AbstractCopper‐catalyzed CP cross‐coupling reactions between diphenylphosphine oxide and various 1‐bromo‐1,3‐butadienes readily provided a set of functionalized 1,3‐butadienyldiphenylphosphine oxides. Application of the latter to the synthesis of stereodefined 1,3‐butadienyldiphenylphosphines was successfully achieved via chemoselective reduction of their phosphoryl moiety.magnified image