To a stirred suspension of 4-methoxyphenethylamine (50.4 g, 0.33 mol, 1.0 eq.) in water (40 mL) was slowly added 37% aqueous formaldehyde (27.5 mL, 1.1 eq.) with continuous stirring for 20 minutes. Subsequently, concentrated hydrochloric acid (80 mL) was added dropwise to the reaction mixture and the mixture was heated to reflux and maintained for 1 hour. Upon completion of the reaction, the mixture was cooled to room temperature and concentrated to dryness in a rotary evaporator. The resulting residue was purified by recrystallization from acetone to afford 6-methoxy-1,2,3,4-tetrahydroisoquinoline hydrochloride as a white solid (60.1 g, 90% yield). The product did not require further purification and could be used directly in the subsequent reaction. Mass spectrometry analysis showed that the MH+ peak was located at 164.
