Asymmetric reduction of ketones catalyzed by α,α-diphenyl-(L)-prolinol modified with imidazolium ionic liquid and BH3·SMe2 as a recoverable catalyst

Abstract The synthesis of α,α-diphenyl-4- trans -hydroxy-(L)-prolinol modified with imidazolium based ionic liquids was carried out with trans -α,α-diphenyl-4-hydroxy-(L)-prolinol, 5-bromovaleric acid or 1,5-dibromopentane and imidazole. α,α-Diphenyl-4-hydroxy-(L)-prolinol modified with imidazolium ionic liquid was treated with BH 3 ·SMe 2 which generate 1,3,2-oxazaborolidine, that acts as a catalyst for asymmetric reduction of prochiral ketones. α,α-Diphenyl-4-hydroxy-(L)-prolinol modified with imidazolium ionic liquids (PF 6 anion) with BH 3 ·SMe 2 found to be an efficient catalyst (10 mol%) for the reduction of the acetophenone, gave 99% yield and 87–84% ee. The catalytic method has wide applicability for a variety of substrates. 1,3,2-oxazaborolidine containing ether linkage ionic liquid was recovered and reused up to 4 cycles with 99–91% yields and 87–81% ee’s.