| Abstract
| - A series of N-sulfonylated β-amino alcohols (R,S)-3, (1R,2S)-PhCH(OH)CH(NHSO2R)CH2Ph,was prepared from reaction of various alkyl- or aryl-sulfonyl chlorides with (1R,2S)-2-amino-1,3-diphenylpropanol. A 1H NMR study of these ligands shows a correlation of electron-withdrawing abilities of ligands with electronic properties of R substituents on the sulfonylgroup. The asymmetric diethylzinc additions to benzaldehyde catalyzed by titanium(IV)complexes of (R,S)-3 were carried out, and yields and enantioselectivities of the desired (R)-1-phenylpropanol increase with increasing electron-donating abilities of R substituents. Adimeric titanium(IV) complex 4 was prepared, and the structure of 4 shows an interestingfeature of inequivalent titanium metal centers with one sulfonamide of the chiral ligandbonded to a Ti metal center in a η2-fashion and another sulfonamide bonded to the secondTi metal center in a η1-fashion. The complex 4 is not an effective catalyst for the asymmetricdiethylzinc addition reaction. With further addition of Ti(O-i-Pr)4, the resulting systemsbecome effective with results nearly identical to the in situ-formed catalytic systems. Anotherinteresting feature is that the 1H spectrum of 4 shows the presence of at least four isomericspecies in CD2Cl2 at 0 °C, and possible structures of these species are discussed.
- Enantioselective additions of diethylzinc to benzaldehyde catalyzed by Ti(IV) complexes of N-sulfonylate β-amino alcohols were carried out, and the study shows that reactivities and stereocontrol are affected by R substituents of the sulfonamide group, with R of an electron-donating p-tolyl or p-methoxyphenyl giving the best stereocontrol of 96% ee. A dimeric titanium(IV) complex 4 along with excess Ti(O-i-Pr)4 is also an effective catalytic system.
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