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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Developing novel synthetic methods for the Pauson Khand reaction

Blunt, Gillian January 2002 (has links)
No description available.
2

Solution and solid-phase amine N-oxide promoters for use in metal-mediated organic synthesis

Ratcliffe, Paul David January 2003 (has links)
No description available.
3

Utilisation of organocobalt, organochromium and organophosphorus complexes in synthesis

Caldwell, John J. January 2000 (has links)
No description available.
4

Studies on selectivity in the Pauson-Khand reaction and synthesis of an intermediate of isocarbacyclin

Meyer, Todd Roland. January 2005 (has links) (PDF)
Thesis (Ph. D)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: Tom Livinghouse. Includes bibliographical references (leaves 138-144).
5

Coordination Chemistry of Bis(diphenylphosphino)amine Ligands with Cobalt Carbonyl and the Intermolecular Catalyzed Pauson-Khand Reaction

Merrill, James Malcolm 11 January 2002 (has links)
Bis(diphenylphosphino)amine (PNP) ligands, prepared from (S)-(-)-1-methylbenzyl amine, (-)-cis-myrtanylamine, (S)-(-)-1,1-napthyl(ethyl)amine (PNP1 1a, PNP2 1b, and PNP3 1c respectively) and their cobalt carbonyl complexes are reported. In the absence of alkynes the PNP ligands chelate to the cobalt rather than bridging the two cobalt centers. Although the PNP ligands are chiral the crystal structures are best solved in centrosymmetric space groups with disorder at the chiral carbon with the exception of (PNP3)Co2(CO)6, 2c, which is solved in a non-centrosymmetric space group. When the PNP ligand chelates to cobalt, as in 2, the compounds show activity for the catalytic Pauson-Khand reaction, whereas when the PNP ligand bridges, as in 3, the reaction precedes stiochiometrically. The use of these chiral ligands has not yet resulted in enantioselective catalytic Pauson-Khand cycloadditions. However, a small 15% e.e. was detected for the stiochiometric Pauson-Khand cycloaddition with 3c as the metal substrate. / Master of Science
6

Tandem Reactions Involving Ruthenium Alkylidenes

Finnegan, David Francis January 2009 (has links)
Thesis advisor: Marc L. Snapper / Tandem Reactions have proven themselves to be useful reactions for the synthesis of highly complex materials. Ruthenium alkylidenes are shown to be useful precursors for the development of new tandem processes. First, a new tandem metathesis/hetero-Pauson-Khand process is developed using Grubbs' second generation catalyst. Next, various metatheis/olefin isomerization processes are explored. / Thesis (PhD) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
7

Lligands hemilàbils en la reacció de Pauson-Khand intermolecular i asimètrica

Solà i Oller, Jordi 20 December 2006 (has links)
La reacció de Pauson-Khand (PK) és formalment una cicloaddició 2+1+1 entre un alquè, un alquí i una molècula de monòxid de carboni per donar lloc a una ciclopentenona. Aquesta reacció està mediada per una espècie de cobalt (0). El primer pas de la reacció és la formació d'un complex de dicobalthexacarbonil de l'alquí, d'estructura tetrahèdrica (per reacció entre l'alquí i Co2(CO)8). La posterior coordinació i inserció de l'olefina acabarà donant lloc a la ciclopentenona final. En aquesta reacció es poden formar fins a dos nous centres quirals de manera que és necessària la introducció d'un element quiral per controlar l'estereoquímica de la reacció. La coordinació amb un lligand quiral és l'aproximació més elegant per a desenvolupar versions asimètriques de la reacció. Dins del camp dels lligands destaquen els lligands bidentats P,S (PuPHOS i CamPHOS) desenvolupats al nostre grup de recerca. Aquets lligands es coordinen a un complex de cobalt en forma de pont, mitjançant el fòsfor i el sofre, donant lloc a dos diastereòmers. Cada un d'aquests diastereòmers reacciona amb elevada selectivitat amb olefines tensionades obtenint els corresponents adductes amb elevats excessos enantiomèrics.Els lligands bidentats PuPHOS i CamPHOS estudiats consten en la seva estructura d'un carboni unit a tres heteroàtoms (P, O, S) fet que confereix certa acidesa al protó que sustenta. Per tant, aquest protó pot establir una interacció estabilitzant per pont d'hidrogen 'no clàssic' amb un grup acceptor adequat, contingut en l'estructura de l'alquí. Degut a la quiralitat intrínseca dels lligands, aquesta interacció només és possible en un dels dos diastereòmers de manera que es produeix un reconeixement eficaç entre el lligand i el complex de cobalt. Com a acceptors de pont d'hidrogen s'han emprat amb èxit complexos d'amides i sulfones. D'aquesta manera s'obtenen elevats excessos diastereomèrics (de fins el 99%) en la reacció d'intercanvi de lligand. Els estudis realitzats per 1H-RMN, difracció de raig X i càlculs teòrics del complexos obtinguts confirma l'existència d'un enllaç d'hidrogen no clàssic entre el lligand i el grup acceptor de pont d'hidrogen (en els diastereòmers majoritaris). D'altra banda, els càlculs teòrics realitzats situen aquest enllaç dins el camp de les interaccions per pont d'hidrogen no clàssiques més fortes. La posterior reacció de Pauson-Khand dels complexos majoritaris obtinguts transcorre amb elevada selectivitat amb el norbornadiè. S'obtenen els adductes corresponents amb bons rendiments (fins el 99%) i excel·lents excessos enantiomèrics (fins el 99%).Per una altra banda s'ha sintetitzat una nova família de lligands: N-fosfinosulfinamides. Aquest tipus de compostos es troba descrit a la literatura. Aquests nous lligands, quirals en l'àtom de sofre, es coordinen també en forma de pont sobre els complexos de cobalt d'alquins mitjançant els àtoms de sofre i fòsfor. És el primer cop que es descriu la coordinació de compostos tipus sulfòxid a cobalt mitjançant l'àtom de sofre. La reacció de coordinació transcorre amb rendiments molt bons i selectivitats molt elevades, fins i tot en alquins no funcionalitzats (fins a 20:1 r.d.). La reacció de Pauson-Khand dels diastereòmers majoritaris, aïllables per cristal·lització en la majoria de casos, té lloc amb excel·lents rendiments i enantioselectivitats (fins a 99% de rendiment i 99% d'ee.). / "Hemilabile Ligands in the Pauson-Khand reaction".The Pauson-Khand reaction is a cycloaddition, promoted or catalysed by cobalt, between an alkene and an alkyne with insertion of a carbon monoxyde molecule to give a cyclopentenone. If the olefin is disubstituted, two new stereogenic centres can be created. Among the ligands designed for this reaction, we must highlight the CamPHOS and the PhuPHOS ligands. They are bidentate P, S ligands. When coordinated to a bimetallic cobalt complex, a bridged structure where the sulphur and the phosphorus are coordinated to different metal atoms is obtained.A unique methine moiety attached to three heteroatoms (O, P, S) and contained in the PuPHOS and CamPHOS ligands can serve as a strong hydrogen-bond donor. Nonclassical hydrogen bonding of this methine with an hydrogen-bond acceptor provides a completely diastereoselective ligand exchange process between an alkyne dicobalthexacarbonyl complex and a phosphine ligand. This weak contact has been studied by means of X-ray analysis, 1H NMR, and quantum mechanical calculations and revealed that thepresent interaction falls in the range of strong C-H···O bonds. The hydrogen-bond bias obtained in the ligand exchange process has been exploited in the asymmetric intermolecular Pauson-Khand reaction to yield the corresponding cyclization adducts in up to 99% ee.Finally, a new family of chiral ligands for the asymmetric PK reaction was synthesized . Starting from the known (R)-(+)- tert-butyl tert-butanethiosulfinate the corresponding tert-butylsulfinamides can be achieved. Deprotonation with BuLi at low temperature, alkylation with diphenylphosphine chloride yielded the desired ligands. In order to avoid the internal oxygen transfer a protection-deportection step as borane complexes must be included. After heating a dicobalt hexacarbonyl complex in toluene in presence of these new ligands two tetracarbonyl diastereomers are formed. The yields and diasereoselectivities obtained were excellent even when unfunctionalized alkynes were used. Thus mixtures of diastereomers in a 6:1 to 20:1 ratio are obtained in 50-80% yields. The Pauson-Khand reaction of the major diastereomers obtained with norbornadiene proceeded with excellent yields and enantiomeric excesses. Thus, in some cases quantitative yields and up to 99% ee are obtained in some cases.
8

Synthesis Of 2-heteroaryl Substituted Chiral Fused Cyclopenta[c]pyridine Derivatives Via Pauson-khand Reaction

Gumrukcu, Yasemin 01 October 2009 (has links) (PDF)
The racemic homoallylic and homopropargylic alcohol derivatives were resolved by applying chemoenzymatic method using various lipase type enzymes i.e., PS-C II, Lipozyme, CAL-B. The enantiomeric excess values of the resultant alcohols were determined by HPLC. These enantiomerically enriched homoallylic and homopropargylic alcohols were subjected to N-propargylation and N-allylation, respectively, by SN2 and modified Mitsunobu reactions. During the course of all reactions, stereochemistry of the chiral centers were under controlling according to the known reaction mechanisms. The resultant chiral N-tosylated enyne derivatives afforded the corresponding chiral fused cyclopenta[c]pyridinone derivatives (69, 73, 75 and 77) with acceptable chemical yields and excellent diastereoslectivity depending upon the conformational effect on the complete remote stereochemical control for the newly generated chiral centers. The chemoenzymatic applications done with biocatalysis (lipases) and the Pauson-Khand reaction are involved in &ldquo / Green Chemistry&rdquo / approach.
9

Remote Control Of The Diastereoselectivity In The Pauson

Sezer, Serdar 01 December 2011 (has links) (PDF)
In this thesis, an intramolecular Pauson-Khand reaction of chiral enynes derived from homoallyl, allyl and homopropargyl alcohols is described. For this purpose, 2-heteroaryl substituted homoallyl, allyl and homopropargyl alcohols are easily and efficiently resolved through enzymatic resolution in a high ee (91-99%) with a known stereochemistry. Each enantiomerically enriched enyne derived from homoallyl and homopropargyl alcohols affords the conformationally most stable diastereomeric cyclopenta[c]pyran ring system as a sole product, whereas enantiomerically enriched enynes derived from allyl alcohols give the diastereomeric cis:trans mixture of cyclopenta[c]furan ring system. In addition these, an intramolecular Pauson&ndash / Khand reaction of camphor tethered enynes derived from homoallyl, homomethallyl, and homopropargyl alcohols is also described. Accordingly, homoallyl, homomethallyl, and homopropargyl moieties are easily constructed on the camphor carbonyl group with excellent diastereoselectivity due to endo-face selectivity, and with known stereochemistry. Each enantiomerically pure enyne affords the conformationally most stable diastereomeric spirocyclic cyclopenta[c]pyran ring system.
10

Studien zur übergangsmetallvermittelten Synthese von bioaktiven carbocyclischen Nucleosiden und von Rotenoiden /

Lanver, Andreas. January 2006 (has links)
Universiẗat, Diss.--Köln, 2006. / Zsfassung in engl. Sprache.

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