Rh(I) 手性雙環雙烯催化不對稱合環反應之系統性效應研究:分子對稱性×配基幾何 Systematic Investigation of Rh(I)-Catalyzed Asymmetric Cycloaddition Reactions with Chiral Bicyclic Diene Ligands: Interplay Between Molecular Symmetry and Ligand Geometry
Asymmetric cyclization catalyzed by rhodium complexes is a valuable route to chiral cyclic molecules, which serve as key intermediates in pharmaceutical synthesis. However, achieving high selectivity and sustainability in these reactions requires careful ligand design. This project addresses that challenge by investigating the influence of molecular symmetry on ligand design on the outcome of Rh(I)-catalyzed asymmetric cyclization.
In a novel student-led study, a series of chiral ligands was designed and synthesized, featuring variations in symmetry and steric properties. The goal was to identify an optimal ligand structure that maximizes enantioselectivity and regioselectivity while maintaining high catalytic efficiency. A systematic screening was conducted using these ligands in a model Rh-catalyzed asymmetric cyclization reaction. Reaction progress and outcomes were monitored using proton NMR spectroscopy to confirm product formation and chiral HPLC analysis to quantify enantiomeric excess. Each experiment was performed under optimized conditions consistent with green chemistry principles (e.g., catalytic quantities of Rh and minimal solvent waste).
Key findings highlight the profound impact of ligand symmetry on catalytic performance. One student-designed ligand with a C2-symmetric framework emerged as the top performer, delivering an enantiomeric excess above 97% (ee) and a regioselectivity ratio exceeding 20:1 (major:minor) in the cyclization reaction. This ligand also afforded excellent yield and robust catalytic stability. The high level of stereocontrol achieved demonstrates that tailored ligand architecture can precisely steer the reaction pathway.
These results are significant both academically and practically. They provide new insights into structure selectivity relationships in asymmetric catalysis and confirm that incorporating molecular symmetry in ligand design can drastically enhance selectivity. For pharmaceutical chemistry, the ability to efficiently produce enantiopure cyclic compounds is invaluable, potentially streamlining drug synthesis. Additionally, the improved catalytic efficiency and selectivity contribute to greener chemistry by reducing waste and avoiding extensive purification, aligning the project with broader sustainable synthesis goals.