Functionalized ionic liquids catalyzed direct aldol reactions

A series of functionalized ionic liquids (FILs) incorporated with chiral-pyrrolidine unit have been synthesized and tested as reusable organocatalysts for direct aldol reactions. FIL 1b in combination with acetic acid and water as additives could effectively catalyze direct aldol reactions of various ketone donors in high yields and the FIL catalyst was easily recycled and reused for six times with slight reduction in activity. Based on experimental observations as well as previous reports, we proposed that the reactions occurred via syn-enamine intermediate and the ionic-liquid moiety in the FIL provides some space shielding for the participating aldehyde acceptors that accounts for the modest enantioselectivities observed in the reactions. (c) 2007 Elsevier Ltd. All rights reserved.