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 -> BF 4 -≈ PF 6 -. 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.

Phosphonium Ion-Tethered Secondary Amines for Chemospecific 5-Enolexo Aldol Condensations of 6-Ketoaldehydes

“… We anticipated that the oxophilic phosphonium ion within catalyst 1 would enhance selectivity by stabilizing intermediate transition states through Coulombic interactions between phosphonium and carbonyl oxygen. Importantly, these proline derivatives with methylphosphonium ion substitution had not previously been reported …”

4‐Methyltetrahydropyran: A Versatile Alternative Solvent for the Preparation of Chiral BINOL Catalysts and the Asymmetric Alkylation of Aldehydes

“…The authors have cited additional references within the Supporting Information (Ref. [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50]).…”

Chemo- and Enantioselective Addition and β-Hydrogen Transfer Reduction of Carbonyl Compounds with Diethylzinc Reagent in One Pot Catalyzed by a Single Chiral Organometallic Catalyst

“…By increasing the use of the diethylzinc reagent, the addition product was obtained with almost the same level of yield and ee , but the enantioselectivity of the reduction product decreased significantly (Table , entry 2). For the asymmetric ethylation reaction, the addition reaction between benzylaldehyde and the diethylzinc reagent is very slow in the absence of the chiral ligand. − However, for the asymmetric β-hydrogen transfer reduction, the diethylzinc reagent can reduce the α-trifluoromethyl ketone without the chiral ligand. − Therefore, an excessive amount of the diethylzinc reagent has a great influence on the enantioselectivity of the asymmetric β-hydrogen transfer reduction while it has little effect on the asymmetric ethylation. When 2.0 equiv of the diethylzinc reagent was used, the yield of the reduction product was only 67% with 65% ee (Table , entry 3).…”