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

Abstract

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, 13 C 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.

Recyclable Organocatalysts in Asymmetric Reactions

“…2.17 ) [58] . Moreover, for proline anchorage, two strategies were applied: grafting on preformed silica gels or synthesis via sol -gel processes.…”

Copper(I) complex of 1,3‐DimethylBarbituric acid modified SBA‐15 and its catalytic role for the synthesis of 2,3‐Dihydroquinazolin‐4(1H)‐ones and Imidazoles

“…Santa Barbara Amorphous (SBA‐15) possess a hexagonal array of uniform pores is similar to structure MCM‐41 and has also the larger pores (adjustable pore size from 3 to 30 nm), thicker pore walls and greater stability in aqueous solutions compared to MCM‐41. So SBA‐15 provide a high potential for nanomaterial chemosensors and adsorbent, catalysis and other applications . Besides, the internal surfaces of these mesoporous silica materials have a large number of hydroxyls, which reaction of these silanol groups with various alkoxysilanes has been widely used for preparing functionalized SBA‐15 by covalent grafting with various organic moieties .…”

Silica-supported l-proline organocatalysts for asymmetric aldolisation

“…[22][23][24] This method has the following main advantages: easy handling and no air-sensitive catalytic system; a facile work-up of the reaction by filtration to separate the catalyst from the products in solution and an easy recovery of the solid catalyst in addition to its possible recycling. Some authors have successfully anchored organocatalysts on organic polymers (polystyrene, 25-30 polyethyleneglycol 31-33 ); zeolithes, 34,35 mesoporous silica [34][35][36][37][38][39][40] and iron oxide nanoparticles 41 have also been used as inorganic supports by grafting methods.…”