Alternative approaches to heterocyclic compounds through new developments of domino transition-metals catalysed and/or Lewis acids promoted reactions

The aim of the project is based on the development of alternative synthetic methodologies in order to obtain heterocyclic compounds of interest in biological and pharmacological fields. In particular, homogeneous and heterogeneous transition-metal catalysts and/or Lewis acids will allow the development of domino and multi-component reactions devoted to the preparation of heteropolyciclic rings through domino coupling/regioselective annulation reactions starting from alkynes/alkenes containing proximate nucleophiles as suitable building blocks. Among the variety of new synthetic transformations, transition metal-catalysed reactions are some of the most attractive methodologies for synthesising heterocyclic compounds, because a transition metal catalysed reaction can directly construct complicated molecules from readily accessible starting materials under mild conditions. Moreover, organometallic intermediates are useful for synthesising organic compounds which are difficult to obtain through traditional methods and/or are responsible for regio-, stereo-, and chemoselectivity. In contrast with classical synthetic procedures which involve multistep synthetic operations, transition metal-catalysed reactions are often domino processes which lead to the facile creation of several new covalent bonds in a one-pot procedure or can accomplish the coupling of three or more simple and flexible building blocks in a multicomponent reaction. Besides, starting from suitable and reactive substrates, domino transformation can be easily achieved under mild reaction conditions without catalysts, in presence of Lewis acids or promoters that can act both as Lewis acids and transition metals. Many new procedures based on transition metal complexes or other suitable catalysts have been developed to obtain heterocycles by C-C and C-N bond formation with maximal conversion of the reagents and minimal generation of by-products starting from substrates that are readily available and generally easy to handle. In the field of metal catalysed-reactions our research group focused the attention toward the families of transition metals and Lewis acids. In the first case we were attracted by the high versatility and activity of palladium, rhodium, and gold salts and complexes in cross-coupling reactions and multiple bonds activation. Moreover, we considered the family of Lewis acids using titanium, indium and gallium salts with their feature to activate both carbon-carbon and carbon-heteroatom multiple bonds. Moreover, metal-mediated reactions have been mainly applied to the domino/multicomponent synthesis of heterocyclic compounds from substrates characterised by the presence of an alkyne and a proximate nucleophile. These compounds demonstrated to be suitable building blocks for the synthesis of relevant heterocyclic scaffolds.