Visible-Light-Driven α‑Allenylic C–O Bond Cleavage and Alkenyl C–S Formation: Metal-Free and Oxidant-Free Thiolation of Allenyl Phosphine Oxides

A visible-light photoredox cleavage of α-allenylic C–O bond and alkenyl C–S formation is disclosed for the first time. The thiolation of allenyl phosphine oxides with diaryl disulfides occurs smoothly in metal-free and mild conditions, affording novel S,P-bifunctionalized butadienes with moderate to excellent yields. Mechanistic studies explain the cleavage of a C­(sp³)–O­(Ar) bond in initiating a key alkenyl radical intermediate.