Combining Iminium Ion-Mediated Catalysis and Photochemistry to Develop Enantioselective Radical Processes

Identifier:  TDX:3087

Handle: https://hdl.handle.net/20.500.11797/TDX3087

Authors:  Bonilla Dominguez, Pablo

Abstract:
The main scientific objective of my doctoral studies was to demonstrate the potential of organocatalysis to make chiral molecules with high stereoselectivity using the reactivity of photochemically generated radicals. These open-shell intermediates were generated by two different approaches: i) upon direct excitation of organocatalytic intermediates while exploiting the ensuing single-electron-transfer mechanisms, or ii) by using an external photoredox catalyst. Radical were then intercepted by chiral organocatalytic intermediates with high stereocontrol. As detailed in Chapter III, I first developed an asymmetric photochemical radical cascade process. Our system harnesses the oxidative potential of visible-light excited chiral iminium ions to activate alkenes, which are generally recalcitrant to thermal activation strategies, and form reactive radicals that trigger a stereocontrolled cascade. After establishing that excited-state chiral iminium ions could successfully oxidize unactivated alkenes, we wondered if a similar strategy could be expanded to the underexplored activation of allenes. Chapter IV details the successful development of a visible-light-driven enantioselective organocatalytic process involving difficult-to-control allene radical cations Chapter V details our efforts to establish a general procedure for the enantioselective radical conjugate addition to simple α,β-unsaturated aldehydes. We envisioned that employing an external photocatalyst as an oxidant to generate a radical, we could intercept the radical with an electrophilic ground-state chiral iminium ion.