Preparation Of Chiral Amine-Based Catalysts And Their Applications In Asymmetric Synthesis

Oxime benzene and furan derivatives are important intermediates in the synthesis of cefuroxime. Some literature has reported that a type of homogeneous catalysts possesses some excellent catalytic properties in the asymmetric syntheses of nitro-olefins and 1,3-cyclohexanedione to oxime benzene and furan derivatives. However, this type of homogeneous catalysts is rather expensive and often difficultly separated from the reaction media, leading to some difficulty in recyclable use. The current research, therefore, aims to develop a synthesis method to prepare chiral heterogeneous catalysts that can be used in the asymmetric syntheses of nitro-olefins and 1,3-cyclohexanedione to oxime benzene and furan derivatives.Because SBA-15 mesoporous material possesses a highly ordered pore structure, a large specific surface area, a controlled pore wall thickness, and a good hydrothermal stability, this mesoporous material shows some potential in the application of catalysis and adsorption-based separation. Owing to its structural stability and functionability, thioureido groups and chiral-amino groups can be separately grafted onto SBA-15 to get SBA-15 supported chiral catalysts. Then these synthesized catalysts will be applied to the asymmetric syntheses of nitro-olefins and 1,3-cyclohexanedione to oxime benzene and furan derivatives. The main research contents and results are symmarized as follows:First of all, SBA-15 with high thermal stability, large surface area, and high porosity was synthesized. Then hydroxy-phenyl-2,4-isothiocyanate was grafted onto SBA-15 via the reaction of hydroxy-phenyl-2,4-isothiocyanate with the silanols on the surface of SBA-15, the so-called NCS-SBA-15 in abbreviation. In the following step, the chiral amine (1R,2R)-cyclohexanediamine was grafted onto NCS-SBA-15, and the resultant catalyst is called SN-SBA-15. Moreover, the synthesized SBA-15, NCS-SBA-15, and SN-SBA-15 were characterized in detail. Finally, the synthesized catalyst SN-SBA-15 was applied to the asymmetric Michael addition of nitro-olefins and 1,3-cyclohexanedione to oxime benzene and furan derivatives and systematically investigated the catalytic properties of SN-SBA-15 in line with optimization of the reaction conditions. Furthermore, the catalytic properties of SN-SBA-15 in the asymmetric Michael addition with different reactants were also investigated, and the recylcability of the catalyst and the reaction scale-up were also conducted.The results indicate that SN-SBA-15 shows some good catalytic properties in asymmetric Michael addition of nitro-olefins and 1,3-cyclohexanedione to oxime benzene and furan derivatives. Under the optimized conditions, the yields of E and Z products are 39.8% and 27.9% with corresponding enantioselectivities of 42% and 62%, respectively. The chiral catalyst is recyclable but the active species can be leached to some extent during reaction.