DEVELOPMENT OF PRECIOUS METAL-FREE, LIGHT-ENABLED SYNTHETIC METHODOLOGIES

In recent years, there has been a growing interest in the development of more sustainable and eco-friendly methodologies in the field of organic synthesis. The use of light is particularly attractive not only because light is a traceless and abundant form of energy, but also because the absorption of photons can undisclose several reaction pathways which could not be accessed otherwise. However, in many cases light is not absorbed directly by the substrates of the reaction, but an external photocatalyst is needed. For some years, the huge majority of photocatalyzed reactions used organometallic complexes, whose properties made them very attractive. On the other hand, since the natural abundance of these metals is limited and their cost is constantly increasing, it would be highly desirable to replace them with cheaper and readily available alternatives. In this thesis, it is shown how Donor-Acceptor (D-A) cyanoarenes can be regarded as effective replacements for noble metal-based photocatalysts. This has been done for the β-functionalization of carbonyl compounds, which has been realized through a fully organocatalytic methodology. At the same time, a “metallaphotoredox” C-O and C-N cross-coupling methodology has been developed combining a base metal (nickel) with donor-acceptor cyanoarene photocatalysts. Moreover, my work demonstrated that the D-A cyanoarenes can be conveniently incorporated into bifunctional photocatalysts able to bind transition metals. In particular, by comparing two such bifunctional systems with the corresponding dual catalytic systems in Ni-catalyzed C-O and C-N cross-coupling, it was demonstrated that a proximity effect is in place, from which the reaction could benefit. Finally, the use of UV light as a high energetic source of photons has been shown to activate aryl fluorides towards substitution with aryl rings and phosphinates. The latter reactions were carried out using flow conditions, showing the benefit that this technique can give to photocatalysis, ensuring an easy scale up and limiting the reaction time.