CATALYTIC ENANTIOSELECTIVE REACTIONS USIN G C-2-SYMMETRICAL DISULFONAMIDES AS CHIRAL LIGANDS

In order to realize an efficient enantioselective reaction through a c atalytic process, we were interested in modifying a Lewis acid by elec tron-withdrawing chiral ligands. In such a modified Lewis acid, the ch iral ligand will not only provide a chiral environment, but also incre ase the acidity of Lewis acid. among various electron-withdrawing grou ps we selected C-2-symmetric disulfonamide as a chiral ligand consider ing both electronic and steric characters. We developed (1) alkylation of aldehydes catalyzed by disuifonamide-Ti(O-i-Pr)(4)-dialkyIzinc sys tem, 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 ch iral ligand will be helpful in developing other type of catalytic and enantioselective reactions.