Triethyloxonium tetrafluoborate (8.4 g) is added to a stirred suspension of 2-(2-methoxyphenyl)acetamide (6.6 g) in anhydrous dichloromethane (20 cc). Stirring of the reaction mixture is continued for 20 hours at ambient temperature. The mixture is cooled to +5° C. and a solution of (3aR,7aR)-7,7-diphenyl-4-perhydroisoindolone hydrochloride (9.8 g) and triethylamine (10.4 cc) in dichloromethane (60 cc) is then added. After the temperature has returned to ambient temperature, the reaction mixture is refluxed for 4 hours. It is then treated, after the temperature has returned to ambient temperature, with a 10% aqueous potassium carbonate solution (40 cc); the organic phase is washed with distilled water (20 cc), dried over magnesium sulphate and concentrated to dryness under reduced pressure (2.7 kPa). The residue is crystallized from acetonitrile (20 cc); the crystals obtained are drained, washed with acetonitrile (5 cc) and with isopropyl ether (10 cc) and dried. The crystals are recrystallized from acetonitrile (45 cc); the crystals obtained are drained and dried. (3aR,7aR)-2-[1-imino-2-(2-methoxyphenyl)ethyl]-7,7-diphenyl-4-perhydroisoindolone (3.8 g) melting at 191° C. is obtained. [α]D20 =-255° (c=1, methanol).
