Prolinamide and Prolinamide Tagged with Ionic Liquid Intercalated in Bentonite Clay, a Recyclable Catalyst for Asymmetric Aldol Reactions

Abstract

AbstractThe imidazolium‐based chiral ionic liquids containing prolinamide moiety and prolinamide were intercalated in bentonite clay and evaluated in asymmetric aldol reactions of aromatic aldehydes or isatins with acetone or cyclohexanone. The 10 mol% of chiral ionic liquid having S‐phenylethylamine moiety 2 a catalyzed the direct enantioselective aldol reaction of isatins and acetone in i‐PrOH at −20 °C and afforded the corresponding 3‐alkyl‐3‐hydroxy indolin‐2‐ones in 72–98 % yields and 37–80 % ee's. The prolinamide intercalated in bentonite clay (0.125 g, 10 mol%) gave corresponding aldol products in 32–82 % yields and 38–91 % ee's. However, prolinamide intercalated bentonite clay was found to be less active as compared to chiral ionic liquids containing prolinamide. The prolinamide intercalated bentonite clay 8 was reused in four catalytic cycles, with a slight loss of activity and selectivity of the catalyst after the third recycling.