To a pre-cooled to 0 °C solution of 1 (100.0 g, 0.381 mol) in THF (1.5 L) neat t-BuOK (85.6 g, 0.763 mol) was added in several portions keeping the temperature below 5 °C. The reaction mixture was warmed up to rt and stirred for an additional 4 h, then concentrated under reduced pressure. The residual brownish solid was dissolved in water (350 mL), acidified with NaHSO4 (45.7 g, 0.381 mol) and extracted with CHCl3 (4×350 mL). Combined organic phases were dried over Na2SO4 and evaporated under reduced pressure. The crude product was dissolved in THF (250 mL) and acidified with anhydrous HCl (ca. 3.6 M in dioxane, 110 mL). The precipitate was filtered and dried under a high vacuum (1 mmHg) to give 8. Yield 85.4 g, 0.320 mol, 84%.