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.