A solution of [2-fluoro-4-(8-hydroxy-2,2,4,4-tetramethyl-chroman-6-ylethynyl)-phenyl]-acetic acid methyl ester (Intermediate 21, 0.037 g, 0.0493 mmol) in methanol (2 mL) and tetrahydrofuran (1 mL) was treated with a 2M solution of potassium hydroxide (2 mL, 4 mmol) and the resulting reaction mixture was stirred at ambient temperature for 2 h. The volatiles were evaporated in vacuo to a residue that was neutralized with saturated aqueous ammonium chloride solution and extracted with ethyl acetate. The organic phase was washed with water and brine, and dried over anhydrous magnesium sulfate, filtered and evaporated in vacuo to afford the title product (0.024 g, 69%).
