Supported L-proline on zirconium phosphates methyl and/or phenyl phosphonates as heterogeneous organocatalysts for direct asymmetric aldol addition

Zirconium phosphates methyl and/or phenyl phosphonates-supported L-proline have been prepared as amorphous solids by precipitation of (4R)-4-(phosphonooxy)-L-proline, methyl and/or phenyl phosphonic acid with ZrOCl2. The supported L-proline catalysts were tested on the direct asymmetric aldol addition of cyclohexanone to p-nitrobenzaldehyde in DMF/H2O (9:1) and in sole water. The hydrophobic groups on solid surface favor reagents' diffusion toward proline chiral moiety increasing the catalytic activity of supported L-proline. High diastereoselectivity (anti/syn up to 94:6) and high enantiomeric excess up to 97% have been obtained. (C) 2011 Elsevier Inc. All rights reserved.