To a solution of 0.78 g of (3aRS,4RS,6SR,7aSR)-4-(2-methoxyphenyl)-6-methyl-4-perhydroisoindolol in 80 cm3 of dichloromethane is added 0.5 cm3 of triethylamine. The reaction mixture is cooled to 5° C. and 0.54 g of (2-dimethylaminophenyl)acetic acid, 0.05 g of 1-hydroxybenzotriazole monohydrate and 0.63 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride are added. The reaction mixture is maintained for 1 hour at 5° C. and for 16 hours at 20° C. and is then washed twice with 100 cm3 of water, dried over magnesium sulphate, filtered and concentrated under reduced pressure (2.7 kPa). The residue is chromatographed on a column of silica gel (0.060-0.200 mm, diameter 4 cm, height 50 cm), eluting under a pressure of 0.7 bar with a mixture of dichloromethane and methanol [97.5/2.5 by volume] and collecting 65 cm3 fractions. Fractions 17 to 23 are concentrated and, after drying at 40° C. at 15 Pa, 0.90 g of (3aRS,4RS,6SR,7aSR)-4-(2-methoxyphenyl)-2-[(2-dimethylaminophenyl)acetyl]-6-methyl-4-perhydroisoindolol is obtained in the form of a white powder which is dissolved in 50 cm3 of dioxane. 3 cm3 of 5M hydrochloric acid solution in dioxane are added and, after 1 hour at room temperature, the solution is concentrated under reduced pressure (2.7 kPa), triturated in isopropyl ether, filtered and dried at 40° C. at 15 Pa. 1.0 g of (3aRS,4RS,6SR,7aSR)-4-(2-methoxyphenyl)-2-[(2-dimethylaminophenyl)acetyl]-6-methyl-4-perhydroisoindolol hydrochloride is obtained.
