Studies on asymmetric synthesis catalyzed by S-indoline-2-carboxylic acid and S-proline derivatives

Abstract

Asymmetric reduction of ketimine is very useful for the preparation of functionalized amine compounds. Asymmetric hydrosilylation of imines with $Cl_2SiH$ has been achieved using new chiral lewis base catalsts prepared from S-indoline-2-carboxylic acid to give moderated chemical yield and enantiomeric excess. The chiral ligands containing proline moiety was synthesized from (S)-proline carboxylic acids. These chiral ligands have been examined in the catalytic asymmetric cyanation of aldehydes to give the corresponding cyanohydrins. Treatment of benzaldehydes with $Ti(iOPr)_4$ in the presence of catalytic amount of chiral ligands gave cyanohydrins with good yields and enantiomeric excess (up to 90%) with R or S-configuration depending of the configuration of chiral catalysts. When the reaction were carried out at -20℃ in $CH_2Cl_2$ with 10mol% of chiral catalyst, good chemical yields and enantioselectivity were obtained.