published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

The osmium-mediated aminohydroxylation reaction is a powerful oxidation that introduces a hydroxyl group and a protected amino group in a syn relationship across an olefinic double bond. This study concerns one approach to controlling the regioselectivity of this oxidation. Introduction I The mechanism, scope and limitations of the aminohydroxylation reaction are discussed, with particular attention to the asymmetric version, providing a background from which the newly developed methodology has emerged. Results and Discussion I Development of the reaction This section concerns the original attempts to perform the tethered aminohydroxylation reaction, and early process optimisation to maximise the yield of aminohydroxylated product produced. Scope of the reaction This section details the results of the TA reaction as applied to further allylic carbamates demonstrating the applicability of the reaction to other olefinic geometries. The diastereoselectivity of the reaction in cyclic and acyclic systems is reported, and a model to explain the observed results discussed. Also covered within are the syntheses of the various substrates and proof of the stereochemistry of the products. Mechanistic investigations Work involving attempts to isolate a catalytic intermediate from the reaction is described. A crystal structure of this intermediate is discussed. Introduction II The isolation and physiological properties of the antibiotic compound hygromycin A are described. Prior synthetic routes towards this compound are discussed. Results and Discussion II Three approaches towards the aminocyclitol unit of hygromycin A, employing the tethered aminohydroxylation reaction, are outlined. Two of these allow for potential future development and completion of the synthesis.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

The oxidation of olefins by transition metal complexes leading to epoxide or ketonic products has been reviewed, with an emphasis on non-free radical processes. The formation of cycloadducts by reaction of <u>bis</u> (triphenylphosphine )- platinum(O)dioxygen with the α,β-unsaturated carbonyl compounds <u>trans</u> but-2-enal, propenal, cyclohex-2-en-1-one, <u>exo</u> 2-methvlenecyclohexan-1-one and 3-phenylprop- 2-enal was investigated by H- and ³¹P- nuclear magnetic resonance (n.m.r.). The cycloadducts derived from <u>trans</u> but-2-enal and propenal were thermally unstable in solution and further reacted to form stable, isolable complexes. The mechanism by which the cycloadduct <u>cis</u> [4-<u>trans</u>(prop-2-enyl )-1,1-bis( triphenyl - phosphine)platina-2,3» 5-trioxacyclopentane] , I , was transformed into <u>cis</u> [<u>trans</u>- (5-formyl-4-methyl)-1,1-bis(triphenylphosphine )platina-2 t 3-dioxacyclopentane] , II , was investigated by H- and H-n.m.r. utilising <u>trans</u> 4-[²H₃]but-2-enal. A mechanism which involved both exchange of free <u>trans</u> but-2-enal with I and reaction to give II was proposed; a computer model, based upon numerical integration of the alternative rate equations was in good agreement with this proposition. The chemical reactivity of II with a variety of reagents was explored. In particular, the reaction of II with trifluoroacetic acid gave <u>trans</u> 2-formyl- 3-methyloxirane in high yield and stereoselectivity. The dynamic behaviour of <u>cis</u>[<i>bis</u>(triphenylphosphine)(2₃,3'-m)(<u>trans</u> - but-2-enal )platinum(0)] was observed by variable temperature P-n.m.r. and explained by the interconversion of carbonyl rotamers. The preparation of iridium(I) olefin and peroxo complexes has been described Chloro<u>bis</u> triphenylphosphine) (1,2-m) (ethene )dioxygen iridium( I) , III , and related complexes were found to oxidise terminal olefins to their methyl ketones stoichiometrically, by a non-free radical process. The mechanism has been discussed.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy