In dieser Arbeit wird durch Modellrechnungen gezeigt, wie die Stickstoffinversion in Azacyclen als molekularer Schalter genutzt werden könnte. Hierzu werden ein Fluorazetidin- und ein Fluorazacyclopentanderviat quantenchemisch untersucht. Das letztere Molekül wird auch quantendynamisch untersucht. Jedes der beiden Moleküle besitzt zwei stabile Konformationen. Es wird gezeigt, dass das Azabicyclopentanderivat von der einen Konformation mittels zweier linear polarisierter IR-Laserpulse durch sogenanntes “ladder climbing” in die andere überführt werden kann. / In this work it is shown by model simulation, how the nitrogon inversion in azacycles could be used as a molecular switch. For this a azetidine derivative and a fluoroazabicyclopentane derivative have been investigated quantumchemically. Both of the molecules have two stable conformers. The latter molecule is also investigated quantumdynamically. Its is shown that the azabicyclopentanederivative can be switched from one conformer to the other by using two linear polarised IR laser pulses via ladder climbing.

The work presented in this thesis involves new transformations of azacycles, focusing on the introduction of functionality α-to N. α-C-H functionalisation on an azetidine has been a long-standing challenge, with N-protecting/activating groups that work well in the higher and lower azacyclic systems not viable. A recent breakthrough in the Hodgson group showed the rarely used N-thiopivaloyl group was effective for α-deprotonation– electrophile trapping on azetidines, but was not without limitations concerning harsh removal conditions and scope for further substitutions. This thesis describes efforts to overcome these issues by development of a new protecting/activating group for N, t-butoxythiocarbonyl (Botc).

This thesis describes our examination of the reactivity of allenylpalladium intermediates generated from the reaction of palladium(0) with propargylic electrophiles. Chapter 1 provides a general overview of the literature reported to date concerning the nature and reactivity of allenylpalladium intermediates. The coupling of a variety of propargylic electrophiles with aryl boronic acids to form allenes is examined in Chapter 2. However, when employing diastereomerically pure electrophiles, some erosion of stereochemistry was observed in the allene products. This effect was examined further, and epimerisation of the allene product was found to be the origin of the loss of stereochemistry. Evidence for the species likely responsible for this epimerisation is presented. The serendipitous formation of tetrahydrofurans (THFs) from propargylic 7-membered cyclic carbonates prompted an in-depth examination of this reactivity, as described in Chapter 3. The reaction of these cyclic carbonates was rendered stereoselective and the stereochemical outcome of the reaction elucidated. The methodology was extended to propargylic acyclic carbonates which allowed the formation of tetrahydropyrans (THPs). The effect of ring-size and substituents on the cyclisations was examined, culminating in the formation of two rings in a single step from diol-containing bis-carbonates. Chapter 4 describes the extension of this methodology to the formation of azacyclic products. This built upon foundation work conducted by a Part II student within the group, and further improved the selectivity of the reaction. Two diverse azacyclic skeletons could be formed from the same substrate by the employment of different bidentate phosphine ligands, and a variety of substrates were examined under these conditions. Chapter 5 draws general conclusions and sets out possible future directions for the methodology, and full experimental details are outlined in Chapter 6.