Photoelectrochemically Driven Hydrophosphorylation of Alkynes to Access ( E )‐Alkenylphosphine Oxides

The current metal‐free methods for the hydrophosphorylation of alkynes, encompassing both electrochemical‐driven and photoredox‐catalyzed processes separately, show efficacy only when applied to less hindered terminal alkynes, polarized internal alkynes, or aryl alkyl internal alkynes; diaryl acetylenes are found to be incompatible with these conditions. Both methods involve a radical stepwise addition, yielding a Z / E isomeric mixture with the Z ‐alkenylphosphine oxides as the primary products. Furthermore, electrochemical hydrophosphorylation of alkynes is prone to double reduction of alkynes during extended reaction times. Herein, in sharp contrast to conventional, often separate, electrochemical or photoredox catalytic approaches that typically produce a Z / E isomeric mixture, this photoelectrocatalytic (PEC) process, which combines photocatalysis and electrochemistry, exclusively furnishes stereospecific ( E )‐alkenylphosphine oxides as the sole products. Significantly, this protocol successfully applies efficiently to diaryl acetylenes and bulky terminal alkynes, with no iterative addition of triple bonds observed.