反応手順
A solution of 2,4,5-Trimethoxyphenylpropane (5 g) in 70 mL of dry dioxane was placed in 100 ml round bottom flask. To this was added a catalytic amount of acetic acid (2-4 drops) and 16 g of DDQ and finally started refluxing the mixture at 50 to 140° C. for 5 to 9 hrs. The solution, which was initially deep green, turned into pale yellow with the formation of hydroquinone (DDQH2). The mixture was cooled and the solid DDQH2 was filtered and further washed with chloroform. The filtrate and washings were combined and evaporated under reduced pressure. The product was taken in ether (80 ml) and the ether layer was washed with aqueous NaOH (15%, 2×15 ml). The combined aqueous layers are further extracted with ether (3×15 ml). The ether layers were combined and washed with saturated sodium chloride (3×15 ml), dried over anhydrous sodium sulphate and filtered. The solvent was removed to afford a crude yellow liquid which was loaded on silica gel column and the column was eluted with hexane (70-80 ml) and then with an increasing amount of hexane/ethyl acetate (9:1 to 1:9). The fractions were monitored on TLC plate and the desired fractions were combined and solvent was removed under vacuum to afford 2,4,5-trimethoxycinnamaldehyde in 82% yield as a yellow solid; mp 140° C.; UV (MeOH) λmax 244, 298, 366 nm; IR (film) νmax 1648 (conjugated carbonyl), 1602, 1504, 1466, 1448, 1350, 1254, 1120, 1024, 856 cm−1; 1H NMR δ 9.65 (1H, d, J=7.8 Hz, H-3′), 7.81 (1H, d, J=15.8 Hz, H-1′), 7.03 (1H, s, H-6), 6.64 (1H, dd, J=15.8 Hz, J=7.8 Hz, H-2′), 6.51 (1H, s, H-3), 3.95 (s, 3H, 2-OCH3), 3.91 (s, 3H, 4-OCH3), 3.87 (s, 3H, 5-OCH3); 13C NMR δ 194.1 (C-3′), 154.1 (C-1′), 153.2 (C-2), 147.6 (C-4), 143.3 (C-5), 126.4 (C-2′), 114.5 (C-1), 110.5 (C-6), 96.5 (C-3), 56.4 (5-OCH3), 56.2 (2-OCH3), 56.0 (4-OCH3); EIMS m/z 222 [M]+ (44), 207 (18), 191 (100), 179 (14), 171 (27), 151 (14), 147 (7), 69 (58), 58 (80).
