Synthesis
Step 1) Synthesis of Compound 9-2
Compound 9-1 (11.0 g, 44.8 mmol) was dissolved in DCM (200 mL). Et2NSF3 (8.85 mL, 67.3 mmol) was slowly added dropwise at -78 °C. After the addition was complete, the reaction was kept at a constant temperature for 2.0 hours, and then reacted at room temperature for 19 hours.
After the reaction was complete, ammonium chloride aqueous solution (100 mL) was added to quench the reaction. The aqueous layer was extracted with DCM (100 mL × 3). The organic phases were combined, washed with saturated brine, dried over anhydrous Na2SO4, concentrated, and purified by column chromatography (eluent: PE/EtOAc(v/v) = 20/1) to obtain 7.75 g of pale yellow liquid, yield: 70%.
Step 2) Synthesis of compound 9-3
Compound 9-2 (5.83 g, 23.6 mmol) was dissolved in THF (30 mL). At 0 °C, an aqueous solution of lithium hydroxide (1.98 g, 30 mL) was slowly added dropwise. After the addition was complete, the reaction was allowed to proceed at room temperature for 2.0 hours. After the reaction was complete, the pH of the reaction solution was adjusted to 5 with dilute hydrochloric acid (1M). After removing THF, the pH of the aqueous layer was adjusted to 2 with dilute hydrochloric acid (1M). The solution was extracted with EtOAc (80mL×3). The organic phases were combined, washed with saturated brine, dried over anhydrous Na2SO4, and concentrated to give 5.27g of white solid. Yield: 96%.
