反应详情

To a solution of 50 g of compound 20a (MW=406.8; 1.0 eq.; prepared as described in example 2) in 500 mL of dry THF was slowly added 190 mL of (−)-DIP-Cl solution (MW=320.76; 2.75 eq. 63% in heptane) at −30° C. After stirring for 6 h 180 mL of methanol were added and the mixture was warmed to room temperature. After removal of the solvent under reduced pressure, the residue was dissolved in methanol/water (10/1) and extracted twice with heptane. After concentration of the aqueous layer, ethyl acetate was added and the resulting mixture was consecutively extracted with an aqueous NaCl solution (9%) and with an aqueous NaHCO3 solution (8.6%). The organic solvents were removed under reduced pressure and the residue was recrystallized from ethyl acetate/n-heptane (1/7) to give 41 g of the title compound after drying (40° C., 10 mbar; yield=81.2%, de(S)=89.2%).

1. customat −30° C
2. additionwere added
3. customAfter removal of the solvent under reduced pressure
4. dissolutionthe residue was dissolved in methanol/water (10/1)
5. extractionextracted twice with heptane
6. additionAfter concentration of the aqueous layer, ethyl acetate was added
7. extractionthe resulting mixture was consecutively extracted with an aqueous NaCl solution (9%) and with an aqueous NaHCO3 solution (8.6%)
8. customThe organic solvents were removed under reduced pressure
9. customthe residue was recrystallized from ethyl acetate/n-heptane (1/7)