In the last decade two areas have emerged in organic synthesis with special impact in the research community: metathesis and organocatalysis. Both methodologies have in common that had passed unnoticed for years despite their potential and only very recently those areas have witnessed an extraordinary rebirth. The enormous attention that scientists have paid to them is due to the wide range of possibilities they offer in synthesis, metathesis processes in the creation of C=C bonds and organocatalysis in asymmetric synthesis starting from achiral precursors. Therefore, these methodologies captured our attention and we decided to get involved in those areas of research. Thus, the research performed during my thesis can be divided into two main parts: a) tandem or cascade processes being one step a metathesis reaction and b) enantioselective synthesis of nitrogen-containing compounds through organocatalysis.
      
      The first half consisted of two tandem processes, RCM-isomerization and CM-intramolecular aza-Michael reactions. Although the first one was already known we found that is possible to carry out the protocol employing the 2nd generation Grubbs catalyst without the use of additives. The influence of F in the overall process was also investigated. The second one instead, was studied in our group for the first time employing ruthenium metathesis catalyst.
      
      In the second half, we developed two enantioselective reactions for the synthesis of fluorinated aminoalcohols and nitrogenated heterocycles through organocatalytic Mannich and intramolecular aza-Michael reactions respectively. In both cases catalysts of choice were proline itself or proline derivatives.

      Finally, the developed methodology is applied for the asymmetric synthesis of three piperidine alkaloids.