Selectivity Emerges from Indiscriminate Photoreduction

Single electron transfer (SET) reduction is amongst 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 favorable reductions occurring faster.1 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 paradigm 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. While these mismatched redox potentials previously precluded such reactions, we promote selective radical annulation even as the requisite ketone reduction becomes disfavored by a volt. More broadly, these studies offer a general blueprint for the design of SET reactions that require violation of redox potential control.