Formal Olefinic C−H Phosphinylation via Alkenyl Sulfonium Salts

Formal olefinic C−P cross‐coupling between alkenyl sulfonium salts and secondary phosphine oxides and H‐phosphinates has been developed. A base enables construction of alkenyl C−P bonds as well as aliphatic C−P bonds at ambient temperature under an air atmosphere. This protocol provides an alternative access to multisubstituted alkenyl phosphine oxides and phosphinates in 40–99% yield from functionalized alkenes through an interrupted Pummerer activation/base‐promoted olefinic C−S bond phosphinylation sequence. Gram‐scale preparation and feasible derivatization demonstrated the applicability of the resultant alkenylphosphine oxides.