Primary Amine-Functionalized\nChiral Covalent Organic\nFramework Enables High-Efficiency Asymmetric Catalysis in Water

Aqueous asymmetric catalysis using chiral covalent organic\nframeworks\n(COFs) represents a significant advancement but remains to be explored.\nHerein, we present the first example of aqueous asymmetric catalysis\ncatalyzed by a primary amine-tagged chiral <i>D</i>-ADP-TAPB\nCOF. The <i>D</i>-ADP-TAPB COF was synthesized by the postsynthetic\ndeprotection of <i>D</i>-ADP-TAPB-Boc bearing a protective\ntert-butoxycarbonyl (Boc) group, which was constructed by a Schiff-base\nreaction between an alanine-derived chiral building block (<i>D</i>-ADP-Boc) and 1,3,5-tris(4-aminophenyl)benzene (TAPB).\nThe crystalline <i>D</i>-ADP-TAPB COF exhibits a uniform,\nspherical morphology with abundant, well-distributed chiral primary\namines, rendering it highly active in the asymmetric aldol reaction\nbetween cyclohexanone and 4-nitrobenzaldehyde. Notably, this reaction\nis conducted entirely in water, achieving impressive yields and enantiomeric\nexcess (ee) values of up to 90 and 85%, respectively. To the best\nof our knowledge, <i>D</i>-ADP-TAPB COF represents the first\nchiral COF catalyst with high reactivity and enantioselectivity for\nan asymmetric aldol reaction solely in water, eliminating the need\nfor conventional organic solvents. Moreover, a plausible mechanism\nfor <i>D</i>-ADP-TAPB COF-mediated aqueous asymmetric aldol\nreactions is elucidated. This work not only expands the toolbox for\ndesigning rare primary amine-functionalized chiral COFs for asymmetric\ncatalysis but also opens exciting avenues for developing green and\nwater-based enantioselective catalysis.