Asymmetric Anion-π Catalysis: Enamine Addition to Nitroolefins on π-Acidic Surfaces

Abstract

Here we provide experimental evidence for anion-π catalysis of enamine chemistry and for asymmetric anion-π catalysis. A proline for enamine formation on one side and a glutamic acid for nitronate protonation on the other side are placed to make the enamine addition to nitroolefins occur on the aromatic surface of π-acidic naphthalenediimides. With increasing π acidity of the formally trifunctional catalysts, rate and enantioselectivity of the reaction increase. Mismatched and more flexible controls reveal that the importance of rigidified, precisely sculpted architectures increases with increasing π acidity as well. The absolute configuration of stereogenic sulfoxide acceptors at the edge of the π-acidic surface has a profound influence on asymmetric anion-π catalysis and, if perfectly matched, affords the highest enantio- and diastereoselectivity.

Interfacing Functional Systems

“…1). Independent of size and nature, primary components can be small molecules (catalysts, [2,3] transporters, [3,4] chromophores, [5] vitamins, [6] bioadhesives [7] ), macromolecules (enzymes, proteins, [6,8] polymers [5,9] ), supramolecules (protein oligomers, [6,8] polymersomes, [9] liposomes [3] ), cells, [4,8] devices, [5,7] and so on. Interfacing of primary componentsnon-covalent, dynamic-covalent or covalent -produces primary systems.…”

“…The function of interest of this primary component is the binding of holes (oxidation), cations, cationic reactive intermediates or cationic transition states on π-basic surfaces and the binding of electrons (reduction), anions, anionic reactive intermediates or anionic transition states on π-acidic surfaces. [2] Whereas cation-π interactions in all different forms are very well documented, anion-π and ionpair-π interactions are of current interest because they are almost unexplored in functional systems. [2,10] For several good reasons, naphthalenediimides (NDIs) such as 1 offer the π-acidic surface of choice for a promising primary component (Fig.…”

“…[2] Whereas cation-π interactions in all different forms are very well documented, anion-π and ionpair-π interactions are of current interest because they are almost unexplored in functional systems. [2,10] For several good reasons, naphthalenediimides (NDIs) such as 1 offer the π-acidic surface of choice for a promising primary component (Fig. 2).…”

“…[11] Covalent interfacing of primary system 2 with a proline base, another functional component, through an extended turn affords a covalently coupled, formally secondary system 3. [2] The emergent property is the catalysis of enamine addition to nitroolefins, a much more important reaction than the Kemp elimination catalyzed by the primary system. Interfacing with chiral sulfoxides at the edge of the π-acidic surface yields the formally tertiary covalent coupled system 4.…”

“…Interfacing with chiral sulfoxides at the edge of the π-acidic surface yields the formally tertiary covalent coupled system 4. [2] The emergent property is stereoselectivity, i.e. asymmetric are placed in the oligothiophene channel to drive holes away from the solid surface, whereas fullerenes with three, two and one cyclopropane are interfaced to drive electrons toward the solid surface.…”