Synthesis of C3-Symmetric Cinchona-Based Organocatalysts and Their Applications in Asymmetric Michael and Friedel–Crafts Reactions

Symmetry

Zsófia Garádi¹  Péter Kisszékelyi²  Petra Kozma²  József Kupai²  Péter Huszthy²  Béla Mátravölgyi²  Zsuzsanna Fehér²  Péter Bagi²  Sándor Nagy²  Miklós Dékány³ 

[1] Department of Inorganic & Analytical Chemistry, Budapest University of Technology & Economics, Szent Gellért tér 4, H-1111 Budapest, Hungary;Department of Organic Chemistry & Technology, Budapest University of Technology & Economics, Szent Gellért tér 4, H-1111 Budapest, Hungary;Spectroscopic Research Department, Gedeon Richter Plc., Gyömrői út 19-21, H-1103 Budapest, Hungary;

关键词: cinchona;    organocatalysis;    C₃-symmetry;    size-enlargement;    nanofiltration;    asymmetric reaction;   

DOI  :  10.3390/sym13030521

来源: DOAJ

【 摘 要 】

In this work, anchoring of cinchona derivatives to trifunctional cores (hub approach) was demonstrated to obtain size-enlarged organocatalysts. By modifying the cinchona skeleton in different positions, we prepared four C₃-symmetric size-enlarged cinchona derivatives (hub-cinchonas), which were tested as organocatalysts and their catalytic activities were compared with the parent cinchona (hydroquinine) catalyst. We showed that in the hydroxyalkylation reaction of indole, hydroquinine provides good enantioselectivities (up to 73% ee), while the four new size-enlarged derivatives resulted in significantly lower values (up to 29% ee) in this reaction. Anchoring cinchonas to trifunctional cores was found to facilitate nanofiltration-supported catalyst recovery using the PolarClean alternative solvent. The C₃-symmetric size-enlarged organocatalysts were completely rejected by all the applied membranes, whereas the separation of hydroquinine was found to be insufficient when using organic solvent nanofiltration. Furthermore, the asymmetric catalysis was successfully demonstrated in the case of the Michael reaction of 1,3-diketones and trans-β-nitrostyrene using Hub³-cinchona (up to 96% ee) as a result of the positive effect of the C₃-symmetric structure using a bulkier substrate. This equates to an increased selectivity of the catalyst in comparison to hydroquinine in the latter Michael reaction.

【 授权许可】

Unknown