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The first comprehensive account of Diels-Alder reactions occurring by a simultaneous self-assembly of the components and catalysis of the reaction via a Lewis Acid (LA) is presented in this study. The synthetic usefulness of the intramolecularity achieved by temporary connection of DA reaction components has been combined with the benefits of LA catalysis to overcome the regio- and stereochemical diversities associated with DA reactions of unsymmetrically substituted dienes and dienophiles. LA's employed in this study act both as temporary connectors (by binding to LB sites of the diene and dienophile) and as catalysts (by complexation to oxygen of carbonyl moieties of the dienophiles). Formation of the tether, cycloaddition; and removal of the transient linker all occurs in a single operation.* To illustrate the high selectivity accomplished in this approach, an experimental model system consisting of unsymmetrically substituted dienol 6 and methoxy diene 397 and an unsymmetrically substituted dienophile (methyl acrylate, MAC) was designed. Thermal combination of either of these two dienes with MAC produces nearly equimolar mixtures of all four possible adducts illustrating the unselective nature of the reactions. Use of LA's to mediate the reaction between dienol 6 and MAC results in exclusive regio- and stereoselective formation of a single adduct. In contrast, application of the same LA's for the reaction between the methoxy diene and MAC either results in the formation of two 'endo' regioisomers in low yield or no reaction at all.* Exclusive formation of a single adduct for the reactions of 6 is attributed to a process in which the LA both pre-organizes the reactants and catalyzes the cycloaddition. This phenomenon is not expected to be observed in the reactions of the methoxy diene. The difference in the behavior of the two dienes is ascribed to the difference in their interactions with the LA's. Dienol 6 is able to bind covalently and irreversibly to the LA's while methoxy diene 397 is only able to co-ordinate to the LA's in a reversible manner. Mechanistic studies strongly support the self-assembled pathway and exclude other potential routes. Reactions of dienol 6 with other structurally suitable dienophiles under similar LA mediated conditions exhibit higher selectivities and reactivities in comparison with their uncatalyzed counterparts. Use of a structurally similar chiral dienol induces a highly diastereoselective cycloadditions with different dienophiles, whereas the thermal versions of the reactions again produce all possible adducts. The strategy has also been used for DA reactions of ' 2H'-thiopyran dienols with dienophiles 'N'-acroyl-2-oxazolidinone (NAO), ('E')-3-[3-(methoxycarbonyl)propenoyl]-1,3-oxazolidin-2 -one (MCPO), and 'N'-phenylmaleimide (NPM). Use of MgII is demonstrated to be effective to stereoselectively catalyze reactions which are unselective thermally or do not proceed at all. *Please refer to dissertation for diagrams.

The Bucherer-Bergs reaction is a classical multi-component reaction that yields hydantoins, which can be hydrolysed to afford α-amino acids. Hydantoins have many uses in modern organic synthesis, and this moiety has been included in a number of therapeutic agents, which have a wide range of biological activities. Herein, we report a mild synthesis of 5- and 5,5-substituted hydantoins from α-aminonitriles using Hünig’s base and carbon dioxide. This reaction can be performed in excellent yields, using a variety of organic solvents and is applicable to a range of substrates. In an extension to the above methodology, a one-pot Lewis acid-catalysed synthesis of hydantoins from ketones has also been developed and optimised in organic media. This reaction can be performed in excellent yields and is suitable for the synthesis of 5- and 5,5-substituted hydantoins.

Kationische Zinkkomplexe werden als katalytisch aktive Spezies zahlreicher Lewis-Säure-katalysierter Reaktionen vermutet. Die diesen Katalysereaktionen zugrunde liegenden Mechanismen sind jedoch unzureichend verstanden. Das Ziel der vorliegenden Dissertation ist die Synthese strukturell definierter kationischer Zinkorganyle als Modellverbindungen für katalytisch aktive Spezies zinkkatalysierter Reaktionen. Der Fokus liegt auf Zinkverbindungen mit Cyclopentadienylliganden (Cp-Liganden), da Cp-Liganden ungewöhnliche Bindungssituationen stabilisieren können. In dieser Arbeit wird die erfolgreiche Synthese und Charakterisierung mehrerer kationischer Zinkkomplexe des Pentamethylcyclopentadienylliganden (Cp*-Liganden) beschrieben. Ein gemeinsames Strukturmerkmal dieser Komplexe besteht in der Koordination des Zinkatoms durch einen Cp*-Liganden sowie durch Neutralliganden. Die hohe Elektrophilie dieser Verbindungen ließ sich durch Reaktivitätsuntersuchungen belegen. Ein weiterer Ansatz zur Stabilisierung kationischer Zinkverbindungen besteht in der Verwendung funktionalisierter Cp-Liganden, die über eine neutrale Donorgruppe in einer Seitenkette verfügen. Es wurden neutrale und kationische Zinkkomplexe amino- sowie thiofunktionalisierter Cp-Liganden synthetisiert und charakterisiert. Für die kationischen Komplexe konnte eine intramolekulare Stabilisierung des Zinkatoms durch die Donorgruppe nachgewiesen werden. Einige der in dieser Arbeit beschriebenen Zinkkomplexe wurden als Präkatalysatoren intermolekularer Hydroaminierungsreaktionen eingesetzt, wobei teilweise hohe katalytische Aktivitäten erreicht wurden. Untersuchungen zum Mechanismus der Katalysereaktionen zeigten, dass eine hohe Elektrophilie des Zinkzentralatoms für eine effektive Katalyse entscheidend ist. / Cationic zinc complexes are assumed to act as catalytically active species in various Lewis acid catalyzed reactions. However, the mechanisms of these reactions are poorly understood. The aim of this dissertation is to synthesize structurally well-defined cationic zinc organyls as model compounds for catalytically active species in zinc catalyzed reactions. The thesis focuses on zinc complexes bearing cyclopentadienyl (Cp) ligands, as Cp ligands can stabilize unusual bonding situations. The successful synthesis and characterization of several cationic zinc complexes with pentamethylcyclopentadienyl (Cp*) ligands is described. As a common structural feature of these complexes, the zinc center is coordinated by a Cp* ligand and additional neutral ligands. The highly electrophilic character of these compounds was proven in reactivity studies. A further approach to stabilize cationic zinc compounds is to apply functionalized Cp ligands featuring a donor group in a side chain. Neutral and cationic zinc complexes bearing amino- and thio-functionalized Cp ligands were synthesized and characterized. The cationic donor-functionalized complexes were shown to exhibit an intramolecular stabilization of the zinc atoms by the donor groups. Several zinc complexes which are described in this thesis were examined as precatalysts in intermolecular hydroamination reactions. In some cases high catalytic activities were achieved. Studies on the mechanism of the catalysis reactions revealed that the presence of a highly electrophilic zinc center is crucial for good catalytic performance.

This study analyzes the reactivity and selectivity of Friedel-Crafts alkylations using benzylic alcohols and phenols in the presence of a Lewis acid, to synthesize methoxylated bisphenols as a benign alternative to BPA. The degree of methoxylation on the electrophile appears to affect the yield of the reaction while the degree of methoxylation on the nucleophile appears to affect the selectivity. A more methoxylated electrophile results in a lower yield whereas a more methoxylated nucleophile results in a change in ratio between the bisphenol isomers and/or causes other isomers to form. Neither the yield nor the selectivity appears to be affected significantly by the temperature.