Publication
Alcohols are ubiquitous in nature and are present in a wide range of biomass-derived compounds, including sugars, lignin monomers, and amino acids. As a result, they offer significant potential as substrates for the development of new transformations, particularly those focusing on the homolytic cleavage of the C-O bond. Photochemistry has emerged as a highly effective tool for synthesizing complex molecules in a step-economical manner under mild reaction conditions. Moreover, the formation of open-shell species through photochemical methods allows for complementary reactivity to polar processes, while maintaining a high functional group tolerance. Alkynes are versatile functional groups, valued for their ability to serve as rigid linkers or to be transformed into other functionalities. Consequently, they find numerous applications across various fields, including medicinal chemistry, chemical biology, and materials science. Among the various radical approaches developed over the years to access alkynylated compounds, ethynylbenziodoxolones (EBXs) have proven to be efficient radical traps. The first goal of this research was to develop a photoredox catalyzed deoxyalkynylation reaction from easily accessible tertiary cesium oxalates using EBX reagents as radical traps and an organic dye as photocatalyst. The key for the success of the transformation was the use of high intensity blue light irradiation, more precisely two Kessil lamps (440 nm, 44 W each), which, alongside the use of 4CzIPN as photocatalyst, ensured high yield and broad scope. During our investigations, we also discovered that, in absence of the photocatalyst, the high intensity irradiation could generate the excited state PhEBX species. The latter is able to act as photooxidant in the reaction, providing the desired product; hence alleviating the need for the photocatalyst. We were pleased to see that excited PhEBX was able to oxidize various functional groups, such as carboxylates, trifluoroboronates, enamines and imines; as well as performing a-oxo C-H alkynylation. The second goal of this thesis was to develop an organic dye photocatalyzed synthesis of lactones and lactams. Here, we used homoallylic cesium oxalates and oxamates which, after oxidation from the photocatalyst and successive decarboxylation, form an acyl radical intermediate. The latter undergoes fast 5-exo-trig cyclization onto the olefin and the radical is then trapped by an EBX reagent, forming the alkynylated product. With this strategy, we were able to form various spirocyclic compounds as well as fused and bridged bicyclic lactones. Because sugars are one of the most abundant alcohol feedstocks, the third goal of this research was to develop a photocatalyzed synthesis of C-glycosides by in situ alcohol activation. Unfortunately, this transformation remained elusive. Finally, in our fourth project, we established a collaboration with the group of Prof. Raffaella Buonsanti on the use of colloidal quantum dots f