Selectivity emerges from indiscriminate photoreduction

Single electron transfer (SET) reduction is among the most fundamental strategies for the activation of organic compounds. The design of selective reactions that leverage SET is grounded by the premise that differences in substrate redox potentials predict relative rates of SET, with more favourable reductions occurring faster¹. However, across the diverse modes of redox catalysis^2,3, devising reactions that require SET to the harder to reduce of two reactants remains challenging. This restriction all but precludes coupling reactions when targeting substrates that are thermodynamically difficult to reduce or oxidize^4,5. Here we introduce an alternative selectivity manifold for outer-sphere SET that is divorced from substrate redox potentials. We show that super-potent photoreductants render substrate redox potentials irrelevant through diffusion-limited SET, allowing a new selectivity profile to emerge from competition between downstream chemical steps and back electron transfer (BET). We validate these principles in the context of radical annulation reactions between cyclopropyl ketones and easier-to-reduce alkenes. Although these mismatched redox potentials previously precluded these reactions, we promote selective radical annulation even as the requisite ketone reduction becomes disfavoured by a volt. More broadly, these studies offer a general blueprint for the design of SET reactions that require violation of redox potential control.