General procedure for the synthesis of 4-benzyloxy-3,5-dimethoxybenzaldehyde (5'-1) from benzyl bromide and butyraldehyde: Butyraldehyde (6.0 g, 32.9 mmol) and benzyl bromide (5.9 mL, 49.4 mmol) were dissolved in 70 mL of tetrahydrofuran (THF), and were added in batches to a solution containing potassium hydroxide (3.69 g, 65.8 mmol) in a 40mL of aqueous solution. A catalytic amount of tetrabutylammonium hydrogensulfate (Bu4NHSO4, 0.56 g, 1.6 mmol) was then added and the reaction mixture was stirred overnight at room temperature. After completion of the reaction, it was extracted with dichloromethane (CH2Cl2), the organic phases were combined, dried with anhydrous magnesium sulfate (MgSO4), filtered and concentrated under reduced pressure. Purification by silica gel column chromatography (cyclohexane/ethyl acetate, 85:15) afforded 4-benzyloxy-3,5-dimethoxybenzaldehyde (5'-1, 8.43 g, 31.0 mmol, 94% yield) in white solid form. The molecular formula of the compound is C16H16O4 and the molecular weight is 272.3 g-mol1. The analytical data are in agreement with those reported in the literature (Bennett C.J., Caldwell S.T., McPhail D.B., Morrice P.C., Duthie G.G., Hartley R.C., Bioorg. Med. Chem. 2004, 12, 2079-2098).
