Final Report Summary - MCCYC (Metal catalyzed strategies for C-H bond activation and cycloaddition. Synthetic applications and discovery of non conventional transformations) This research project titled 'METAL CATALYZED for C-H BOND ACTIVATION and CYCLOADDITION. SYNTHETIC APPLICATIONS and DISCOVERY of NON-CONVENTIONAL TRANSFORMATIONS (MCCYC) ', have been mainly focused on the development of a new efficient straightforward access to the N-heterocyclic molecules such as indolizinones, isoquinolones or pyridines -which are the core of biologically active molecules and key features on many pharmaceuticals- allowing the direct access to libraries of compounds for medicinal chemistry. These bioactive structures as well as most of the organic molecules, materials and fuels are made from a carbon based, mostly bonded to one or more hydrogen atoms. In order to create the new C-C bonds needed to accomplish their synthesis, chemists generally rely on the participation of functional groups or structural features exhibiting relatively high chemical complexity and reactivity. Unfortunately, in order to incorporate these functional groups several synthetic steps are very often needed, leading to non-practical lengthy synthetic routes. The methodologies developed in this research are devoted to overcome these limitations. In particular, the work was focused on a different and more direct approach based on the activation of simple C-H bonds -which are largely present in most of the raw materials and until recently has been seen as unreactive chemical bonds- or cycloaddition reactions catalyzed with transition metal complexes. Several new transformations leading to the formation of cyclic compounds were developed where new C-C or C-N bonds were created in just one step from simple materials. Therefore, these methodologies led to a shortening of the synthetic routes and therefore contribute to decrease their economic cost and the environmental footprint. Even more alluring, these methodologies bring new and original retrosynthetic disconnections, which would greatly expand the number of available pathways to build complex molecular scaffolds. The activation and functionalization of these C-H bonds have been possible thanks to the chemical abilities of transition metal complexes. Together with known commercial available Rh(III)-catalysts, new Ruthenium and Osmium catalyst metals have been studied in this research, leading to the discovery of new efficient transformations. In the future these organometallic compounds could be applied to new reactions based on C-H activation processes, cycloaddition or other highly valuable transformations. In summary, the research developed in this project, based on metal catalyzed C-H bond functionalization and cycloaddition reactions, will have a great impact in the chemical community because meets the ideals of green chemistry, while providing a direct access to highly valuable bioactive cores.