Under argon, 102 mg (0.16 mmol) of [(4S)-4-{[tert-butyl(dimethyl)silyl]oxy}-7-cyclopentyl-5-(4-fluorophenyl)-2,2-dimethyl-3,4-dihydro-2H-chromen-6-yl][4-(trifluoromethyl)phenyl]methanone (Example 13A) are initially charged in 2 ml of abs. toluene and cooled to −78° C. 250 μl (0.25 mmol) of a diisobutylaluminum hydride solution (1 M in hexane) are slowly added dropwise, and the mixture is stirred at −78° C. After 30 min, another 80 μl (0.08 mmol) of diisobutylaluminum hydride solution (1 M in hexane) are added dropwise, and the mixture is stirred for another 30 min. 20% strength sodium/potassium tartrate solution is added, and the mixture is extracted repeatedly with ethyl acetate. The combined organic phases are washed with saturated sodium chloride solution, dried over sodium sulfate, filtered and concentrated. The crude product obtained is purified by preparative thick-layer chromatography on silica gel (mobile phase: cyclohexane/ethyl acetate 5:1). This gives 47 mg (46% of theory) of the title compound which is used in the next step without further characterization.
