Rational Design of Recyclable Helical Polymeric Catalysts Bearing Pyrrolidine Motifs for High-Efficiency Asymmetric Aldol Reactions

To address the challenges of poor recyclability and stability in small-molecule catalysts for asym­metric synthesis, this study developed a helical polymer catalyst with precisely engineered pyrrolidine catalytic centers through rational molecular design. A novel helical polymer catalyst (Poly-1200) was successfully synthesized via palladium-initiated isocyanide monomer polymerization followed by Boc-deprotection. This catalyst demonstrated outstanding stereocontrol in isopropyl alcohol without additives. Using cyclohexanone and 4-nitrobenzaldehyde as model substrates, the reaction achieved 98% enantiomeric excess (ee). Notably, substituting cyclohexanone with cyclopentanone and employing trifluoromethyl-substituted benzaldehydes (4-CF3 or 2-CF3) significantly enhanced stereoselectivity, yielding 99% ee with improved diastereomeric ratio (dr) values of 72:28 and 67:33, respectively. Importantly, the catalyst retained 94% ee and over 93% recovery rate after three cycles, overcoming the technical bottleneck of poor recyclability in conventional organocatalysts. This work provides an innovative design paradigm for developing highly efficient and recyclable polymer-based catalytic systems, merging macromolecular engineering with advanced stereochemical control.