Proline and benzylpenicillin derivatives grafted into mesoporous MCM-41: Novel organic–inorganic hybrid catalysts for direct aldol reaction

New organic–inorganic hybrid catalysts were synthesized by covalent grafting of proline and benzylpenicillin derivatives into mesoporous MCM-41. These catalysts were extensively characterized using FT-IR, 13C CP MAS solid state NMR, XRD and TEM techniques. These were used as catalysts for direct, asymmetric aldol reaction between acetone and activated aromatic aldehydes. In the reaction of 4-nitro and 4-fluoro benzaldehyde, the aldol products were obtained in 36% and 59% ee respectively. The catalysts were reusable with neither significant drop in enantioselectivity nor loss of mesostructure. An attempt was made to substantiate the proposed ‘enamine’ mechanism for direct aldol reaction by trapping the intermediate between proline-MCM-41 and acetone.