Step 4:Preparation of intermediate 7
Intermediate 6 (0.48g, 1.75mmol, 1.0 eq) and MeCN (9mL, c=0.2) was added in sealed tube. To this solution, EtI (2mL, 14.0 eq) was added. After addition, the reaction mixture was stirred at 90℃ for 10h. After completion, the reaction mixture was concentrated under reduce pressure. The residue was purified by column chromatography to give intermediate 7 (470mg, yield=62.6%, HPLC: 99%) as a solid.