New Applications of Camphor-Derived P,N-Ligands for Asymmetric Pd- and Ir-Catalyzed Reactions

Abstract

Ir-catalyzed asymmetric hydroboration of bicyclic hydrazine 4 in the presence of chiral ligand 1a, leads to bicyclic alcohol 5 after oxidative workup in good yield (76%) and moderate enantioselectivity (71% ee).

meso-bicyclic hydrazine - Ir-catalyzed hydroboration - t-BuOK-catalyzed addition - P,N-ligands - asymmetric catalysis

References

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[Ir(COD)Cl]₂ (3.4 mg, 5 mol, 1 mol%), ligand 1a (4.2 mg, 11 mol, 2.1 mol%) and 4 (182 mg, 0.5 mmol) were placed under Ar in a flame-dried Schlenk tube. THF (0.85 mL) was degassed at -50 °C and added to the mixture at this temperature. The reaction was stirred at r.t. for 30 min and cooled to 0 °C. Catecholborane (0.11 mL, 1 mmol) was added at 0 °C and stirred for 4 h. EtOH (0.5 mL), 3 M NaOH (0.85 mL) and 30% H₂O₂ (0.5 mL) were added and stirred at 25 °C for 16 h. The reaction mixture was extracted with EtOAc (3 × 10 mL). The organic phase was washed with 1 M NaOH (5 × 10 mL), brine, dried over MgSO₄ and concentrated in vacuo. The crude product was purified by flash chromatography (50% EtOAc in cyclohexane), affording (1S,4R,5R)-5 (145 mg, 76%, 71% ee) as a colorless liquid. The ee value was determined by HPLC [Chiralcel AD, n-hexane-i-PrOH, 80:20, 0.8 mL/min, 220 nm): t_r (min) = 14.6 (1S,4R,5R), 16.4 (1R, 4S,5S)].