Enantioselective addition of diethylzinc to aldehydes catalyzed by titanium(IV) complexes of n ‐sulfonylated β‐amino alcohols with four stereogenic centers

An N ‐sulfonylated β‐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 β‐amino alcohols suggests that the two N ‐sulfonylated β‐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 β‐amino alcohol blocked support the argument of two independent active bidentate moieties in 9 . Chirality, 2006. © 2006 Wiley‐Liss, Inc.