Transition metal catalyzed reactions have an important place in synthetic chemistry, but the mechanistic details for many of these reactions remain undetermined. Through a combination of experimentally determined 13C kinetic isotope effects (KIEs) and density functional theory (DFT) calculations, some of these reactions have been investigated. The cyclopropanation of an olefin catalyzed by rhodium (II) tetrabridged complexes has been shown to proceed through an asynchronous, but concerted mechanism. DFT does not provide an accurate transition structure for the reaction of an unstabilized carbenoid with an olefin, but it does predict an early, enthalpically barrierless transition state which is consistent with the reactivity of unstabilized carbenoids. For the case of stabilized carbenoids, the theoretical structures predict the KIEs accurately and a new model is proposed to explain the selectivity observed in Rh2(S-DOSP)4-catalyzed cyclopropanations. The chain-elongation step of atom transfer radical polymerization (ATRP) has been shown to be indistinguishable from that of free radical polymerization (FRP) for the CuBr/2,2??-bipyridine system. While DFT calculations predict an earlier transition state than observed, the calculations suggest that with increasing levels of theory the predicted KIEs come closer to the observed KIEs. A recently proposed [2 + 2] mechanism for the cyclopropenation of alkynes catalyzed by Rh2(OAc)(DPTI)3 has been shown not to be a viable pathway. Rather, the experimental KIEs are predicted well by canonical variational transition state theory employing the conventional mechanism for cyclopropenation via a tetrabridged rhodium carbenoid. DFT calculations also suggest an alternative explanation for the observed enantioselectivity. The 13C KIEs for metal-catalyzed aziridination have been measured for three separate catalytic systems. While the KIEs do not completely define the mechanism, all of the reactions exhibit similar KIEs, implying similar mechanisms. A surprising feature of this system is the presumed nitrene intermediate??s triplet spin state. This complicates the DFT analysis of this system.

Dans ce mémoire, deux principaux sujets seront présentés. Nos efforts se sont d’abord tournés vers la synthèse du cylindrocyclophane F, un [7,7]-paracyclophane naturel, puis vers l’élaboration d’une nouvelle classe d’hétérocycles fluorescents. Premièrement, la cyclopropanation, une des étapes clés de la synthèse du cylindrocyclophane F, ainsi qu’une nouvelle voie de synthèse passant par une réaction de cyclopropénation ont été revisitées. La possibilité d’employer une méthode de macrocyclisation, incluant une réaction de couplage de Suzuki sur deux centres sp3, a ensuite été étudiée sur un substrat modèle. Deuxièmement, la synthèse de benzo[a]imidazo[2,1,5-c,d]indolizines à partir de N-[(6-bromo-2-pyridinyl)méthyl]benzamides a été développée. Dans un premier temps, le tandem cyclodéshydratation/aromatisation effectué en présence de 2-méthoxypyridine a été optimisé afin d’obtenir la 5-bromo-3-phénylimidazo[1,5-a]pyridine. Puis, une arylation intramoléculaire en présence d’une quantité catalytique d’un complexe de palladium a permis d’obtenir l’hétérocycle fusionné désiré. Les propriétés photochimiques de cette nouvelle classe d’hétérocycles seront aussi présentées. / In this thesis, two main points will be introduced. First, we focused our efforts on a synthetic approach towards cylindrocyclophane F, a natural [7,7]-paracyclophane. Then, the synthesis of a new fluorescent class of molecule will be disclosed. First, an asymmetric cyclopropanation, one of the key steps of the synthesis of cylindrocyclophane F, will be revisited. Furthermore, a new route, including a cyclopropenation reaction, was explored. Then, the possibility of using a Suzuki coupling reaction on two sp3 centres for macrocyclisation has been studied on a model substrate. In a separate study, the synthesis of benzo[a]imidazo[2,1,5-c,d]indolizines from N-[(6-bromo-2-pyridinyl)methyl]benzamides will be disclosed. A mild cyclodehydratation-aromatisation was performed in the presence of 2-methoxypyridne in order to obtain 5-bromo-3-phenylimidazo[1,5-a]pyridine. This sequence was followed by an intramolecular direct arylation to form the desired compound. The photophysical properties of this new heterocycle class were measured.

Microwave-Assisted Thermolysis of ortho-Substituted Aroylsilanes Marc Tremblay Master of Science Department of Chemistry University of Toronto 2008 The microwave-assisted thermolysis of ortho-substituted aroylsilanes has been investigated. When irradiated at 250ºC in DMSO or o‑dichlorobenzene for 10 minutes, aroylsilanes form siloxycarbenes that react following different pathways depending on the solvent and the structure of the starting material. It is shown that in the case of substrates having an O‑allyl or an O‑propargyl chain ortho to the acylsilane, cycloaddition occurs followed by a cascade ring opening to give respectively chroman‑4-one and chromen‑4-one derivatives in up to 66% yield. Among the major competitive pathways were the insertion of the siloxycarbene into allylic C–H bonds and decomposition of the acylsilane group to the corresponding aldehyde, followed by Claisen rearrangement.

Microwave-Assisted Thermolysis of ortho-Substituted Aroylsilanes Marc Tremblay Master of Science Department of Chemistry University of Toronto 2008 The microwave-assisted thermolysis of ortho-substituted aroylsilanes has been investigated. When irradiated at 250ºC in DMSO or o‑dichlorobenzene for 10 minutes, aroylsilanes form siloxycarbenes that react following different pathways depending on the solvent and the structure of the starting material. It is shown that in the case of substrates having an O‑allyl or an O‑propargyl chain ortho to the acylsilane, cycloaddition occurs followed by a cascade ring opening to give respectively chroman‑4-one and chromen‑4-one derivatives in up to 66% yield. Among the major competitive pathways were the insertion of the siloxycarbene into allylic C–H bonds and decomposition of the acylsilane group to the corresponding aldehyde, followed by Claisen rearrangement.