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Open AccessArticle

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

1
Department of Organic Chemistry & Technology, Budapest University of Technology & Economics, Szent Gellért tér 4, H-1111 Budapest, Hungary
2
Department of Inorganic & Analytical Chemistry, Budapest University of Technology & Economics, Szent Gellért tér 4, H-1111 Budapest, Hungary
3
Department of Pharmacognosy, Semmelweis University, Üllői út 26, H-1085 Budapest, Hungary
4
Spectroscopic Research Department, Gedeon Richter Plc., Gyömrői út 19-21, H-1103 Budapest, Hungary
*
Authors to whom correspondence should be addressed.
Academic Editor: Yannick Vallée
Symmetry 2021, 13(3), 521; https://doi.org/10.3390/sym13030521
Received: 28 February 2021 / Revised: 16 March 2021 / Accepted: 18 March 2021 / Published: 23 March 2021
(This article belongs to the Collection Feature Papers in Chemistry)
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. View Full-Text
Keywords: cinchona; organocatalysis; C3-symmetry; size-enlargement; nanofiltration; asymmetric reaction cinchona; organocatalysis; C3-symmetry; size-enlargement; nanofiltration; asymmetric reaction
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MDPI and ACS Style

Kisszékelyi, P.; Fehér, Z.; Nagy, S.; Bagi, P.; Kozma, P.; Garádi, Z.; Dékány, M.; Huszthy, P.; Mátravölgyi, B.; Kupai, J. Synthesis of C3-Symmetric Cinchona-Based Organocatalysts and Their Applications in Asymmetric Michael and Friedel–Crafts Reactions. Symmetry 2021, 13, 521. https://doi.org/10.3390/sym13030521

AMA Style

Kisszékelyi P, Fehér Z, Nagy S, Bagi P, Kozma P, Garádi Z, Dékány M, Huszthy P, Mátravölgyi B, Kupai J. Synthesis of C3-Symmetric Cinchona-Based Organocatalysts and Their Applications in Asymmetric Michael and Friedel–Crafts Reactions. Symmetry. 2021; 13(3):521. https://doi.org/10.3390/sym13030521

Chicago/Turabian Style

Kisszékelyi, Péter; Fehér, Zsuzsanna; Nagy, Sándor; Bagi, Péter; Kozma, Petra; Garádi, Zsófia; Dékány, Miklós; Huszthy, Péter; Mátravölgyi, Béla; Kupai, József. 2021. "Synthesis of C3-Symmetric Cinchona-Based Organocatalysts and Their Applications in Asymmetric Michael and Friedel–Crafts Reactions" Symmetry 13, no. 3: 521. https://doi.org/10.3390/sym13030521

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