A solution of 9.3 g (17.3 mmol) of benzothiophene-2-boronic acid trimeric anhydride in 100 cm3 of methanol and 400 cm3 of a 2N aqueous sodium carbonate solution are successively added to a solution of 22.36 g (47 mmol) of the levorotatory enantiomer of methyl (3aRS,4SR,7aRS)-2-benzyl-7-iodo-4-phenyl-1,2,3,4,5,7a-hexahydroisoindole-3a-carboxylate and of 6.03 g (5.2 mmol) of tetrakis(triphenylphosphine)palladium in 250 cm3 of 1,2-dimethoxyethane, the reaction mixture is then brought to reflux for two hours and stirring is maintained overnight at room temperature. After returning to a temperature in the region of 20° C., the reaction mixture is extracted with 800 cm3 of ethyl acetate and then the organic phase is washed with a saturated aqueous sodium chloride solution, dried over magnesium sulfate and concentrated under reduced pressure. The brown residue obtained is purified by flash chromatography on silica gel (230-400 mesh), elution being carried out with a cyclohexane/ethyl acetate (80/20 by volume) mixture. 11.04 g (50%) of the levorotatory enantiomer of methyl (3aRS,4SR,7aRS)-2-benzyl-4-phenyl-7-(2-benzothienyl)-1,2,3,4,5,7a-hexahydroisoindole-3a-carboxylate are thus obtained in the form of a yellow foam, the characteristics of which are as follows:
