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dc.contributor.advisorBurgess, Kevin
dc.creatorZhu, Ye
dc.date.accessioned2012-07-16T15:56:49Z
dc.date.accessioned2012-07-16T20:33:03Z
dc.date.available2012-07-16T15:56:49Z
dc.date.available2012-07-16T20:33:03Z
dc.date.created2011-05
dc.date.issued2012-07-16
dc.date.submittedMay 2011
dc.identifier.urihttp://hdl.handle.net/1969.1/ETD-TAMU-2011-05-9231
dc.description.abstractHydrogenation of "largely unfunctionalized" alkenes has been an active area of research for about a decade. Many catalysts have been prepared but we noticed that comparatively few substrates have been studied and none of these hydrogenations provided useful chirons for the organic synthesis area. That motivated us to investigate asymmetric hydrogenations of chiral acyclic alkenes, which are seldom used for hydrogenations and usually the reactions are fully substrate controlled. It emerged that such reactions could provide a concise entry points into chirons that can be used to prepare many natural products. Asymmetric hydrogenations of functionalized, but not coordinatively functionalized, alkenes have been used to prepare several chirons for syntheses ofpolyketide natural products using our N,carbene Crabtree's catalyst analog. Starting from optically active starting materials (eg Roche esters, lactic acid, glyceraldehyde dimethyl ketals, amino acids), highly optically active chiral alkenes can be made in several steps with high yield. With the iridium catalyzed asymmetric hydrogenations, chiral ethers, 1,3-hydroxymethyl chiron, alpha-methyl-beta-hydroxy-gamma-methyl chiron, alpha-methyl-gamma-alkyl-gamma-amino acid can be obtained with high stereoselectivities. With those well developed methodologies, (-)-dihydromyoporone, (-)-spongidepsin, (-)-invictolide have been prepared with high efficiency. Not like the vinyl acetate, which can be hydrogenated quite well with many Rh catalysts, the alkyl vinyl ether does not have a coordination functional group nearby, hence it is a difficult substrate for asymmetric hydrogenation and there are relatively few iv reports. Also the simple alkyl enol ether is quite acid sensitive and the Pfatlz's type N,PIr catalysts cannot hydrogenate the simple alkyl enol ethers well under the standard hydrogenation conditions. We explored many alkyl enol ethers and found some of them can be hydrogenated efficiently (50 bar H2, 1 mol percent N,carbene-Ir catalyst, 25 degree C) with high enantioselectivities (up to 98 percent ee). This study led us to suspect that more protons were produced when N,P-Ir catalyst precursors were used relative to the corresponding carbene catalyst since the former only gave complex mixture when being used. DF calculations and several other experiments supported this postulation.en
dc.format.mimetypeapplication/pdf
dc.language.isoen_US
dc.subjectN,carbene-Iridiumen
dc.subjectdiastereoselectiveen
dc.subjecthydrogenationen
dc.subjectalkeneen
dc.subjectchironen
dc.titleAsymmetric Hydrogenations of Chiral Acyclic Alkenes for Important Chiron Synthesesen
dc.typeThesisen
thesis.degree.departmentChemistryen
thesis.degree.disciplineChemistryen
thesis.degree.grantorTexas A&M Universityen
thesis.degree.nameDoctor of Philosophyen
thesis.degree.levelDoctoralen
dc.contributor.committeeMemberGladysz, John
dc.contributor.committeeMemberConnell, Brian
dc.contributor.committeeMemberAnthony, Rayford
dc.type.genrethesisen
dc.type.materialtexten


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