Methanol → HCID 12289779, Verbindung

A solution of methyl 5-bromo-4-tert-butyl-furan-2-carboxylate (1.45 g, 5.57 mmol, prepared as described in the previous step) in a mixture of THF (15 mL), MeOH (10 mL), and H2O (5 mL) was treated with 3 M aqueous NaOH solution (3.00 mL, 9.00 mmol) and the resulting mixture was stirred at room temperature for 16 h. The solvent was removed under reduced pressure and the residue was dissolved in H2O (60 mL) and extracted with Et2O (2×30 mL). The aqueous layer was acidified to pH-2 using 2 M HCl. The precipitate was isolated by filtration, washed with H2O (20 mL), and air-dried to yield 5-bromo-4-tert-butyl-furan-2-carboxylic acid. The filtrate was extracted with EtOAc (3×20 mL) and the combined extracts were dried over MgSO4 and filtered. The solvent was removed under reduced pressure to yield a second crop of 5-bromo-4-tert-butyl-furan-2-carboxylic acid. 1H-NMR (400 MHz, CDCl3) δ: 7.25 (s, 1H), 1.35 (s, 9H).