Development of novel synthetic methodologies in photocatalysis

Abstract

The last decade has seen an impressive number of studies in the field of photocatalysis: the mild conditions used for the generation of radical intermediates and the possibility to couple it with other catalytic manifolds are among the reasons of such popularity. In this thesis, the use of some photocatalytic strategies in organic synthesis is presented. The development of a dual Ni-photoredox strategy for the asymmetric synthesis of N-benzylic heterocycles, interesting drug-like compounds, is described in Chapter 2: a privileged ligand system was found for inducing chirality, and the effect of different heterocycles (in particular bearing directing groups) was addressed. A different perspective is taken in Chapter 3: in this case the focus is not on the transformation, but on PXX (peri-xanthenoxanthene) as a new photocatalyst. Possessing a relatively high reduction potential in the excited state, PXX is capable of promoting a variety of reactions, from the addition of aryl radicals to radical traps, to the organocatalytic β-arylation of cyclic ketones, to Ni-catalysed carbon-heteroatom cross-couplings. The focus moves to organocatalysis in Chapter 4, in particular to the use of chiral iminium ions as photoredox-active species: paired with 4-alkyldihydropyridines as radical precursors, an asymmetric β-alkylation of enals is thus demonstrated. ii Chapter 5 takes back themes encountered in the previous chapters to briefly introduce some attempted but not successful transformations: an organocatalytic β-fluorination of aldehydes, and a cross-coupling strategy towards an API intermediate