Photochemical Strategies for Carbon-Carbon Bond Forming Processes

The chemical reactivity of electronically excited molecules differs fundamentally from that in the ground state. An excited-state molecule is both a better electron donor and a better electron acceptor than in the ground state and behaves respectively as a better reductant and a better oxidant.

The main scientific objective of this doctoral research was to investigate and understand the excited-state reactivity of some organic molecules to develop novel photochemical C–C bond-forming processes. In order to achieve this goal, different tools of organic chemistry were combined.

In the first projects, we demonstrated that transiently generated chiral iminium ions, which are key intermediates in polar enantioselective organocatalytic processes, can enable previously inaccessible reactivities when reaching an excited state upon visible-light absorption. We applied this photochemical mode of substrate activation to develop enantioselective β-benzylations and β-alkylations of enals.

Furthermore, we have documented that 4-alkyl-1,4-dihydropyiridines can unveil a rich photochemistry upon light excitation. Selective absorption of violet light turns them into strong reducing agents that can activate reagents via single-electron transfer manifolds while undergoing a homolytic cleavage to generate C(sp3)-centered radicals. This light-triggered dual reactivity profile was integrated with transition metal catalysis for the development of nickel-catalyzed radical cross-couplings.