Efficient homogeneous-like enantioselective catalysis of bulky chiral catalyst: Covalent immobilization of chiral spirocyclic phosphoric acid to polystyrene brushes grafted on SiO2 nanospheres

Abstract

To solve mass transfer limitation and multi-step immobilization of bulky chiral phosphoric acids in heterogeneous asymmetric catalysis, this paper develops a direct immobilization of (R)-6,6'-di(9-anthryl)spirobiindane phosphoric acid ((R)-AnSPA) via Friedel-Crafts alkylation onto SiO2-grafted poly(p-vinylbenzyl chloride) (PVBC) brushes (PVBC@SiO2) and hollow mesoporous PVBC nanospheres (HMPNs), affording supported organocatalysts (AnSPA#PVBC@SiO2 and AnSPA@HMPNs), respectively. Owing to the good dispersibility of PVBC brushes in organic solvents, the PVBC brush-anchored (R)-AnSPA with an open-ended structure enables the enantioselective desymmetrization of oxetanes with mercaptobenzothiazoles to perform in a homogeneous-like manner, leading to the improved mass transfer of reactants due to alleviative steric hindrance. Compared to homogeneous (R)-AnSPA, the PVBC brush-anchored (R)-AnSPA shows the decrements in yield and enantioselectivity below 2%. However, the HMPNs-anchored (R)-AnSPA shows the larger decrements in yields (3‒6%) and enantioselectivities (3‒7% ee). Furthermore, AnSPA#PVBC@SiO2 has a good reusability for in enantioselective desymmetrization with no significant decreases in yield and enantioselectivity. Particularly, the deactivated AnSPA#PVBC@SiO2, caused by the hydrolysis of phosphate ester in (R)-AnSPA, can be easily renovated to its fresh state by dealing with POCl3. Overall, the direct immobilization of (R)- AnSPA to PVBC brushes and renovation of deactivated (R)-AnSPA provide an effective strategy for achieving a high sustainability of expensive chiral spirocyclic phosphoric acids in large-scale synthesis.

Supplementary files

Article information

Article type
Paper
Submitted
18 Apr 2025
Accepted
05 Jun 2025
First published
06 Jun 2025

Org. Biomol. Chem., 2025, Accepted Manuscript

Efficient homogeneous-like enantioselective catalysis of bulky chiral catalyst: Covalent immobilization of chiral spirocyclic phosphoric acid to polystyrene brushes grafted on SiO2 nanospheres

Y. Luo, W. Tian, Y. Zhou, C. He and X. Ma, Org. Biomol. Chem., 2025, Accepted Manuscript , DOI: 10.1039/D5OB00641D

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