2,4-Pentanedione (3 g, 30.0 mmol) and boronic anhydride (1.46 g, 21.0 mmol) were dissolved in ethyl acetate (30 ml) and heated and stirred at 45°C for 30 minutes. Subsequently, 3,4-dimethoxybenzaldehyde (9.96 g, 59.9 mmol) and tributyl borate (13.79 g, 59.9 mmol) were added and stirring was continued at 45°C for 30 min. Butylamine (4.44 ml, 44.9 mmol) dissolved in ethyl acetate (30 ml) was added slowly and dropwise over 15 minutes and the reaction mixture was stirred at 45°C for 16 hours. After completion of the reaction, an aqueous HCl solution prepared from 25.5 ml of water and 4.5 ml of concentrated hydrochloric acid was added, and the two-phase mixture was heated with stirring at 60°C for 1 hr. The organic layer was separated and the aqueous layer was extracted with ethyl acetate (50 ml). The organic phases were combined, washed sequentially with water, saturated sodium chloride solution, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give a red oily crude product (10.42 g). The crude product was purified by silica gel column chromatography with ethyl acetate:hexane (50:50) as eluent to afford (1E,6E)-1,7-bis(3,4-dimethoxyphenyl)hepta-1,6-diene-3,5-dione as an orange solid (4.0 g, 34% yield). HPLC-UV analysis showed purity >97%.1H NMR (60 MHz, CDCl3) δ: 16.05 (1H, bs), 7.59 (2H, d), 6.76-7.26 (6H, m), 6.45 (2H, d), 5.79 (1H, s), 3.91 (6H, s), 3.89 (6H, s).
