In a three-necked flask, 200mL of tetrahydrofuran, 35.0g of methyl 3-bromophenyl ethylcarbamate and 50mL of concentrated sulfuric acid were added, and the reaction was heated to reflux. At the end of the reaction, it was poured into 500mL of ice water, extracted with dichloromethane (150mL X 3 ), the combined organic phases were washed with water, washed with saturated brine, dried with anhydrous sodium sulfate, and concentrated to obtain 6-bromo-2-methoxycarbonyl-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid 38.9g (91.3%).
Synthesis of 6-bromo-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid: 35.0g of 6-bromo-2-methoxycarbonyl-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid and 200mL of 10M sulfuric acid were added into a triple-necked vial and reacted at reflux for 6 h. After the reaction, the pH was adjusted to 7 with sodium bicarbonate, cooled down, and a solid precipitated by filtration, which was dried to obtain 6- Bromo-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid 21.8g (76.4%).
