Changes of enantioselectivity with the substrate ratio for the addition of diethylzinc to aldehydes using a catalyst coupled to a soluble polymer

Abstract

α,α-Diphenyl-L-prolinol, when coupled to a polymer soluble in organic solvents, gives surprising results for the addition of diethylzinc to aldehydes. For benzaldehyde, the enantiomeric excess strongly depends on the initial substrate ratio: an excess of diethylzinc yields (S)-1-phenylpropanol with up to 80% ee, while an excess of benzaldehyde leads to the (R)-1-phenylpropanol with up to 50% ee. The kinetic properties of the catalyst and the results with other aldehydes are also described. The polymer 1 is a copolymer of octadecyl methacrylate and 2-hydroxyethyl methacrylate.