Transition-metal-free semihydrogenation of diarylalkynes: highly stereoselective synthesis of trans-alkenes using Na2S·9H2O.

A highly stereoselective and efficient transition-metal-free semihydrogenation of internal alkynes to E-alkenes using cheap and green water as hydrogen donor is described. The reactions are conducted under convenient conditions and provide products in good to excellent yields, with broad substrate scope, including a variety of diarylalkynes.