A solution of (3aR,7aR)-7,7-diphenyl-4-perhydroisoindolone hydrochloride (2.12 g), triethylamine (0.9 cc) and pyridine (0.5 cc) in dichloromethane (30 cc) is added, at 0° C., to a solution of (S)-α-fluorophenylacetyl chloride [prepared from acid (1 g) by the method described by S. Hamman et al., J. Fluorine Chem., 37, 85 (1987)] in dichloromethane (20 cc). The reaction mixture is stirred for 2 hours allowing the temperature to return to 20° C. and is then concentrated to dryness under reduced pressure (2.7 kPa). The residue is taken up in ethyl acetate (100 cc). The solution is washed with water (2×100 cc) and then with saturated sodium bicarbonate solution (50 cc) and with saturated sodium chloride solution (50 cc), dried over magnesium sulphate and filtered and the filtrate is concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a silica gel column (particle size 0.2-0.063 mm, diameter 3 cm, height 40 cm), eluting under a nitrogen pressure of 0.7 bar with ethyl acetate and collecting 100 cc fractions to give (3aR,7aR)-2-[(S)-α-fluorophenylacetyl]-7,7-diphenyl-4-perhydroisoindolone (1 g) in the form of a white meringue.
