Stereo-reversed E2 unlocks <i>Z</i> -selective C–H functionalization

The stereoselective functionalization of C-H bonds represents a central challenge in modern organic synthesis. Despite decades of innovation in C-H activation chemistry, methods for <i>Z</i>-selective functionalization of alkenes have eluded synthetic practitioners. Terminal alkenes present the biggest challenge for <i>Z</i>-selectivity as they require selective cleavage of the more hindered of two otherwise virtually identical C-H bonds. Herein, we describe the transformation of alkenes into transient 1,2-<i>bis</i>-sulfonium intermediates found to undergo <i>Z</i>-selective elimination, overturning a textbook E2 stereoselectivity rule through stabilizing interactions. We identify paired electrolysis as an enabling strategy to both selectively generate the requisite <i>bis</i>-sulfonium intermediate and drive its rapid elimination in situ. The resultant <i>Z</i>-alkenyl sulfonium linchpins provide access to a wide array of <i>Z</i>-alkene targets from inexpensive feedstocks through robust cross-coupling reactions.