To a solution of 4-acetylbenzoic acid (1.50 g, 9.1 mmol) and 5-(benzo[b]thien-2-yl)-2,4-dimethoxybenzaldehyde from Ex-3A (3.27 g, 11.0 mmol) in N,N-dimethylformamide (76 mL) was added a solution of sodium hydroxide (5 M, 7.3 mL, 36.5 mmol). The reaction mixture was allowed to stir at room temperature for 2 h and was then diluted with water to a volume of 150 mL. The solution was washed with dichloromethane and acidified with concentrated sulfuric acid to pH=3. The resulting solution was then extracted with dichloromethane. The dichloromethane extract was washed with brine, dried over sodium sulfate and concentrated. The resulting oily product solidified in ethanol. The solid was further stirred in ethanol for one day and collected by filtration. The solid was washed with ethanol, then dried in vacuo to afford the title compound as a yellow solid (2.2 g, 54%). 1H NMR (300 MHz, DMSO-d6) δ 8.36 (s, 1H), 8.21 (d, 2H), 8.07 (m, 3H), 7.93 (m, 3H), 7.82 (d, 1H), 7.32 (m, 2H), 6.86 (s, 1H), 4.08 (s, 3H), 4.00 (s, 3H). Anal. Calculated for C26H20O5S·1/6H2O: C, 69.78; H, 4.58; S, 7.17; found: C, 69.95; H, 4.69; S, 7.15. HPLC purity: 97.9% (area percentage).
