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).