| Summary: | The research in this thesis is focused on new intermolecular additions of diverse nucleophiles to allenic and bisallenic motifs catalysed by transition metals. In the first project we developed a new Au-catalysed azidation of allenes for the synthesis of functionalised allylic azides, which are important precursors to many functional groups. A cationic Au(I)-catalyst was found as a suitable activator for the allenic π-system favouring the attack of challenging azides as nucleophiles and giving access to the desired allylic azides. Deuterium-labelling experiments revealed that the reaction goes via a vinyl gold intermediate, which allowed an orthogonal functionalisation of the allenes, using as electrophile iodine to break the Au-C giving valuable iodo-alkenyl azides. Besides, preliminary mechanistic studies by NMR disclosed a possible inner-sphere mechanism with the formation of Au-N3 complexes with a continuous exchange of counterions involved in the reaction. The second part of the present thesis was aimed to develop a novel platinum-catalysed carbo- and heterocyclization of 1,5-bisallenes to obtain 6- or 7-membered rings with and extra oxygen functional group incorporated in the skeleton of the molecule. These cyclic compounds are interesting building blocks encountered into the core of several natural products, especially in terpene and sesquiterpene family. Cationic Pt(II)-catalysts with electron-withdrawing ligands were found appropriate to lead the ring closing of these 1,5-bisallenes. The reaction seems to be triggered by the attack of oxygen nucleophiles to the activated terminal π-system of the bisallene showing different coordination modes, which give access to isomeric 6- or 7-membered rings. Deuterium labelling and preliminary mechanistic experiments revealed, that the formation of the products goes via a vinyl platinum intermediate in the different cyclization modes. Besides, the reaction has been monitored by 1H NMR in order to study the decomposition level of the bisallenes under catalytic conditions and the possible interconversion between the isomeric cyclic products.
|
|---|
