Formic Acid → 6-Methoxy-3,4-dihydroisoquinoline

In tetrahydrofuran (100 ml), 3-methoxyphenethylamine (75.0 g) was dissolved. To the resulting solution, formic acid (60 ml) and acetic anhydride (108 ml) were added under ice cooling, followed by stirring overnight at room temperature. A saturated aqueous solution of sodium bicarbonate was added to the reaction mixture to separate the organic layer. The organic layer was washed with saturated aqueous NaCl solution and then dried over anhydrous sodium sulfate. The residue obtained by distilling off the solvent under reduced pressure was dissolved in benzene (200 ml), followed by the dropwise addition of phosphorus oxychloride (140 ml) under ice cooling. After stirring at 70° C. for 15 minutes, the reaction mixture was successively added with ice and 2N hydrochloric acid. The resulting mixture was stirred for 1 hour under ice cooling. The water layer was separated from the reaction mixture, neutralized with potassium carbonate and then extracted with dichloromethane. The extract was dried over anhydrous sodium sulfate. The residue obtained by distilling off the solvent under reduced pressure was purified by chromatography on a silica gel column (dichloromethane˜dichloromethane:methanol=100:1), whereby the title compound (13.5 g, 17%) was obtained.