[CH2:1]([O:8][C:9]1[CH:14]=[CH:13][C:12]([CH2:15][C@H:16]([OH:20])[C:17]([OH:19])=[O:18])=[CH:11][CH:10]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.CO[C:23](OC)([CH3:25])[CH3:24].C1(C)C=CC(S([O-])(=O)=O)=CC=1.[NH+]1C=CC=CC=1>C(Cl)(Cl)Cl.O>[CH2:1]([O:8][C:9]1[CH:14]=[CH:13][C:12]([CH2:15][C@@H:16]2[O:20][C:23]([CH3:25])([CH3:24])[O:18][C:17]2=[O:19])=[CH:11][CH:10]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1
(S)-3-(4-Benzyloxy-phenyl)-2-hydroxy-propionic acid (2.0 g, 7.34 mmol), 2,2-dimethoxypropane (18.63 g, 0.179 mol) and pyridinium p-toluene sulfonate (0.92 g, 3.66 mmol) in chloroform (80 mL) was heated to reflux for 40 minutes under N2. The mixture was cooled, diluted with water, and extracted with CH2Cl2. The organic layer was dried (Na2SO4) and concentrated in vacuo to give crude product that was purified by flash chromatography using 10:1 hexanes:acetone to afford the title compound (2.01 g, 88%). 1H-NMR (400 MHz, CDCl3) δ 7.43–7.29 (m, 5H), 7.17 (d, 2H, J=8.80 Hz), 6.91 (d, 2H, J=8.80 Hz), 5.04 (s, 2H), 4.61 (dd, 1H, J=6.36 Hz, J=4.40 Hz), 3.12 (dd, 1H, J=14.617 Hz, J=4.40 Hz), 2.99 (dd, 1H, J=14.67 Hz, J=6.36 Hz), 1.49 (s, 3H), 1.36 (s, 3H). MS (ES+) m/z calc'd for C19H20O4 (M+NH4) 330. Found m/z 330.
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