Cycloisomerization reactions catalyzed by transition metal complexes. Synthesis of oxygen- and nitrogen- containing heterocyclic compounds.

The increasing need for environmentally responsible means of preparing a wide diversity of chemical products demanded by society drives the quest for synthetic efficiency. Transition metal-catalyzed cyclizations of polyunsaturated system, which are both selective and atomeconomical, represent an important starting point for this long-term goal. We describe herein four different class of transition metal-catalyzed reactions that provided an atom- and step-economical entry into a range of oxygen- and nitrogen-containing heterocycles: (1) ring-closing metathesis, (2) Pauson-Khand reactions, (3) platinum-, goldand iridium-catalyzed electrophilic activation of alkynes and (4) gold-catalyzed cyclizations of allenes. All these transformations allow for a rapid increase in molecular complexity from relatively simple starting materials. Moreover, since these processes exhibit an excellent chemoselectivity towards C-C ! systems, the cyclized products usually retain different functional groups that can be used for further synthetic transformations. Manuscripts adding to the scope of transition metal-catalyzed reactions are being published at a rapid rate attesting to their interest in the chemical community. With the development of new asymmetric methodologies, the transformations described in this thesis will continue to occupy, in the next future, a remarkable role in organic synthesis.