Methyl α-methylthio[m-(2-phenyl-1,3-dioxa-2-cyclopentyl)phenyl]acetate (6.88 g) was dissolved in 30 ml of anhydrous dimethyl sulfoxide. While cooling at 15° C., 810 mg (65% content) of sodium hydride was added, and the mixture was stirred for 1 hour. Hydrogen evolved gradually to form a reddish brown solution. While cooling at 15° C., 1.5 ml of methyl iodide was added to this solution, whereupon the color vanished immediately. After stirring for 5 minutes, an aqueous solution of ammonium chloride (2 g/10 ml) was added, and then 40 ml of water was added. The mixture was extracted first with 50 ml of diethyl ether, and then three times with 10 ml of diethyl ether. The extract was washed three times with 10 ml of water, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The residue was chromatographed on a column of Florisil using benzene and diethyl ether as eluents to afford 6.14 g of methyl α-methylthio-α-[m-(2-phenyl-1,3-dioxa-2-cyclopentyl)phenyl]propionate as a colorless oil in a yield of 86%.
