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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.
91

Synthetic approaches to the angucycline antibiotics

Osman, Hasnah, n/a January 2005 (has links)
The stereoselective synthesis of urdamycinone B (17) was achieved in a 21% overall yield from C-glycosyl-naphthoquinone 197. The key reaction was the Diels-Alder cycloaddition reaction of 197 and siloxydiene (�)-117 promoted by a chiral Lewis acid derived from (S)-3,3�-diphenyl-1,1�-binaphthalene-2,2�-diol (291), BH₃.THF and acetic acid. An effective kinetic resolution of (�)-117 occurred. Four cycloadducts 199a-d were formed in a ratio between 84:8:2:6 and 70:9:2:19. Aromatisation of the mixture by treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gave 200a and 200b in 4:1 ratio. A sequence of reactions involving deacetylation, conversion of a phenyldimethylsilyl group into a hydroxyl group and photooxidation gave a 4:1 mixture of urdamycinone B (17) and its C-3 epimer (154). Separation of these products was achieved by high performance liquid chromatography (HPLC). The C-glycosyl donor, 1,3,4-tri-O-acetyl-2,6-dideoxy-D-glucopyranose (204), was synthesised from readily accessible tri-O-acetyl-D-glucal (237) using two approaches. The first involved a sequence of deacetylation, tosylation, lithium aluminium hydride (LiAlH₄) reduction and acetylation to give di-O-acetyl-6-deoxy-D-glucal (242). The triphenylphosphine hydrogen bromide (TPPHBr) catalysed addition of acetic acid to 242 gave 204 in overall yields ranging from 0 to 32%. The step involving the reduction of the tosylate intermediate was the cause of the variable yields. The alternative synthesis started with the TPPHBr catalysed addition of benzyl alcohol to 237. Subsequent deacetylation, tosylation and reduction with LiAlH₄ gave benzyl 2,6-dideoxy-D-glucopyranoside (250). Acetylation and hydrogenolytic debenzylation gave 3,4-di-O-acetyl-2,6-dideoxy-D-glucopyranose (247). Acetylation gave 204 in 40% overall yield. A third approach to 204 involved selective tosylation of methyl α-D-mannopyranoside (258) and subsequent treatment with 2,2-dimethoxypropane under acidic conditions to give acetonide 255. LiAlH₄ reduction of the tosylate gave methyl 6-deoxy-2,3-O-isopropylidene-α-D-mannopyranoside (256). Acidic hydrolysis of 256 and subsequent acetylation afforded 1,2,3,4-tetra-O-acetyl-6-deoxy-α-D-mannopyranoside (260). Treatment of 260 with hydrogen bromide in acetic acid and subsequent reductive elimination with a zinc-copper couple gave 242. The addition of acetic acid catalysed by TPPHBr afforded 204 in 18% overall yield. The final synthesis of 204 started with thiophenyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranoside (269). A sequence of deacetylation, tosylation and LiAlH₄ reduction gave thiophenyl 2,3-O-isopropylidene-6-deoxy-α-D-mannopyranoside (274). The structure of 274 was confirmed from a single crystal X-ray diffraction study. Hydrolysis of the isopropylidene group of 274 and subsequent acetylation afforded thiophenyl 6-deoxy-2,3,4-tri-O-acetyl-α-D-mannopyrannoside (282). Treatment of 282 with iodine monobromide and subsequent reductive elimination with zinc-copper couple gave 242. The TPPHBr catalysed addition of acetic acid to 242 afforded 204 in 19% overall yield. Differentially protected C-glycosyl donor, 1,3-di-O-acetyl-4-O-benzyl-2,6-dideoxy-D-mannopyranose (265), was synthesised from 274. The benzylation of 274 gave thiophenyl 6-deoxy-2,3-O-isopropylidene-4-O-benzyl-α-D-mannopyranoside (276). Acidic hydrolysis followed by acetylation afforded thiophenyl 6-deoxy-1,2-di-O-acetyl-4-O-benzyl-α-D-mannopyranoside (278) which, upon bromination by iodine monobromide, gave thiophenyl 6-deoxy-1,2-di-O-acetyl-4-O-benzyl-α-D-mannopyranosyl bromide (279). The reductive elimination of 279 with zinc-copper couple gave 3-O-acetyl-4-O-benzyl-6-deoxy-D-glycal (264). The TPPHBr catalysed addition of acetic acid to 264 afforded 1,3-di-O-acetyl-4-O-benzyl-2,6-dideoxy-D-mannopyranose (265) in 16% overall yield from 274. The instabillity of bromide 279 affected the yield of 265. A C-glycosylation study of 2-naphthol 227 and 1,4-dimethoxy-5-hydroxynaphthalene (205) with 2-deoxy-glycosyl acetates was undertaken. Boron trifluoride diethyl etherate (BF₃.Et₂O) and scandium triflate [Sc(OTf)₃] proved effective promoters. For example, the glycosylation reaction of donor 265 and 227, promoted by 0.5 equivalents of Sc(OTf)₃, afforded C-glycoside 2-hydroxy-1-[3�-O-acetyl-4�-O-benzyl-2,6-dideoxy-β-D-manno-hexopyranosyl]-naphthalene (289) in 85% yield.
92

