The confined space inside the hexameric pyrogallol[4]arene capsule (CP6) can be exploited for the catalysis of the 1,3-dipolar cycloaddition (1,3-DC) between nitrone 3 and crotonaldehyde 4, in the presence of the non-competitive benzene solvent. Differently, when the capsule CP6 is self-assembled in the commonly used chloroform solvent, its nano-cavity becomes catalytically incompetent. Diffusion NMR studies and product analysis show that in the presence of chloroform, which is stably encapsulated inside the pyrogallol[4]arene capsule, the reaction between the proline-based iminium derivative I and nitrone 3 does not occur inside the cavity but on the exterior of the CP6 capsule. Differently, in the presence of a non-competitive solvent such as benzene, the 1,3-DC occurs inside the cavity of the pyrogallol[4]arene capsule. The confinement of iminium I and nitrone 3 inside the confined space of CP6 leads to a strict control over the stereochemistry of the 1,3-DC. Thus, while the endo-stereoisomer of the isoxazolidine product 5 is favored inside the capsule, the exo-one is preferentially formed on the exterior of the capsule or in the bulk solvent. QM calculations have been performed to rationalize these stereochemical results.

Supramolecular catalysis in confined space: making the pyrogallol[4]arene capsule catalytically active in non-competitive solvent

Gaeta C.;Rescifina A.
;
2022

Abstract

The confined space inside the hexameric pyrogallol[4]arene capsule (CP6) can be exploited for the catalysis of the 1,3-dipolar cycloaddition (1,3-DC) between nitrone 3 and crotonaldehyde 4, in the presence of the non-competitive benzene solvent. Differently, when the capsule CP6 is self-assembled in the commonly used chloroform solvent, its nano-cavity becomes catalytically incompetent. Diffusion NMR studies and product analysis show that in the presence of chloroform, which is stably encapsulated inside the pyrogallol[4]arene capsule, the reaction between the proline-based iminium derivative I and nitrone 3 does not occur inside the cavity but on the exterior of the CP6 capsule. Differently, in the presence of a non-competitive solvent such as benzene, the 1,3-DC occurs inside the cavity of the pyrogallol[4]arene capsule. The confinement of iminium I and nitrone 3 inside the confined space of CP6 leads to a strict control over the stereochemistry of the 1,3-DC. Thus, while the endo-stereoisomer of the isoxazolidine product 5 is favored inside the capsule, the exo-one is preferentially formed on the exterior of the capsule or in the bulk solvent. QM calculations have been performed to rationalize these stereochemical results.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11769/537948
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