Primary Amine-Functionalized Chiral Covalent Organic Framework Enables High-Efficiency Asymmetric Catalysis in Water
Junyi Li, Kai Zhang, Xihao Tang, Xi Yang, Hong Chen, Sheng‐Run Zheng, Jun Fan, Mubiao Xie, Wei‐Guang Zhang, Xinle Li, Song‐Liang Cai
Abstract
Aqueous asymmetric catalysis using chiral covalent organic frameworks (COFs) represents a significant advancement but remains to be explored. Herein, we present the first example of aqueous asymmetric catalysis catalyzed by a primary amine-tagged chiral D -ADP-TAPB COF. The D -ADP-TAPB COF was synthesized by the postsynthetic deprotection of D -ADP-TAPB-Boc bearing a protective tert-butoxycarbonyl (Boc) group, which was constructed by a Schiff-base reaction between an alanine-derived chiral building block ( D -ADP-Boc) and 1,3,5-tris(4-aminophenyl)benzene (TAPB). The crystalline D -ADP-TAPB COF exhibits a uniform, spherical morphology with abundant, well-distributed chiral primary amines, rendering it highly active in the asymmetric aldol reaction between cyclohexanone and 4-nitrobenzaldehyde. Notably, this reaction is conducted entirely in water, achieving impressive yields and enantiomeric excess (ee) values of up to 90 and 85%, respectively. To the best of our knowledge, D -ADP-TAPB COF represents the first chiral COF catalyst with high reactivity and enantioselectivity for an asymmetric aldol reaction solely in water, eliminating the need for conventional organic solvents. Moreover, a plausible mechanism for D -ADP-TAPB COF-mediated aqueous asymmetric aldol reactions is elucidated. This work not only expands the toolbox for designing rare primary amine-functionalized chiral COFs for asymmetric catalysis but also opens exciting avenues for developing green and water-based enantioselective catalysis.