http://hdl.handle.net/10464/2245 Tue, 21 May 2013 20:55:02 GMT 2013-05-21T20:55:02Z http://hdl.handle.net/10464/3417 Development of thermally stable versions of the Burgess Reagent : approaches to the chemoenzymatic total synthesis of morphine Metcalf, Thomas A. The present studies describe our recent work on expanding the use of the Burgess reagent and its reaction with oxiranes. Several new variants of the Burgess reagent and its chiral auxiliary version were evaluated for their thermal stability by NMR spectroscopy. Three new versions of the reagent were synthesized and their stability was determined. The reactivity of all five Burgess reagents was compared in a dehydration reaction and reactions with epoxides and diols. Progress toward a chemoenzymatic synthesis of morphine is also included in this report. The synthesis began with the whole cell oxidation of bromobenzene by Escherichia coli JMI09(pDTG601). The preparation of several precursors for a key step involving the lohnson-Claisen rearrangement and progress toward the total synthesis are described. Fri, 14 Oct 2011 00:00:00 GMT http://hdl.handle.net/10464/3417 2011-10-14T00:00:00Z http://hdl.handle.net/10464/3189 Asymmetric hydrogenation of alkenes with cationic iridium(I) complexes of 2-phosphino-1-aminoferrocene ligands Van Belle, Lori Iridium complexes with bidentate P,N ligands represent a class of catalysts that significantly expand the application range of asymmetric hydrogenation. New substrate classes, for which there have previously been no suitable catalysts, can now be efficiently hydrogenated in high conversion and enantioselectivity. These substrates are often of synthetic importance, thus iridium catalysis represents a significant advance in the field of asymmetric catalysis. Planar chiral ferrocenyl aminophosphine ligands in which both heteroatoms were directly bound to the cyclopentadienyl ring were prepared by BF3-activated lithiationsubstitution in the presence of a chiral diamine in 49-59% yield and 75-85% enantiomeric excess. Some of these ligands were recrystallized to enantiomeric purity via ammonium fluoroborate salt formation of the phosphine sulfide. A crystal structure of one of these compounds was obtained and features an intramolecular hydrogen bond between the nitrogen, hydrogen, and sulfur atoms. Neutralization, followed by desulfurization, provided the free ligands in enantiomeric purity. Iridium complexes with these ligands were formed via reaction with [Ir(COD)Clh followed by anion exchange with NaBArF. These complexes were successfully applied in homogeneous hydrogenation of several prochiral substrates, providing products in up to 92% enantiomeric excess. Variation of the dimethyl amino group to a pyrrolidine group had a negative effect on the selectivity of hydrogenation. Variation of the substituents on phosphorus to bulkier ortho-tolyl groups had a positive effect, while variation to the more electron rich dicyclohexyl phosphine had a negative effect on selectivity. Tue, 08 Mar 2011 00:00:00 GMT http://hdl.handle.net/10464/3189 2011-03-08T00:00:00Z http://hdl.handle.net/10464/3033 Enantiodivergent chemoenzymatic synthesis of Balanol and approaches to the synthesis of (+)-Codine Gilmet, Jacqueline The present thesis reviews the development of a formal enantiodivergent synthesis of the (+)- and (-)-isomers of balanol. This approach commences from a cis-dihydrodiol derived from the enzymatic dihydroxylation of bromobenzene. The stereochemistry of the diol is used to direct the synthesis of two different aziridines, each used in the formal synthesis of one enantiomer of balanol. Also described are several enantioselective approaches to (+ )-codeine. Each strategy begins with the enzymatic dihydroxylation of p-bromoethylbenzene and involves a Mitsunobu inversion and intramolecular Heck reaction as key steps. Mon, 25 Oct 2010 00:00:00 GMT http://hdl.handle.net/10464/3033 2010-10-25T00:00:00Z http://hdl.handle.net/10464/2910 Iridium(I) complexes of phenanthroline-derived benzimidazolylidenes : synthetic, structural and catalytic studies Du, Xiangdong. N-heterocyclic carbenes (NHCs) have undergone rapid development in recent years. Due to their strong a-electron donation and structural variability properties, NHCs are becoming a major class of ligands in organometallic chemistry. Compared with the other two types of NHCs (imidazolylidenes and imidazolinylidenes), benzimidazolylidenes have not been well represented. Limited synthetic approaches may impede the development ofbenzimidazolylidenes. This thesis is focused on the synthesis of phenanthroline-derived benzimidazolylidene ligands and their metal complexes. A series of benzimidazolylidene-iridium complexes were synthesized and characterized spectroscopically and crystallographic ally. All of the new complexes showed varying degrees of catalytic activity and enantioselectivity toward transfer hydrogenation and asymmetric hydrogenation. The best results were achieved in hydrogenation of methyl-2-acetamidoacrylate, which afforded (-)-(R)-methyl-2-acetamidopropanoate in 97% yield and 81 % ee. Mon, 16 Feb 2009 15:45:57 GMT http://hdl.handle.net/10464/2910 2009-02-16T15:45:57Z