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Showing 1 to 20 of 44 for “"chiral auxiliary"”.
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A new cyclohexyl-based chiral auxiliary: application in the total synthesis of (+)-linalool oxide
Seven different racemic cyclohexyl-based chiral auxiliaries (2.4-2.10) were synthesised in moderate to good yields (38-85%) by nucleophilic opening of cyclohexene oxide using carbanions. The racemic cyclohexyl-based chiral auxiliaries were coupled with the 6-methyl-2- methylenehept-5-enoyl chloride …
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Radical cyclisation studies of chiral α-acylamino radicals : a model study towards Tacaman indole alkaloid synthesis
he radical cyclisation of chiral 4,5-substituted N-acyl-2-aza-6-heptenyl radicals, derived from D-ribose, has been undertaken as a model stuay towards Tacaman indole alkaloid synthesis. The radical cyclisations were conducted using tributyltin hydride/AIBN in refluxing benzene. The α-acylamino …
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Enantioselective Conjugate Additions to a Hindered Cyclohexenone System
… that steric congestion around the enone from the chiral auxiliary and the vicinal quaternary carbon contributed to these difficulties. Because our lab has previously reported on ring forming intramolecular conjugate addition reactions with oxygen,<sup>1</sup> nitrogen,<sup>2</sup> and …
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Intermolecular and intramolecular asymmetric induction at the beta-benzylic position of carboxamides in directed lithiation-substitution sequences
… by using ($-$)-sparteine as the external chiral ligand and intramolecularly by using $\alpha$-methylbenzylamine as the covalently attached chiral auxiliary.
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Induced pi-facial discrimination in the alkylation of chiral derivatives of glycine.
… of increasing pi-character. When the chiral auxiliary contained a naphthyl group the stereoselectivity was >80% for every electrophile used. Part B. The alkylation of the trans 2-phenylcyclohexylamide of methyl glycinate with a series of electrophiles was examined. Incorporation of the …
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S(N)2' reactions of chiral allylic carbamates with organocopper reagents. Asymmetric synthesis of tertiary and quarternary carbon centers
The chiral auxiliary-based, asymmetric S$\sb{\rm N}2\sp\prime$ cuprate reactions of allylic carbamates were examined. The amine and amino ether auxiliaries were evaluated based on the enantioselectivities each provided in the reactions of the carbamates with methylcopper. The effects of varying the …
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Enantioselektive Pi-Komplexierung durch intramolekulare Chiralitätsübertragung aus CpTi-Aminosäure-Komplexen
This work contains new synthesis of chiral CpTiL*-complexes where L* = amino acid, lactic acid or phenylethylamine. With these complexes the possibility for the preparation of enantiomerically enriched "titanocenes" [CpCppcTiCl2], where Cppc is a prochiral cyclopentadienide, was explored. In …
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Asymmetrische Synthese ausgehend von allylischen Sulfoximinen: neuartige Gamma-Aminosäuren und cyclische Aminosulfoxonium Ylide
… degradation of a furan ring. The employed chiral auxiliary (S)-N,S-dimethyl-S-phenylsulfoximine could be recovered as a sulfinamide isolated in enantiomerically pure form. There are literature known methods for its transformation into the starting chiral auxiliary. Moreover a new one step …
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Stereoselective carbon-carbon bond forming reactions using chiral phosphorus(V) compounds and the derived anions
… carbon-carbon bond forming reactions using chiral auxiliary-based phosphorus reagents. The general utility of these diamines as chiral auxiliaries in the diastereoselective alkylation of P-alkyl anions was examined. A systematic study of the alkylation of the P-alkyl anions was accomplished …
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Asymmetric synthesis of sultones and sulfonic acid derivatives
… 5,6-di-O-isopropylidene-alpha-D-allofuranose as a chiral auxiliary has been developed. High asymmetric inductions of the alpha-allylations were achieved along with good to excellent yields. In all cases the diastereomerically pure allylated sulfonates could be obtained by recrystallization (de = …
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[3+2]-Cycloadditions of Azomethine Imines and Ynolates and Progress Towards a Radical Three-Component Cross-Coupling Reaction
… example in which the azomethine imine acts as a chiral auxiliary to control the cycloaddition. Optically active azomethine imines yield bicyclic pyrazolidinones in high yields, and conditions for removal of the azomethine imine chiral auxiliary have been defined to yield optically active …
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Asymmetrische Synthese von Gamma-Hydroxy-Alpha-Aminosäuren, 1,3-Aminoalkoholen und 2-Amino-3-Phosphonopropionsäure
… protection, 1,2-addition and cleavage of the chiral auxiliary the products could be isolated over five steps in 30 to 54% overall yield and diastereomeric excesses of 78 to 84% and enantiomeric excesses over 96%. Furthermore we developed a hydrazone Strecker-method for the asymmetric synthesis …
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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
Chiral enol ether dienophiles derived from (1R,2S)-($-$)-2-phenylcyclohexanol and (R)-($-$)-2,2-diphenylcyclopentanol (($-$)-6 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 …
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Asymmetric cyclopropanation via catalysts incorporating the 1,4-diol ligands and the newly designed dioxaborolane /
… new methodology for the asymmetric synthesis of chiral organic compounds is a major focus in modem organic chemistry. The use of chiral catalysts is replacing chiral auxiliaries as a new tool for synthetic chemists. An efficient chiral catalyst allows for large quantities of optically active …
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Towards the Total Synthesis of Antascomicin B. Efforts to Construct the C1-C21 Fragment
… uses inexpensive (S)-α-methylbenzylamine as the chiral auxiliary. The allylic amide underwent rearrangement to establish the C14 and C15 stereocenters in high yield and good diastereoselectivity. We found a surprisingly high yielding acid mediated lactonization that was employed to cleave the …
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Delta-Hydroxy-beta,beta-disubstituierte-beta-Aminosäuren: asymmetrische Synthese und Überführung in Dipeptide
… point of the seven step synthesis is the chiral auxiliary N,S-dimethyl-N-phenylsulfoximine, which is reacted with aldehydes or ketones to give allylic sulfoximines. The latter ones were gamma-hydroxylated using aldehydes, thus giving access to the two new stereogenic centers containing …
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New routes to enantioenriched substances through small organic molecules
… a set of acids and an oxazolidinone as the chiral auxiliary. The inter- and intramolecular cycloaddition of in situ-generated keteniminium salts gives bicycles with a good enantioselection. A key intermediate of Iloprost, a chemically stable and biologically active mimic of prostacyclin PGI2 …
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Synthesis of [beta]-heteroaryl propionates via trapping of carbocations with [pi]-nucleophiles, efforts towards the total synthesis of acutumine, and the design, synthesis, and thermodynamics of protein-ligand interactions at the Src SH2 domain
… diastereoselectivity was also achieved when a chiral auxiliary was incorporated into the [pi]-nucleophile. Progress towards the synthesis of acutumine, an alkaloid possessing a densely functionalized aza-propellane core, two quaternary centers, and a neopentylic chlorine atom, was pursued. A …
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Dynamics and Catalytic Resolution of Selected Chiral Organolithiums
… using stoichiometric amounts of the chiral ligand. When this concept is implemented successfully, it obviates the need for covalently attached chiral auxiliary based methods, asymmetric deprotonation, and asymmetric synthesis of a precursor stannane as ways to access enantioenriched …
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Diastereoselective Synthesis of Planar Chiral N-Substituted Ferrocenes Derived from Epimeric Imidazolones and their Application to Asymmetric Hydrogenation of Quinolines
… ferrocene bearing 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 …
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