Sustainability of chemical processes is an incredibly important part of the pursuit for overall sustainability of modern economy. Harnessing the power of light and transforming it through an efficient photocatalytic manifold has recently become a major focus of research in the field of organic chemistry. In this thesis, the synthetic potential of photocatalytic strategies is employed to selectively forge new C(sp²)-C(sp³) and C(sp³)-C(sp³) bonds. Specifically, single-electron reduction of electron-deficient π-systems was exploited as a means of achieving unconventional reactivity.

First, a new strategy for the regioselective radical functionalization of pyridines and related heteroarenes is described, enriching the radical-based chemistry of pyridines. This strategy is enabled by the formation of previously neglected pyridinyl radicals, obtained in a catalytic manner via single electron transfer (SET) reduction of pyridinium ions. Key to the design of this protocol was the use of the dithiophosphoric acid catalyst, which served three distinct roles during the reaction, sequentially acting as a Brønsted acid for pyridine protonation, an SET reductant of pyridinium ions upon light excitation, and a HAT acceptor for the allylic C-H bonds upon formation of the thiyl radical.

In the second project, a new light-driven strategy for the reductive olefin cross-coupling has been detailed, providing sp3-rich products with a distinct connectivity starting from broadly available olefin substrates. Central to this strategy was the exploitation of the electronic differences between the two olefin partners, enabling selective radical generation via photoredox-mediated SET reduction of the electron-deficient olefins. Overall, the electron-poor substrates were readily coupled with various styrenes and other electron-neutral olefins, finally undergoing reduction via HAT process mediated by a thiol catalyst. A notable feature of this method is its high functional group tolerance, which was leveraged for the late-stage modification of biorelevant compounds.

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