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Showing 1 to 20 of 32 for “"asymmetric induction"”.
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Asymmetric induction in solid state photochemistry
… Photolysis of the chiral crystals resulted in asymmetric induction in the products. The regioselectivity of the photorearrangements of the starting materials prior to salt formation was studied in solution as well as in the solid state. In addition, the photochemistry of the methyl and ethyl …
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Phosphorus-Stabilized, Carbanion-Accelerated Claisen Rearrangements: Asymmetric Induction via 1,3,2-Oxazaphosphorinanes
… Most importantly, the first examples of asymmetric induction in the Claisen rearrangement with chiral phosphorus anion-stabilizing groups are documented. The observed asymmetric induction, which is highly dependent on the metal counterion involved, is explained in terms of both internal …
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Mechanistic studies of asymmetric induction at benzylic centers of organolithium species
The mechanisms of asymmetric induction involving the lithiation and substitution of N-benzyl-N-Boc-N-p-methodically amine and N-benzyl-N-Boc-N-3-chloropropyl amine were investigated and are reported here. These two substrates undergo deprotonation with butyllithium in the presence of the chiral …
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Intermolecular and intramolecular asymmetric induction at the beta-benzylic position of carboxamides in directed lithiation-substitution sequences
Asymmetric induction at the $\beta$-benzylic position of secondary carboxamides in directed lithiation-substitution reactions has been achieved intermolecularly by using ($-$)-sparteine as the external chiral ligand and intramolecularly by using $\alpha$-methylbenzylamine as the covalently attached …
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Remote asymmetric induction in the organocatalytic azaDarzens synthesis of peptide aziridines: towards the assembly of new glycopeptide antibiotic analogues
… chapter describes the development of an asymmetric organocatalytic aza-Darzens aziridination protocol using diazopeptides and amino acid imines as substrates. A structurally diverse range of peptide aziridines are reported in yields and diastereoselectivity of up to 99%. It is anticipated …
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Computational study on the origins of asymmetric induction in Pd-catalyzed cross-coupling reactions and suggestions for improvements thereupon
The origins of asymmetric induction in the Suzuki-Miyaura cross coupling reaction are investigated computationally with density functional theory. Monophosphine-bound palladium complexes are analyzed in the context of oxidative addition to aryl halides, and ligands are explored in terms of steric …
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Synthesis and utilization of guanidine catalysts for applications directed towards the preparation of butenolide and modified amino acid derivatives
… an overall yield of30%. Attempts to increase asymmetric induction were focused on incorporation of axial chirality to the (R)phenylalaninol catalyst using binaphthyl diamine. Incorporation of (S)-binaphthyl exhibited destructive selectivity, whereas incorporation of (R)-binaphthyl demonstrated …
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Water Soluble Phosphines, Their Transitional Metal Complexes, and Catalysts
… phosphine analog. Finally, homogeneous asymmetric hydrogenation was carried out in the presence of a chiral surfactant in an attempt to affect asymmetric induction. The catalytic results showed that at a surfactant/Rh ratio of 25, the asymmetric hydrogenation of AACA-Me …
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Explorations with optically active, cage-annulated crown ethers.
… Michael addition was studied. The extent of asymmetric induction, expressed in terms of the enantiomeric excess (%ee), was monitored by measuring the optical rotation of the product and comparing to the literature value.
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Organocatalysts for the asymmetric reduction of aromatic ketimines with trichlorosilane
Asymmetric reduction of N-aryl ketimines 189a j, 212, and 213 with trichlorosilane can be catalyzed by new N-methyl L-amino acid-derived Lewis-basic organocatalysts, such as bisamide 197c (10 mol%), in toluene at room temperature with high enantioselectivity (≤92% ee). The structure-reactivity …
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Nitroalkene (4+2) cycloadditions of achiral and chiral vinyl ethers. The stereochemical consequence of the Lewis acid promoter and studies toward the total synthesis of (+)-pretazettine
… have been found to provide high levels of asymmetric induction in tandem inter (4+2) /intra (3+2) nitroalkene cycloadditions. Either enantiomeric series of tandem cycloaddition/hydrogenolysis product is available from the chiral auxiliary of a single absolute configuration by judicious …
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ASYMMETRIC REDUCTIONS BY CHIRAL LITHIUM-ALUMINUM HYDRIDE AND POTASSIUM-BOROHYDRIDE REAGENTS
… 77%ee(R), respectively}. A general additivity of asymmetric induction due to the chiral centers in the carbinol and noncarbinol arms of the ligands was perceived, with 7 optimizing the inductive influences. The direction of the asymmetric induction was rationalized by means of a stereocorrelation …
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Capillary Electrophoretic Separation of Sulfoxides
Chiral sulfoxides are most widely used in asymmetric synthesis. Their application as chiral synthons has now become a well-established and reliable strategy, mainly due to availability and high asymmetric induction exerted by the chiral sulfinyl group. Very few articles have been published on the …
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Vinylcyclopropanation of enones in [2+3] cyclopentene annulation: application to the total synthesis of (-)-retigeranic acid
… were also investigated. The possibility of asymmetric induction utilizing (-)-menthyl 2-bromocrotonate (169) was briefly investigated. An application of this methodology was expressed in the total synthesis of (-)- retigeranic acid (1), achieved in fifteen steps from menthene (187) in a …
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Palladium (II) / sulfoxide - promoted strategies for efficient and selective allylic C-H oxidations
… required a different approach toward achieving asymmetric catalysis. Critical to the success of this goal was the development and utilization of a novel chiral aryl sulfoxide-oxazoline (ArSOX) ligand. We have reported the enantioselective synthesis of isochromans via Pd(II)-catalyzed allylic C–H …
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New oxy-dihydrofuran annulation methodology
… have been investigated. The possibility of asymmetric induction using chiral auxiliaries located either at the ester site or at the r- position of 11 was addressed. A new oxydihydrofuran annulation methodology was developed following the above investigation. The addition of the lithium …
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The study of the asymmetric synthesis of lignans
The work in this thesis focuses on the asymmetric synthesis of lignans by approaches such as Diels-Alder reactions, asymmetric alkylation reactions, and intramolecular oxidative coupling reactions. In addition to developing asymmetric synthetic methodologies for chiral lignans, an investigation of …
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Synthesis of pyrrolizidine diols via azide-diene cycloadditions
… 8, 9, 10, and 11. The possibility of asymmetric induction was also investigated, and was realized in the microbial reduction of only one of the enantiomers of alcohol ill protected as ester 248, providing potential access to either enantiomeric series of pyrrolizidine diols. [see …
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IMPROVING THE SCOPE AND UNDERSTANDING OF THE SYMMETRIC AND ASYMMETRIC SUZUKI COUPLING REACTION
Investigations into the Symmetric and Asymmetric Suzuki cross-coupling reaction have been described. A new reaction protocol has been developed in which isolated pre-activated sodium trihydroxyarylborate salts were employed as the organoboron coupling partner, resulting in a more convenient and …
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