The iridoids are a large family of monoterpenoid natural products that possess a wide range of biological activities. A great deal of research has already been done in the field of iridoid total synthesis, but limitations still remain. Specifically, few syntheses of iridoid β-glycosides have been reported. This work describes the 14 step asymmetric total synthesis of the iridoid β-glycoside (+)-geniposide utilizing a phosphine-catalyzed [3+2] cycloaddition as the key step. Other noteworthy steps in the synthesis include a palladium-catalyzed kinetic resolution and a previously unutilized method for iridoid glycosidation. In addition to describing the synthesis of (+)-geniposide, this dissertation will also review 1) phosphine-catalyzed cycloaddition reactions and 2) previous enantioselective total syntheses of iridoid glycosides. / text

This thesis details the synthesis of novel Rh(I) and Rh(III) bis-phosphine fragments, and their use, along with other known rhodium species, to investigate the reactivity of amine-boranes, with a particular focus on the dehydrocoupling of the secondary amine-borane H3B.NMe2H (DMAB). Chapter 2 utilises the new mixed phosphine, PtBuiBu2, to investigate the role of the phosphine with regard to the corresponding low-coordinate organometallic species isolated. Their coordination and reactivity with amine-boranes is studied, leading to the development of a mechanism for an alkene hydroboration catalyst that employs H3B.NMe3 (TMAB). The final section of the chapter studies several fluxional processes pertinent to rhodium and iridium complexes of the model amine-borane TMAB using H/D exchange and low temperature NMR experiments. In Chapter 3, the mechanism of dehydrocoupling of DMAB is investigated in detail, employing catalysts based on the cationic bis¬-phosphine Rh fragment, {Rh(PCy3)2Ln}+. A series of stoichiometric and catalytic reactions are probed using NMR spectroscopy and mass spectrometry, revealing a complex mechanistic landscape. Subtleties include: the product of dehydrocoupling, [H2BNMe2]2, acting in an autocatalytic role; and parallel dehydrogenation of DMAB by a neutral catalyst present in a low but constant concentration. The mechanism was additionally interrogated through kinetic simulations conducted by Prof. Guy C. Lloyd-Jones (University of Bristol). From this, a generic mechanistic scheme has been suggested, aspects of which can be applied to transition metal and main group systems reported to catalyse the dehydrocoupling of DMAB. The final chapter moves on from cationic rhodium fragments to investigate the reactivity of the neutral rhodium species, Rh(H)2(PCy3)2Cl and [Rh(PCy3)2Cl]2, with amine-boranes. The mechanism by which Rh(H)2(PCy3)2Cl catalyses the dehydrogenation of DMAB has been investigated through initial rate and H/D exchange experiments, leading to the proposal of a reaction scheme. Additionally, the formation and characterisation of a base-stabilised boryl species has been reported resulting from the reactivity of an amino-borane with [Rh(PCy3)2Cl]2.

The mechanism of a conjugate addition of an alcohol to an alkynic acid ester using a phosphine catalyst was investigated using pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS) and proton and phosphorus nuclear magnetic resonance (NMR) experiments. Since ESI-MS only detects charged species, and only the phosphonium intermediates and by-products were visible by ESI-MS, 1H NMR was used to track the disappearance of the starting alkyne and the appearance of the conjugate addition product over time. 31P NMR was used to quantify the ESI-MS results. By-product formation was shown to out-compete product formation upon fast addition of alkyne, but with dropwise addition of alkyne, product was shown to dominate. A detailed numerical model was developed using PowerSim software to test mechanistic hypotheses. The experimental results were shown to be consistent with the mechanism proposed by Inanaga, and the cycle was elaborated to account for by-product formation. Piers’catalyst, a ruthenium complex with a phosphonium-functionalized carbene ligand, is a fast-initiating living catalyst for a number of olefin metathesis reactions, including ring-opening metathesis polymerization (ROMP) and cross metathesis (CM). Catalyst speciation was monitored in real-time for the ROMP of norbornene and the CM of 1-hexene using PSI-ESI-MS. The expected mass distribution of charged polymer-catalyst species were not observed, but merely catalyst and decomposition species were visible by ESI-MS. NMR and gel permeation chromatography (GPC) were used to determine quantitatively the presence of polymer and the polydispersity index, respectively. The results suggest that while Piers’ catalyst is indeed fast-initiating, the propagation rate greatly outstrips the initiation rate. In a foray into the area of chemical education, a well-known pH-induced colour change exhibited by the anthocyanins in red cabbage was developed into a simple – and ingestible – classroom demonstration. / Graduate / 0485

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 240-150). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 240-150). Also available on the Internet.