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
La Manna P.;Talotta C.;Gaeta C.;Della Sala P.;De Rosa M.;Soriente A.;Neri P.
2022-01-01
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
