6,7-Dimethoxy-3,4-dihydroisoquinoline hydrochloride is used in the synthesis of Tetrabenazine (T284000).
First, 3,4-dimethoxyphenethylamine (18.1 g, 0.1 mol) and ethyl formate (22.1 g) were added to a 100 mL three-necked flask protected by nitrogen, and the reaction was held at 60 C with stirring for 24 hours. Decompression and concentration to obtain N-(3,4-dimethoxyphenethyl)formamide crude product. The above crude product was dissolved in 180 mL of dichloromethane, phthaloyl dichloride (20.3 g, 0.1 mol) was added, and the reaction was stirred at 20C for 4 h. The solid was gradually precipitated. Cooled to 10 , filtered to obtain 6,7-dimethoxy-3,4-dihydroisoquinoline hydrochloride crude product (mother liquor was washed twice with 50mL water, concentrated to recover dichloromethane, the residue was added to 100mL water, filtered to recover phthalic anhydride). Add the above crude product to isopropanol (180mL), heating to 70 , stirring 0.5-1h until all the solids are dissolved; add activated charcoal 1.8g, 80 continue to stir for 2-3h, 50 keep warm and filtration, filtrate re-warming to 70 , stirring for 0.5h; naturally cooled to 20 , it takes about 2h, filtration to get 6,7-dimethoxy-3,4-dihydroisoquinoline hydrochloride The finished product was 19.0 g. Yield 83%, HPLC purity 99.61%.
