C2‐Symmetric Bicyclic Diols as Chiral Ligands in the titanate‐catalyzed enantioselective addition of alkylzinc reagents to aldehydes

Enantiomerically pure C2‐symmetric 1,4‐diols embodying bicyclic C‐frameworks were synthesized by means of asymmetric carbo‐Diels‐Alder reactions as key steps (Scheme 1). They were investigated as chiral ligands in the enantioselective addition of ZnEt2 to aromatic aldehydes. In the presence of 20–40 mol‐% of the titanates formed from these diols and [Ti(i‐PrO)4] at −78°, the respective 1‐arylpropanols were obtained with enantiomer ratios up to 93:7 (Scheme 2, Table).