SUPER · Synthetic Utilization of Photoredox-generated Electrophilic Radicals

Synthetic Utilization of Photoredox-generated Electrophilic Radicals

The greatest strength of the radical reactions lies in the possibility of executing them late in a synthetic route when the substrates usually have broad and dense functionalization. A downside of these reactions is that they commonly require the utilization of superstochiometric amounts of toxic organotin compounds. In fact, almost a decade ago, tin-free radical reactions were proclaimed by the ACS’s roundtable on green chemistry as one of the key areas of improvement in the synthesis of pharmaceuticals. With the advent of photoredox catalysis, tin-free opportunities of radical reactions emerged. This is reflected in the number of publications demonstrating that abundant low-energy visible-light together with an appropriate photoredox catalyst, can substitute organotin compounds and effectively mediate radical reactions. For organic chemists, it is of vital importance to explore and develop novel, less toxic and more user-friendly syntheses. It is crucial to realize that if a chemical process is useful throughout the academic and industrial sectors, it produces significant amounts of toxic waste, which is most of the time incinerated. In the proposed research, we aimed to develop a practical and scalable radical synthesis of small heterocycles, that would be free of organotin compounds. We envisioned a formal [3+2] cycloaddition of azahomoallyl radicals and olefins. A critical aspect would be the generation of a heteroatom-centered radical, which could potentially undergo two different elemental processes – addition or abstraction of hydrogen. While both of these reactions take place during the radical reactions, a theoretical framework that would allow chemists to predict when each step is favored is still missing. We aimed to explore if the electrophilicity of nitrogen-centered radical effects the preference of addition and abstraction of hydrogen.

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