HETEROHELICENES AS APPEALING CHIRAL SYSTEMS: INNOVATIVE METHODOLOGIES FOR THEIR PREPARATION ALSO IN ENANTIOMERICALLY PURE FORM

Helicenes are ortho-annulated polycyclic aromatic or heteroaromatic compounds, endowed with inherent chirality owing to the helical shape of their π-conjugated system. Carbohelicenes only include benzene rings in their structure, while in heterohelicenes one or more heterocycles are present. Interestingly, the introduction of heteroatoms into the fused polycyclic frameworks adds remarkable changes to the electronic structures of helicenes, and additional chemical and physical properties. Their unique structural features and physicochemical properties have stimulated manifold studies in several fields, including optoelectronics, material science, asymmetric catalysis, and chiral recognition. Many of these applications require the use of enantiomerically pure helicenes, although the resolution of racemates by means of analytical methods as well as the separation of diastereomers still remain the most common ways to obtain non-racemic helicenes, whose peculiar geometry makes them extremely difficult targets for stereoselective synthesis. This Ph.D. thesis was intended to provide a meaningful contribution in the development of innovative and versatile syntheses of heterohelicenes, also in enantiopure form, and has focused on the following main goals: 1. Study of methodologies for the synthesis of functionalised tetrathia[7]helicenes (7-THs). 2. Synthesis of different classes of thiahelicenes through methodologies set up for the preparation of 7-THs. 3. Enantioselective synthesis of thia[5]helicenes via Au-catalysed alkyne hydroarylation. In the course of this thesis, a sub-topic has also been developed: 4. Functionalisation of benzo[1,2-b:4,3-b']dithiophenes by Suzuki reactions in Deep Eutectic Solvents (DESs).