1997 年 55 巻 8 号 p. 714-724
In order to realize an efficient enantioselective reaction through a catalytic process, we were interested in modifying a Lewis acid by electron-withdrawing chiral ligands. In such a modified Lewis acid, the chiral ligand will not only provide a chiral environment, but also increase the acidity of Lewis acid. Among various electron-withdrawing groups we selected C2-symmetric disulfonamide as a chiral ligand considering both electronic and steric characters. We developed (1) alkylation of aldehydes catalyzed by disulfonamide-Ti (O-i-Pr) 4-dialkylzinc system, and (2) the first Simmons-Smith type cyclopropanation of allylic alcohols by Et2Zn-CH2I2-disulfonamide or Et2Zn-CH2I2-disulfonamide-Al system. The concept of modifying Lewis acid by electron-withdrawing chiral ligand will be helpful in developing other type of catalytic and enantioselective reactions.