1,4-Reduction of α,β-Unsaturated Ketones Catalyzed by Tetraarylhydrophosphoranes

We demonstrate that a pentavalent phosphorus compound, tetraarylhydrophosphorane, is capable of catalyzing 1,4-reduction of α,β-unsaturated ketones in the presence of pinacolborane. The structure and properties of tetraarylhydrophosphorane and its participation in the chemoselective 1,4-reduction were elucidated through both experimental and theoretical approaches.