To a stirred solution of 6-benzyloxy-7-methoxy-1-(3-methoxy-benzyl)-isoquinoline-4-carbaldehyde (90 mg, 0.22 mmol) in acetic acid (3 mL) was added selenium dioxide (120 mg, 1.08 mmol). The reaction mixture was heated at 120° C. for 1 hr. The solvent was evaporated and the residue was diluted with dichloromethane (30 mL). The organic layer was washed with saturated aqueous sodium bicarbonate solution (20 mL), saturated aqueous sodium chloride solution (20 mL), dried over anhydrous magnesium sulfate, filtered and concentrated in vacuo to afford a crude oil. Flash chromatography (Merck Silica gel 60, 70–230 mesh, 40% ethyl acetate/hexane) afforded 6-benzyloxy-7-methoxy-1-(3-methoxy-benzoyl)-isoquinoline-4-carbaldehyde as a yellow solid (50 mg, 57% yield).
