Hydrochloric Acid → Z-3-(3,5-Dimethoxyphenyl)-2-(4-hydroxyphenyl)-acrylic acid

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E-3-(3,5-dimethoxyphenyl)-2-(4-hydroxyphenyl)-acrylic acid, 7 (10.0 g, 33.3 mmol) was dissolved in a mixture of acetic anhydride (40 mL, 0.42 mole) and triethylamine (40 mL, 0.29 mole) and heated at 125° C. for 24 h. The mixture was cooled to room temperature. Ethyl acetate (150 mL) was added, further cooled to 5° C., acidified with concentrated HCl (30 mL) and stirred at this temperature for 90 min. The organic layer was separated and the aqueous layer was extracted with ethyl acetate (100 mL). The combined organic layers were washed with water (2×50 mL) and extracted with aqueous NaOH (5M, 3×70 mL). The aqueous alkaline layer was acidified with glacial acetic acid (65 mL) to pH 5.2 and stirred at 0° C. for 30 min. Solid that separated was filtered and mother liquor was acidified with concentrated HCl (90 mL) and stirred at 5° C. for 1 h. Solid that separated was filtered, washed with cold water (2×50 mL) and dried at 45° C. for 6 h to yield, 19, (1.3 g, 13%): mp 135-137° C.; 1HNMR (400 MHz, DMSO-d6) δ 13.28 (br, 1H), 9.70 (br, 1H), 7.32 (d, J=10.4 Hz, 2H), 6.81(s, 1H, overlapped), 6.79 (d, J=9.7 Hz, 2H), 6.67 (d, J=2.5 Hz, 2H), 6.64 (t, J=2.5 Hz, 1H), and 3.73 (s, 6H); MS (EI) m/z 299[M]−.

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