New Organocatalytic Strategies for the Selective Synthesis of Centrally and Axially Chiral Molecules

Di Iorio, Nicola (2017) New Organocatalytic Strategies for the Selective Synthesis of Centrally and Axially Chiral Molecules, [Dissertation thesis], Alma Mater Studiorum Università di Bologna. Dottorato di ricerca in Chimica, 29 Ciclo.
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In this thesis are presented many examples of asymmetric organocatalyzed reactions. First, we discuss the vinylogous reactivity of non-symmetric 3-alkylideneoxindoles. Chiral substrates of this kind are privileged in the biological and pharmaceutical areas which is why it is important to have efficient methodologies to synthesize them, but due to their peculiar structure many possible stereochemical outcomes are available in this reaction. Therefore, the aim of this work is to simultaneously control the regio- diastereo- and enantioselectivity of the reaction of these substrates with nitroolefines and we did so using a thiourea-derived cinchona alkaloid as a bifunctional catalyst. Then we proved the reaction generality and we also gained a significant insight on the reaction mechanism performing appropriate experiments that allowed us to account for the almost complete selectivity observed. Next, we switch to axial chirality and present the desymmetrization of hindered N-aryl maleimides to generate atropisomeric succinimides. We envisioned that the crucial point of this strategy was to selectively direct the nucleophile towards only one of the electrophilic prochiral carbons of the maleimide in order to simultaneously form a stereocenter and reveal the distant chiral axis. To do so we employed different nucleophilic substrates in combination with different organocatalytic activation modes and we could demonstrate the effectiveness of this methodology obtaining the atropisomeric products in overall high yields and selectivity. The last part concerns the organocatalitic Friedel-Crafts reaction of hindered 2-naphthols with 4-substituted indenones affording an atropisomeric compound with an unconventional C(sp2)-C(sp3) chiral axis. In this reaction, the newly formed bond is itself the chiral axis and this is the very first example of such a thing realized diastereo- and enantioselectively. In summary, we show how iminium ion catalysis, promoted by cinchona alkaloid-derived primary amine, is an excellent way to perform this reaction obtaining products with complete diastereoselectivity and high enantioselectivity

Tipologia del documento
Tesi di dottorato
Di Iorio, Nicola
Dottorato di ricerca
Settore disciplinare
Settore concorsuale
Parole chiave
Organocatalysis, vinylogy, desymmetrization, atropisomers, axial chirality
Data di discussione
19 Aprile 2017

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