(5R,5aR,8aR,9R)-9-Hydroxy-5-(3,4,5-trimethoxyphenyl)-5,5a,8a,9-tetrahydrofuro[3',4':6,7]naphtho[2,3-d][1,3]dioxol-6(8H)-one (onychocercazylidene, 2.1 g, 5.0 mmol) was used as a raw material and dissolved in anhydrous dichloromethane. Sodium iodide (2.3 g, 15.0 mmol) was added to this solution and stirred for 5 min. The reaction mixture was cooled to 0°C (ice-water bath) and methanesulfonic acid (1.48 mL, 15.0 mmol) was added slowly dropwise, after which stirring was continued and gradually brought to room temperature. The reaction was continued at room temperature for 5 hours, during which time nitrogen was introduced to remove the HI gas generated from the reaction. After completion of the reaction, the solvent was removed by concentration under reduced pressure. The crude product was dissolved in a solvent mixture of acetone-water (25 mL-25 mL), barium carbonate (2.0 g, 10.0 mmol) was added, and the reaction was carried out at 40 °C for 30 min. The reaction solution was diluted with dichloromethane (100 mL), poured into 500 mL of 10% aqueous sodium thiosulfate solution and extracted with dichloromethane. The organic phases were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to obtain the crude product. The crude product was purified by silica gel column chromatography (eluent: chloroform:methanol=92:8) to afford the target product (5R,5aR,8aR,9S)-9-hydroxy-5-(4-hydroxy-3,5-dimethoxyphenyl)-5,5a,8a,9-tetrahydrofuro[3',4':6,7]naphtho[2,3-d][1,3]dioxolan-6(8H)-one ( VII, 1.8g, 90% yield), as white solid.