Diels-alder reactions of a cyclopentadienone derivative

Gomes, Maria Goretti, January 2007 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on February 13, 2008) Vita. Includes bibliographical references.
93

Virantmycin und Spiculoinsäure A - die intramolekulare Diels-Alder-Reaktion in der Synthese komplexer Naturstoffe

Keck, Daniel January 2006 (has links)
Zugl.: Karlsruhe, Univ., Diss., 2006
94

Chiral Lewis acid catalyzed Diels-Alder reactions

Knol, Jochem, January 2008 (has links)
Proefschrift Rijksuniversiteit Groningen. / Auteursnaam op omslag: Joop Knol. Met lit. opg. - Met een samenvatting in het Nederlands.
95

Toward the synthesis of polycyclic aromatic compounds as nano-carbon cages

Zhang, Ruoxin, January 2008 (has links)
Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains vii, 45 p. : ill. Includes abstract. Includes bibliographical references (p. 24-26).
96

Étude de la réaction de Diels-Alder transannulaire de cyclotétradécatriénones de géométrie trans-trans-cis et trans-cis-cis comportant un diénophile activé approches en vue de la synthèse de diterpènes.

Barriault, Louis. January 1997 (has links)
Thèses (Ph.D.)--Université de Sherbrooke (Canada), 1997. / Titre de l'écran-titre (visionné le 24 août 2006). Publié aussi en version papier.
97

Étude de la réaction de Diels-Alder transannulaire de macrocycles à quatorze membres de géométrie trans-trans-trans comportant un diénophile activé ou non-activé

Bourque, Élyse. January 2001 (has links)
Thèses (Ph.D.)--Université de Sherbrooke (Canada), 2001. / Titre de l'écran-titre (visionné le 24 août 2006). Publié aussi en version papier.
98

Étude de la réaction de Diels-Alder transannulaire de macrocycle à 14 membres en vue de la synthèse de l'acide fusidique et des quassinoïdes

Fortin, Samuel. January 2003 (has links)
Thèses (Ph.D.)--Université de Sherbrooke (Canada), 2003. / Titre de l'écran-titre (visionné le 24 août 2006). Publié aussi en version papier.
99

Étude de la réaction de Diels-Alder transannulaire sur des macrocycles à quatorze membres de géométrie trans-trans-trans en vue de la synthèse des diterpènes cassaïne et néotripterifordine

Phoenix, Serge. January 2004 (has links)
Thèses (Ph.D.)--Université de Sherbrooke (Canada), 2004. / Titre de l'écran-titre (visionné le 24 août 2006). Publié aussi en version papier.
100

Approches en vue de la synthèse d'anthracyclines par la stratégie des Diels-Alder a dienes transmissibles

Beauchemin, Sophie. January 1999 (has links)
Thèses (M.Sc.)--Université de Sherbrooke (Canada), 1999. / Titre de l'écran-titre (visionné le 19 juillet 2006). Publié aussi en version papier.

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