Solvent-free asymmetric direct aldol reactions organocatalysed by recoverable (Sa)-binam-L-prolinamide

The combination of (Sa)-binam-L-Pro (5 mol %) and benzoic acid (10 mol %) was used as catalysts in the direct aldol reaction between diff. erent aliphatic ketones and 4-nitrobenzaldehyde under solvent-free reaction conditions. Three diff. erent procedures are assayed: magnetic stirring (method A), magnetic stirring after previous dissolution in THF and evaporation (method B), and ball mill technique (method C), methods A and B being the simplest. These reaction conditions allowed us to reduce the amount of required ketone to 2 equiv to give the aldol product in similar reaction times and regio-, diastero-, and enantioselectivities than in organic or aqueous solvents. (c) 2007 Elsevier Ltd. All rights reserved.