Enantioselective addition of diethylzinc to aldehydes catalyzed by titanium(IV) complexes of N-sulfonylated beta-amino alcohols with four stereogenic centers.
An N-sulfonylated beta-amino alcohol (R,S,S,R)-9 with four stereogenic centers is prepared. The titanium complex of 9 is an effective catalyst to induce excellent enantioselectivities for diethylzinc addition to aromatic aldehydes with ee values up to 99%. The feature of doubling the quantity of Ti(O-i-Pr)4 required relative to the catalytic system of the Ti complex of bidentate N-sulfonylated beta-amino alcohols suggests that the two N-sulfonylated beta-amino alcohol moieties in 9 behave as two independent bidentate ligands in the catalytic system. The results obtained using ligand 15 having one N-sulfonylated beta-amino alcohol blocked support the argument of two independent active bidentate moieties in 9.
Hsieh
Sheng-Hsiang
SH
Department of Chemistry, National Chung-Hsing University, Taichung 402, Taiwan.
Gau
Han-Mou
HM