Phosphonium Salt Catalyzed Addition of Diethylzinc to Aldehydes

Abstract

The addition of diethylzinc to aromatic, heteroaromatic, and aliphatic aldehydes at room temperature is efficiently catalyzed by 1-7 mol% tetrabutylphosphonium chloride. The corresponding addition products are obtained in good to excellent yields of up to 99%. Moreover, polymer bond phosphonium salts can be used to catalyze this reaction with excellent recovery of the polymer bond catalyst up to three cycles. The application of chiral bifunctional phosphonium salts revealed a remarkable counter anion effect. Changing the anion, the activity of the tetrabutylphosphonium salt decreased in the order Cl- > Br- > I- ≈ TsO- > BF4 - ≈ PF6 -. However, the nature of the cation had also significant influence. Tetraalkyl­ammonium chlorides showed similar activity compared to phosphonium chlorides, while alkaline metal chlorides proved to be considerably less active.