Natural products serve as a major resource for many pharmacologically-active drugs found in the market today. Using natural products as medicines, however, is associated with many limitations such as availability and isolation. An alternative to this is the synthesis of these compounds, which can be done using two different approaches: (1) Total synthesis of the molecule, and (2) A semi-synthetic approach. Total synthesis generally involves synthesis of the target molecule by assembling the ring systems or the core skeletal framework of the natural product. There are numerous methods reported in the literature for the synthesis of these ring systems. Despite this, there is always a quest for new methods; methods with improved efficiency in terms of chemo-, regio- and stereoselectivities. As a result, new synthetic tools are needed to address these issues. These new tools can be the development of new catalysts, new techniques, or innovative methodologies, which will allow new transformations and aid in the synthesis of complex natural products. In recent years small, strained molecules such as cyclopropanes, cyclobutanes and cyclopropenes, have been successfully employed for the synthesis of complex ring systems. In this dissertation a new method to access certain carbocyclic and heterocyclic ring systems using cyclopropanes as building blocks will be presented. This involves synthesis of novel cyclopropanes by intermolecular reaction between substituted styrenes and different alpha-arylmethyl-alpha-diazo compounds in the presence of Rhodium catalysts. The challenge in the synthesis of these cyclopropanes is that these diazo compounds are notorious for undergoing beta-hydride elimination reactions, thus limiting their use for intermolecular reactions. In this study, we aim to synthesize the proposed cyclopropanes in good yields while minimizing, if not completely eliminating, the beta-hydride elimination reaction. The first half of the thesis discusses the different approaches taken to synthesize the desired cyclopropanes with limited success. However using Rh2 (S-PTTL)3 TPA as the catalyst and optimizing the reaction conditions allowed us to synthesize these cyclopropanes in moderate to good yields. The second part of the thesis focuses on the study of ring opening reactions of the cyclopropanes synthesized using various Lewis acids.

No description available.

A series of penta-aryl/alkyl-1-(toluene-4-sulfonyl)-4,5-dihydro-1H-pyrazole 5a-c was synthesized by addition of methyllithium or phenylllithium followed by trapping the nitrogen anion intermediate with tosyl-fluoride to cyclic azines 2a,b. Addition of methyllithium or phenyllithium to 5a-c generated a series of hexa-aryl/alkylsubstituted-4,5-dihydro-3H-pyrazoles 6a-c. Neat thermolysis of hexa-aryl/alkylsubstituted-4,5-dihydro-3H-pyrazoles 6a-c at 200◦C produced hexa-aryl/alkylsubstituted cyclopropanes 7a-c in high yield.

No description available.

Thesis (Ph. D.)--University of Wisconsin, 1941. / Typescript (carbon copy). Includes bibliographical references.

No description available.

Thesis (M.Sc. (Organic Chemistry))--Mahidol University, 1982.

The objective of this research is to synthesize, fully characterize, and investigate the catalytic properties of a series of rhodium(II) acetate derivatives. On its own, rhodium(II) acetate possesses the ability to catalyze the formation of cyclopropanes—strained, three-carbon rings that are a defining structural feature of the group of insecticides known as permethrins (found naturally in chrysanthemum flowers). Alone, though, the rhodium(II) acetate ‘paddlewheel’ structure does not selectively catalyze the formation of the biologically active version of the cyclopropane product; a mix of products is created that must then be separated. The separation process is expensive in time and % yield. With every step in the purification of the permethrin mixture, a significant amount of product is sacrificed. Thus, the permethrins in their commercial pure form are prohibitively expensive for most desired applications. Extracted permethrins are only used in the treatment of head lice and as flea/tick treatment of pets. With the goal of enhancing the catalytic complex’s selectivity for the biologically active cyclopropane confirmation (atomic arrangement), a p-tolunitrile ligand (molecular ‘adduct’) has been attached to rhodium(II) acetate. The complexes thus synthesized have been characterized by Single Crystal X-ray Crystallography, IR, NMR and UV-visible spectroscopies and elemental analysis. The catalytic properties of such nitrile adducts of rhodium(II) acetate are currently under investigation.

Isolated from Spongosorites sp., Dragmacidin E is of synthetic interest due to its biological properties and novel molecular structure. A promising therapeutic target, its synthetic challenge is attributed to its heptacyclic core. In this study, we propose the synthesis of a Dragmacidin E heptacyclic core precursor, mediated through a Lewis acid (LA) mediated cyclization of an acceptoreptor-donor (AAD) cyclopropane. Utilizing a model study, alkoxy AAD cyclopropanes were investigated to develop a protocol for precursor synthesis. After generating various ethyl-α-diazobenzoyl acetate derivatives, the metal catalyzed cyclopropanation reaction of these compounds was studied. With vinyl acetate and Rh2esp2, acetoxy AAD cyclopropanes were synthesized in yields ranging from 12 % - 53 %. These cyclopropanes were successfully generated and rearrangement into dihydrofuran products was avoided. To complete our model study, LA cyclization of acetoxy AAD cyclopropanes was studied. Using stoichiometric quantities of TiCl4<.sub>, naphthol derivatives were synthesized in one step.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.