydro-1H-pyrrolo[1,2-c]imidazole-3(2H)-ones and Applications of Their Derivatives
… with an N-triethylsilyl group that undergoes diastereoselective lithiation followed by electrophile quench to give C5-substituted products with syn stereochemistry. The N-silylated derivatives may be more easily N-deprotected as compared to previous N-t-Bu analogues to give secondary ureas. …
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Diastereoselective Lithiation-Substitution of N-Silyl-Protected-(S)-Tetrahydro-1H-pyrrolo[1,2-c]imidazole-3(2H)-ones and Applications of Their Derivatives
… with an N-triethylsilyl group that undergoes diastereoselective lithiation followed by electrophile quench to give C5-substituted products with syn stereochemistry. The N-silylated derivatives may be more easily N-deprotected as compared to previous N-t-Bu analogues to give secondary ureas. …
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Total syntheses of (±)-dracephalone A and (±)-dracocequinones A and B, progress towards a total synthesis of cassiabudanols A and B, and synthetic studies towards total synthesis of N-oxy-diketopiperazine containing natural products.
… Lewis acid-mediated spirocyclization in a highly diastereoselective fashion. Subsequent trans-decalin formation and a late-stage Suárez oxidation constructed the [3.2.1] oxabicylic core that led to the completion of (±)-dracocephalone A in 10 steps and 8% overall yield from known materials. …
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Development of a Diastereoselective [4+2]-Annulation of Vinyl Carbodiimides With Chiral N-Alkyl Imines and Its Application to the Synthesis of the Batzelladine Alkaloids: Total Synthesis of (+)-Batzelladine a and (-)-Batzelladine D
A diastereoselective [4+2] annulation of vinyl carbodiimides with chiral N-alkyl imines has been developed to access the stereochemically rich anti-fused polycyclic guanidine cores of the batzelladine alkaloids. Application of this strategy, together with additional key steps such as a long-range …
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I The synthesis of papyracillic acids: Application of the tandem chain extension-acylation reaction II Diastereoselective synthesis of beta-methyl-gamma-keto esters through the utility of an L-serine auxiliary
… and stereochemical reassignment.</p><p>Diastereoselective syntheses of beta-methyl-gamma-keto esters were achieved through the utility of an L-serine auxiliary. Preparation of a series of L-serine derived precursors were prepared and studied.</p>
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Asymmetric synthesis of amines and amine derivatives: I. The cerium-mediated diastereoselective addition of organometallic reagents to chiral pyrrolidine hydrazones. II. The enantioselective addition of organolithium reagents to imines and hydrazones
Two conceptually different approaches to the asymmetric synthesis of amines and amine derivatives via the addition of organometallic reagents to the carbon-nitrogen double bond of azomethines has been investigated.
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Beta-lithiations of carboxamides: An investigation of the regio- and stereoselectivity of directed lithiations
An investigation of the diastereoselective $\beta$-metalation and of the structure of a carbanion of a $\beta$-phenyl tertiary amide has been carried out. The directed metalation has been found to occur with high diastereoselectivity and the resulting carbanion is best described as a pyramidal …
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Syntheses of C-glycoside natural products via oxocarbenium cationic intermediates
… antibiotic (+)-bruguierol C. The key step is the diastereoselective capture of an in situ generated oxocarbenium cation via an intramolecular Marson-type Friedel-Crafts cyclization, which concomitantly generates the chiral quaternary center. The third chapter illustrates the formal syntheses of …
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Viridiofungins and xeniolide F: target oriented synthesis using different rearrangement reactions of a common substrate class
… The [2,3]-Wittig rearrangement allowed the diastereoselective synthesis of the polar head group with two adjacent stereogenic centers. The E-configured double bond was formed by a Julia-Kocienski olefination. During the studies toward the total synthesis of xeniolide F a new, …
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