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温度

0 °C

To a solution of the crude dihydroartemisinin in chloroform (40 mL) and methanol (1 mL, 24.8 mmol) was added boron trifluoride etherate (0.16 mL, 1.24 mmol) at 0° C. The reaction was stirred at 0° C. for 15 minutes, slowly warmed up to room temperature and stirred at room temperature for 3 hours. The reaction was monitored by TLC until all starting material was consumed. The reaction mixture was quenched with water (50 mL) and diluted with chloroform (25 mL). The two phases were separated, and the aqueous layer was extracted with chloroform (30×2 mL). The combined organic layers were washed with brine, dried over magnesium sulfate, filtered and concentrated under reduced pressure to afford crude product which was further purified by column chromatography on Florisil (1%-10% EtOAc/hexanes) to give two artemisinin isomers as white solids: β-isomer (0.29 g, 0.98 mmol, 79%) mp 73°-74.5° C.; α-isomer (0.05 g, 0.17 mmol, 14%), with each having a 1H NMR spectrum identical to that reported in the literature. ##STR33##

1. temperatureslowly warmed up to room temperature
2. stirringstirred at room temperature for 3 hours
3. customwas consumed
4. customThe reaction mixture was quenched with water (50 mL)
5. additiondiluted with chloroform (25 mL)
6. customThe two phases were separated
7. extractionthe aqueous layer was extracted with chloroform (30×2 mL)
8. washThe combined organic layers were washed with brine
9. dry with materialdried over magnesium sulfate
10. filtrationfiltered
11. concentrationconcentrated under reduced pressure
12. customto afford crude product which
13. customwas further purified by column chromatography on Florisil (1%-10% EtOAc/hexanes)