α-[[(2,3-dimethoxybenzyl)amino]methyl]-6-fluoro-3,4-dimethoxybenzyl alcohol (1.0 g) was dissolved in 7 ml of trifluoroacetic acid, and after adding thereto under ice cooling, conc. sulfuric acid (0.25 ml), the mixture was stirred for 40 minutes. 0.72 g of sodium acetate was added to the reaction mixture, and the mixture was concentrated. To the residue was added chloroform and water, and the mixture was basified by addition of conc. aqueous ammonia under ice cooling. After separating procedure, the chloroform layer was collected, washed with saturated aqueous NaCl solution, and dried over anhydrous sodium sulfate. The solvent was distilled off, 0.94 g of 4-(6-fluoro-3,4-dimethoxyphenyl)-7,8-dimethoxy-1,2,3,4-tetrahydroisoquinoline was obtained as a syrupy matter.
