| Chapter 1. Intramolecular coupling of CO and alkenes with benzimidazole cores was described in this chapter. Though the cyclizations were successful, the yields were modest for the desired ketone products. Isomerization of the double bond, which led to decomposition of the starting material, was found to be a significant problem. The decomposition of the starting material could be attenuated, but not completely prohibited, by increasing the CO pressure during the reaction. During the course of investigating this process, an intramolecular Rh(I) catalyzed hydroarylation reaction of benzimidazole was discovered, the details of which are discussed in subsequent chapters.; Chapter 2. An intramolecular C-H/alkene coupling was discovered that provides access to a variety of multicyclic heterocyclic products. Compounds with both five- and six-membered rings were prepared, and 1,1-disubstituted, 1,2-disubstituted, and trisubstituted double bonds participate in the cyclization. An N-heterocyclic carbene (NHC) complex was found to be the active catalyst in the Rh(I) catalyzed intramolecular coupling of an alkene to a C-H bond of benzimidazole. The kinetics of the cyclization were studied by 1H NMR spectroscopy. The catalytic cyclization was found to be zero order in substrate and first order in catalyst concentration with a rate constant of 4.2 +/- 0.6 x 10-4 sec -1 at 135°C, consistent with the N-heterocyclic carbene complex being the resting state of the catalyst. Furthermore, DFT calculations with a model system were performed. The calculations supported the hypothesis of a mechanism that proceeds via the NHC intermediate and suggested that the rate-limiting step involved carbene insertion into the Rh-alkene bond.; Chapter 3. The intermolecular coupling of unactivated alkenes to a range of heterocycles using a Rh(I) catalyst was investigated. A variety of functional groups were incorporated into the alkene, including esters, nitriles, and acetals. Furthermore, the reaction tolerated heterocycles substituted with both electron-rich and electron-deficient groups. (Abstract shortened by UMI.)... |
