Synthesis of a C2‐Symmetric Chiral Bipyridyldiol Ligand and Its Application in the Enantioselective Addition of Diethylzinc to Substituted Benzaldehydes.

Abstract

Abstract Herein the synthesis of a novel C 2 -symmetric ligand comprising of a central bipyridine-pinene-derived core and two functionalized diphenylmethanol subunits is described. [8′-(Hydroxy-diphenyl-methyl)-10,10,10′,10′-tetramethyl-[5,5′]bi[6-aza-tricyclo[7.1.1.0 2,7 ]undecyl]-2(7),3,5,2′(7′),3′,5′-hexaen-8-yl]-diphenyl-methanol 10 is a suitable catalyst for the enantioselective addition of dialkylzinc to various aromatic aldehydes with asymmetric inductions of up to 99% ee. Importantly, the correlation of Hammett substituent constants and enantiomeric excess, with the electron-donating group at the para -position and the electron-withdrawing group at the meta -position of substituted benzaldehydes were demonstrated to give high enantioselectivity in alkylations using diethylzinc.