Synthesis Of Supported Chiral Catalysts With Varied Linkers And Their Catalytic Properties For Asymmetric Aldol Reaction

Asymmetric play a crucial role in the field of medicine pesticide and functional materials, the application of chiral catalyst is one of the effective means asymmetric reactions. L-proline cheap mild reaction conditions and effectively catalytic a variety of asymmetric reactions, is recognized as the most effective organic small molecular catalysts, but there exists some challenge, such as high dosage, limited substrate and difficulty to recycle. Recently, Supported chiral catalysts received more attention because they can not only keep the activity of small molecule effective unit, but also their special structure can help to forming reaction micro-environment and keeping high catalytic activity. Moreover supported catalysts can be recycled easily after completing reaction through simple filtration, washing and drying process in turn. In this paper, L-proline was loaded on the Merrifield resin using different length and containing special groups linkers. Then, the effect of linkers on catalytic performance for asymmetric Aldol reaction was discussed and the reaction condition was optimized.1. A series of Merrifield resin supported L-proline catalysts were synthesized using different straight chain aliphatic diamines as linkers and several chiral loaded catalysts were obtained. Their structures were characterized through the Fourier transform infrared spectroscopy and elemental analysis.The catalytic performances of the as-preparated catalysts for asymmetric Aldol reaction between cyclohexanone and p-nitrobenzene in the presence of water were discussed. The optial catalyst was screened out through contrasting the effects of linkers length on their catalytic properties. The impact factors, such as different solvent, the dosage of catalysts, and the dosage of substrates, on catalyticproformance were studied in system. Furthermore, the applicability of the substrate and reusability performance was investigated, respectively. Results exhibit that the shortest carbon chain, namely ethylenediamine as linker, Merrifield resin loaded L-proline possess high catalytic activity. Only requiring1 mol% of which in presence of traces of water, the asymmetric Aldol reaction between p-nitrobenzaldehyde and cyclohexanone can get good enantioselectivity of 93% ee, medium diastereoselectivity of 20:80 and medium yields of 51%. This catalyst possesses wide substrate applicability for asymmetry Aldol reaction, for example, cyclohexanone reacts with a variety of aromatic aldehydeasymmetric. Moreover, after being recycled for 4 times, the catalyst still keeps a certain stereoselectivity.2. A series of loaded type chiral catalyst were prepared using several aromatic diamines as the linker and their structures were characterized by Fourier transform infrared spectroscopy and elemental analysis. The as-preparated catalysts were applied to catalysis asymmetric Aldol reaction between cyclohexanone and p-nitrobenzaldehyde in the water phase and organic phase solvent. The optial catalyst was screened out through contrasting the effects of linker length on their catalytic properties. The impact factors, such as the dosage of catalyst and solvent on catalytic proformance were studied in system.Furthermore, the applicability of the substrate and reusability performance was investigated, respectively.Results exhibit that in the as-preparated with only benzene ring of aromatic diamine applied to asymmetric Aldol reaction in water, namely p-phenylenediamine as linker, Merrifield resin loaded L-proline possess better catalytic activity. Choose contain sulfone and sulfonamide based aromatic amine as a linker, its catalytic performance and stereoselectivity improved. The catalyst whose linker is 4,4’-Diaminobenzene–sulphanilide exhibited the best catalytic performance. Only requiring 1 mol% of which in 200 μL water,the asymmetric Aldol reaction between p-nitrobenzaldehyde and cyclohexanone can get high enantioselectivity of 98% ee, medium diastereoselectivity of 18:82 and medium yields of 62%. This catalyst possesses good reusability performance, after being recycled for 4 times, its catalytic activity was not significantly reduced.The results exhibited water is the best solvent for the Aldol asymmetric reaction catalyzed by as-preparated catalysts. Moreover, whether different carbon chain length of aliphatic or only benzene ring of aromatic diamine as the linker, both the catalysts with the short linker showed good catalytic activity. Of which the catalyst with the aromatic amine containing sulfonamide group as the linker showed higher catalytic activity. It is presumed that sulfonamide group strengthen the hydrogen bonding interaction, this is beneficial to stabilizing the transition state, which brought about its catalytic higher activity and stereoselectivity.