Electrolyte-Guided Selectivity Unlocks Pathway Control in Electrochemical Olefin Functionalization.

Organic electrosynthesis offers a direct, electricity-driven strategy for constructing complex molecular structures in a more sustainable and innovative manner. However, even with the precise redox control that electrochemistry affords, steering highly reactive intermediates along a single productive pathway remains a central challenge, particularly when multiple mechanistic manifolds are accessible. Herein, we demonstrate that the identity of the supporting electrolyte dictates the selectivity of electro-reductive olefin coupling, directing the transformation toward either exclusively linear or exclusively branched products. Radical probes, CV, SEM, ssNMR, EPR, and DFT clarify these distinct pathways. Ammonium salts preserve the terminal spin bias of the styrene radical anion, promoting solution-phase radical addition for linear products. Lithium salts instead form a Li-rich interphase that drives benzylic spin localization and channels surface-confined radical coupling to yield branched products. This platform streamlines access to pharmaceutical-relevant scaffolds and reveals previously underexplored polar hydrofunctionalization of conjugated olefins. These findings establish electrolyte-controlled interfacial organization as a powerful lever to control product selectivity in organic electrosynthesis.