To a solution of compound 5/methanol from Step 2B were added methanol (6.4 vol) and 30% sodium methoxide/methanol solution (2.0 equiv.). The mixture was heated to 50 °C and stirred at 50 °C for 3 h. The reaction mixture was concentrated under reduced pressure to 7.0 vol. After water (4.6 vol) was added to the obtained concentrate, the mixture was adjusted to acidic condition with 35% hydrochloric acid. After the resulting slurry was stirred at 25 °C for 2 h, 35% hydrochloric acid (2.4 equiv.) was added to the slurry. The slurry was stirred at 25 °C for 1 h and filtrated. The filtrated solid was washed with a mixture of methanol (0.7 vol) and water (2.9 vol). The obtained solid was dried under reduced pressure at 80 °C to afford compound 6 (85% yield). Step 3 (vol, wt, and equiv. were based on the amount of compound 6)