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Photoreactions have been of great interest amongst synthetic chemists for their powerful C-C bond-forming capability that are otherwise impossible under thermal, conventional heating conditions. Formation of C-C bonds via [2+2] cycloaddition, making cyclobutane rings, is an example of such a reaction. Since previously utilized irradiation of small organic molecules by UV light results in short-lived excited states and high-energy intermediates, it vital to exploit a visible light source to mitigate side-reactions and decomposition of cyclobutane formation. Recent reports outlines the use of photoredox catalysts or redox photosensitizers has shown that photocycloaddition reactions are possible under a lower energy system using visible light. Our work focuses on the energy transfer of iridium and ruthenium polypyridyl complexes (photoredox sensitizers) on a quinolone substrate, which has been previously reported to add to substituted alkenes in a [2+2] manner under UV light. By irradiating with visible light (λ=~390-700nm) these catalysts are likely to be excited to a state where they undergo redox transformations, activating the quinolone to form a radical ion which can subsequently undergo [2+2] cycloaddition. Mechanistic studies using cyclic voltammetry to determine the quinolone substrate’s reduction potential also has been conducted to observe its role in the photoredox cycle and radical propagation. Attempts to control the diastereoselectivity and enantioselectivity of this reaction via this method will subsequently be investigated.
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Shahid, Sabrina Mohammed, "Investigation of [2+2] Cycloadditions utilizing iridium and ruthenium polypyridyl photoredox catalysts" (2016). Senior Projects Spring 2016. 5.
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