Acetic anhydride (74 μL, 0.79 mmol) was added to a solution of phenstatin (3b, 0.2 g, 0.63 mmol), DMAP (7.8 mg, 0.063 mmol) and triethylamine (0.13 mL, 0.94 mmol) in dry methylene chloride (1.5 mL, under argon at room temperature). The yellow solution was stirred for 30 min (reaction was complete by TLC). Methanol (5 Ml) was added and the reaction mixture concentrated to a solid that was washed with diethyl ether (3 ×10 mL) and partitioned between ethyl acetate and cold Ln hydrochloric acid. The organic layer was washed with 10% aqueous sodium bicarbonate and dried. Solvent removed, in vacuo, gave an off-white solid that was recrystallized from ethyl acetate-hexane to give colorless snowflakes of analytical purity: EIMS m/z (peak height) 360 M+, 60%), 318 (100%), 303 (10%), 195 (20%), 151 (30%), 91 (32%), 44 (25%). 1H-NMR (CDCl3)δ H 7.740 (1H, dd, J6/2 2.1 Hz, J6/5 8.1 Hz, H-6). 7.556 (1H, d, J2/6 2.1 Hz, H-2), 7.026 (1H, d, J5/6 8.0 Hz, H-5), 7.013 (2H, s, H-2′, 6′), 3.914 (3H, s, 4-OCH3), 3.907 (3H, s, 4′-OCH3), 3.863 (6H, s, 3′, 5′-OCH3), 2.315 (3H, s, —OCOCH3).
