New gold(I)-catalysed cascade reactions for the synthesis of pentannulated N-hetero- and carbacycles

This thesis work aims at the development of new gold(I)-catalysed tandem processes for the synthesis of pentannulated N-hetero- and carbacycles in a highly efficient manner. The general approach entails an initial Claisen rearrangement, through which an allene-gold(I) complex is formed as intermediate, and a final cyclisation of the latter. Depending on the substrate, different catalysts have been evaluated in order to promote the second step of the tandem process. While with carba- and N-heterocycles the reaction occurs with most of phosphine and carbene ligands (chapter 3), when using aromatic substrates only a carbene ligand (IPr) turned out to be efficient for the final cyclisation (chapter 5). This tandem process was further implemented by adding another step to the cascade. In fact, the pentannulated products were in situ elaborated through Grignard, Wittig and Diels-Alder reactions (chapter 4), exploiting the aldehyde functionality and/or the diene system. In this way, we performed at least three reactions in one-pot, achieving the synthesis of complex compounds under mild conditions, in short times and with good to excellent yields. This approach was then applied to the total synthesis of a target compound, epi-Jungianol (Chapter 6). By employing the presented methodologies, two almost equivalent routes were accomplished, thus demonstrating the usefulness of our tandem process. Finally, during a secondment activity in the group of Prof. A. M. Echavarren at the Catalan Institute of Chemical Investigation (ICIQ), the design and the synthesis of new gold(I) cavitand catalysts were studied (chapter 7). Moreover, the activity of some resorcinarene-based gold(I) catalysts was investigated through alkoxycyclisations of dienynes, obtaining promising results.