A mixture of 1-[1-(4-chlorophenyl)cyclobutyl]-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (7.29 g prepared as described in Example 50), ethyl iodide (1.76 ml), anhydrous potassium carbonate (5.52 g) and acetone (100 ml) was heated under reflux for 16 hours. The reaction mixture was filtered and the solvent was removed by evaporation to give a residue which was digested with a 9:1 mixture of petroleum ether and triethylamine. The solution was filtered and the solvent removed to give a residue. A sample of this residue (4 g) was heated under reflux in a nitrogen atmosphere with glacial acetic acid (40 ml) and 48% hydrobromic acid (40 ml) for 20 hours. Removal of the solvent gave a residue which was dried by azeotropic distillation with industrial methylated spirit, then with propan-2-ol and finally with a mixture of toluene and propan-2-ol to give a solid which was washed with propan-2-ol and dried in vacuo at 80° C. to give 1-[1-(4-chlorophenyl)cyclobutyl]-2-ethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline hydrobromide, m.p. 213°-215° C.
