Optically Active Helical Poly[(S)-3-vinyl-2,2′-dihydroxy-1,1′-binaphthyl]: New Ligand for Asymmetric Addition of Diethylzinc to Aryl Aldehyde

Poly[(S)-3-vinyl-2,2-dihydroxy-1,1-binaphthyl] (L*) was obtained by taking off the protecting groups of poly[(S)-3-vinyl-2,2-bis(methoxymethoxy)-1,1-binaphthyl] (poly-1). L* was proved to keep a stable helical conformation in solution. The application of helical L* in the asymmetric addition of diethylzinc to aldehydes has been studied. The catalytic system employing 10 mol% of L* and 150 mol% of Ti((OPr)-Pr-i)(4) was found to promote the addition of diethylzinc to a wide range of aromatic aldehydes, giving up to 99% enantiomeric excess (ee) and up to 93% yield of the corresponding secondary alcohol at 0 degrees C. The chiral polymer can be easily recovered and reused without loss of catalytic activity as well as enantioselectivity.