An Improved Protocol for the Direct Asymmetric Aldol Reaction in Ionic Liquids, Catalysed by Onium Ion‐Tagged Prolines

Abstract

Abstract Two onium ion‐tagged prolines, imidazolium bis(trifluoromethylsulfonyl)imide‐substituted proline 6 and butyldimethylammonium bis(trifluoromethylsulfonyl)imide‐substituted proline 7 , were synthesised and their catalytic activity in the direct asymmetric aldol condensation was studied in ionic liquids. For the reaction of acetone with various aldehydes, using 5 % of the catalyst, the yields of the aldols varied between 50–85 % while the ee values were in the 80–85 % range. Other ketones were studied too, the yields obtained in those cases being in the 35–78 % range while the enantioselectivities varied between 75–94 %.