Reaction Steps
Under an N2 atmosphere, to a solution of (+)-(2R,3S)-5,7-dihydroxy-2-(3,4-dihydroxyphenyl)chroman-3-yl 4-hydroxybenzoate 11 (20 mg, 0.048 mmol) in pyridine (1 ml), acetic anhydride (0.2 ml) was added dropwise at 0° C. The reaction mixture was stirred at rt overnight. The excess pyridine was distilled under vacuum. The residue was purified by flash chromatograph on silica gel (EtOAc/n-hexane, 1/1 in v/v) to afford 22* (34 mg, 95% yield). mp: mp 149-151° C.; [α]D=+42.5 (c=1.2, CHCl3); 1H NMR (CDCl3, 400 MHz): δ 7.96 9d, J=8.7 Hz, 2H), 7.31 (A of ABq, J=8.4, 1.8 Hz, 1H), 7.26 (d, J=1.8 Hz, 1H), 7.21 (B of AB, J=8.4 Hz, 1H), 7.15 (d, J=8.7 Hz, 2H), 6.70 (d, J=2.2 Hz, 1H), 6.63 (d, J=2.2 Hz, 1H), 5.51 (dd, J=11.2, 6.0 Hz, 1H), 5.33 (d, J=6.0 Hz, 1H), 3.04 (A of ABq, J=16.8, 5.0 Hz, 1H), 2.83 (B of ABq, J=16.8, 6.0 Hz, 1H), 2.31 (s, 3H), 2.29 (s, 3H), 2.28 (s, 3H), 2.27 (s, 6H); 13C NMR (CDCl3, 400 MHz): δ 168.8, 168.7, 168.3, 167.9, 164.8, 154.5, 154.3, 149.8, 149.4, 142.2, 142.1, 136.1, 131.3, 126.9, 124.3, 123.7, 122.0, 121.6, 121.3, 110.0, 108.7, 107.6, 77.7, 69.1, 23.9, 21.0, 20.7, 20.5; HRMS (ESI) calcd for C32H28O13Na (M+Na) 643.1428; found 643.1437.
