The general procedure for the synthesis of (3R,5aS,6R,8aS,9R,10S,12R,12aR)-3,6,9-trimethyldecahydro-3H-3,12-epoxy[1,2]dioxahepta[4,3-i]isochromene-10-ol from artemisinin was carried out as follows: under nitrogen protection, a solution of LiBHEt3 (a 1 M solution of tetrahydrofuran) was passed through a syringe was slowly added dropwise to a solution of artemisinin (200 mg, 0.71 mmol) dissolved in anhydrous tetrahydrofuran (20 mL). The temperature of the reaction mixture was maintained constant during the reaction by means of a water or ice water bath. The progress of the reaction was monitored by thin layer chromatography (TLC) until the artemisinin was completely consumed (about 5-10 min). Subsequently, THF solution of acetic acid (20 vol%, 100 μL or 50 μL at a time) was added in batches to quench the reaction and the pH of the reaction mixture was adjusted to 5-6. The reaction mixture was concentrated to dryness under reduced pressure. The dried residue was separated by extraction with ethyl acetate and distilled water. After separation of the organic phase, the aqueous phase was extracted twice more with ethyl acetate. All ethyl acetate extracts were combined and dried with anhydrous sodium sulfate for 6 hours. The dried organic phase was filtered and concentrated to dryness under reduced pressure to give a white flaky target product.
