The (3R)-7-methoxy-3-(4-methoxyphenyl)-3-methylthiochroman-4-one prepared in Example 1 (11.4 g, 36.26 mmol) was dissolved in tetrahydrofuran (40 ml) and ethanol (20 ml). To this solution, sodium borohydride (2.74 g, 72.51 mmol) was added at −78° C., and the resulting mixture was stirred for 15 hours at room temperature. After the reaction was completed, dichloromethane, methanol and saturated aqueous sodium chloride were added to the reaction mixture, which was then extracted under heating conditions. The organic layer was dried over anhydrous magnesium sulfate. After distilling off the solvent, allyltrimethylsilane (10.74 ml, 67.6 mmol) and zinc iodide (12.9 g, 40.57 mmol) were added to a solution of the residue in dichloromethane (300 ml) followed by stirring for 15 hours at room temperature. Water was added to the reaction mixture, which was then extracted with dichloromethane. The organic layer was washed with saturated aqueous ammonium chloride and dried over anhydrous magnesium sulfate, and the resulting residue was purified by silica gel column chromatography (eluent: ethyl acetate/hexane=1/90) to give (3S,4S)-7-methoxy-3-(4-methoxyphenyl)-3-methyl-4-(2-propenyl)thiochroman (7.2 g, Yield 58%) as an oil.
