Electroreductive 1,4-Hydro(deutero)arylation of 1,3-Enynes Enabled by Terephthalonitrile: Entry to Trisubstituted Allenes

An electroreduction method for regioselective 1,4-hydro(deutero)arylation of 1,3-enynes with aryl iodides and H₂O or D₂O has been developed, delivering diverse aryl-functionalized trisubstituted allenes under mild, transition-metal-free, and external reductant-free conditions. Upon the activation of terephthalonitrile as the organic electron transfer mediator, the protocol enables the formation of aryl radicals via single-electron transfer (SET) reduction with aryl iodides. The protocol shows a broad substrate scope with a good functional group compatibility and allows deuterium labeling using D₂O with up to 99% D-incorporation. Mechanistic studies support a cathodic radical anion-single electron reduction-cathodic radical polar crossover relay pathway, offering a sustainable approach to access trisubstituted allenes.