Systematic Parameter Determination Aimed at a Catalyst-Controlled Asymmetric Rh(I)-Catalyzed Pauson-Khand Reaction

Area of Science:

• Organic Chemistry
• Catalysis
• Asymmetric Synthesis

Background:

• Transition metal catalysis enables complex cyclic compound synthesis.
• The asymmetric Pauson-Khand reaction (PKR) is valuable but faces challenges with substrate scope and selectivity.
• Understanding factors influencing PKR is crucial for optimizing chiral synthesis.

Purpose of the Study:

• To identify predictive parameters for yield and enantioselectivity in catalyst-controlled asymmetric PKR.
• To explore the influence of ligand properties, solvent, and substrate structure on reaction outcomes.
• To enable the synthesis of ring-fused cyclopentenones with chiral quaternary carbon centers.

Main Methods:

• Utilized 1,6-enynes with 2,2-disubstituted alkenes in Rh(I)-catalyzed PKR.
• Correlated bisphosphine ligand parameters (e.g., Pd lone pair orbital energy, P-aryl angle) with enantioselectivity.
• Investigated solvent properties (dipole moment, hydrogen bond basicity) and steric effects (Sterimol B1 values) on reaction outcomes.

Main Results:

• Established strong correlations between ligand parameters and enantioselectivity (R² = 0.99, 0.91).
• Demonstrated solvent effects on enantioselectivity based on precursor polarity (R² = 0.94, 0.93).
• Showed significant impact of counterions and alkyne substituent steric demand (R² = 0.99).
• Found computed C≡C wavenumber directly correlates with asymmetric PKR yield.

Conclusions:

• Key parameters governing asymmetric PKR yield and enantioselectivity have been identified.
• Ligand electronics, solvent polarity, and steric factors are critical for controlling chiral quaternary center formation.
• This study provides a predictive framework for optimizing asymmetric PKR for complex molecule synthesis.