Immobilized Catalysts Derived From (1R,2R) -1,2-Diaminocyclohexane And Their Application In Asymmetric Aldol Reactions

In this paper, a primary-tertiary amine organocatalyst had been synthesized by using (1R,2R)-1,2-cyclohexanediamine as a chiral material through protection of amine, nucleophilic substitution and deprotection. Then the primary-tertiary amine organocatalyst could be immobilized by one-pot method into various supports such as silica, zinc ferrite and iron oxide to obtain supported organocatalyst derived from (1R, 2R)-1,2-cyclohexanediamine.The composition, structure and morphology of immobilized organocatalysts were characterized by IR, TG, N2 adsorption and desorption isotherms, XRD, SEM, TEM,VSM. It was shown that the nano-sized Fe3O4@DACH-VMBz accumulated into a loose and porous material, which possessed the non-uniform microporous and mesoporous structure.In the asymmetric Aldol reaction of nitrobenzaldehyde and cyclohexanone, Fe3O4-supported Fe3O4@DACH-VMBz organocatalyst had the superior catalytic per-formances to SiO2@DACH-VMBz and ZnFe2O4@DACH-VMBz. Using 4-nitro-benzaldehyde (0.1 mmol) as a example, the influential factors such as the immobi-lized mount of orgaoncatalyst, solvent, temperature, used amount of organocatalyst, water, acid and cyclohexanone on catalytic performances were investigated in detail. The optimal reaction conditions was that Fe3O4@DACH-VMBz (100 mg,0.0186 mmol DACH), CH3CN (2 mL), H2O (2 mmol), TFA (0.03 mmol), cyclohexanone (1 mmol),10 ℃. Under these optimal conditions, various o, m and p-substituted ben-zaldehydes gave excellent to moderate catalytic performances (30-99% yields,66.2-98.1%ee and anti/syn= 98-80/2-20). Among them,2-chlorobenzaldehyde afforded the best catalytic performances:>99% yield,98.1% ee and anti/syn= 98/2. After the com-pletion of reaction, the supported organocatalyst could be easily recovered by using external magnet. In the cycled experiments for seven reused times, the catalytic per-formances gradually declined.