N-benzyloxycarbonyl-p-chloroanilinoacetaldehyde diethyl acetal (10 g) and 3,4-dihydroxyphenethylamine hydrochloride (4.2 g) were added to a mixture of n-butyl alcohol (100 ml) and water (14 ml) and then the mixture was refluxed for 4 hours. The above-mentioned acetal (1 g) was added to the mixture and the resultant mixture was refluxed for 4 hours. The reaction mixture was concentrated to dryness under reduced pressure and the residue was washed with ethyl acetate and collected by filtration. The crystals were recrystallized from a mixture of methanol and ether to give 1-(N-benzyloxycarbonyl-p-chloroanilinomethyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline hydrochloride (7.0 g), mp 210° to 212° C. (dec.).
