Fig. 4. Demonstration of diastereodivergence.

Reaction conditions: Cu(CH₃CN)₄PF₆ (5 mol%) and pyridine bis(oxazoline) ligand ent-L3 (10 mol%) were stirred in THF (0.5 mL) at 25 °C for 1 h, then NHC precatalyst 4a (5 mol%), 1 (0.15 mmol), 2 (0.1 mmol), MeOH (0.5 mmol), Na₂CO₃ (0.1 mmol) and THF (0.5 mL) were added to the reaction mixture and stirred for 12 h under N₂. Diastereomeric ratio (d.r.) was determined by ¹H NMR spectroscopic analysis. Isolated yields. The enantiomeric excess (e.e.) was determined by HPLC. ^aCu(CH₃CN)₄PF₆ (7.5 mol%), 2,6-bis((4 R,5 S)-4,5-diphenyl-4,5-dihydrooxazol-2-yl)pyridine L5 (15 mol%), NHC precatalyst 4a (7.5 mol%), 1 (0.15 mmol), styryl-substituted propargylic benzoates 2 (0.1 mmol), Na₂CO₃ (0.2 mmol), and DCM (1.0 mL) were used, at 15 °C.