1-Bromo-4-tert-butyldimethylsiloxy-3-methoxy-6-(2-methoxyethylidene)-benzene (AP-15): 200 mg (0.54 mmol) AP-15 was stirred vigorously for 24 hours in 20 mL of tetrahydrofuran: 90% formic acid aqueous solution (4:1). The mixture was then combined with 20 mL of water, and the tetrahydrofuran was distilled off. The residue was extracted three times with 20 mL of ethyl acetate. The combined organic phases were washed with about 20 mL of saturated sodium bicarbonate aqueous solution until neutral, and then washed with 20 mL of ethyl acetate by shaking. The combined organic phases were dried over sodium sulfate, filtered, and evaporated. Subsequent column chromatography (15 g silica gel, eluent: petroleum ether: ethyl acetate = 2:1) yielded 20 mg (15% of theoretical value) of colorless L1 crystals and 40 mg of 6-bromoisovanillin (32% of theoretical value) of colorless AP-28 crystals, melting point 106–108 °C.
Figure 2-Bromoisovanillin Synthetic Route
