An amount of 1.42 g of 2-methylthio-5-(6-methoxycarbonylhexylidene-4-(3-t-butyldimethylsilyloxy-1-octenyl)-2-cyclopentenone obtained in Example 22 was added to a mixture of acetic acid (2.1 ml), tetrahydrofuran (1.4 ml) and water (0.7 ml), and the mixture was stirred at room temperature for 2 days. To the reaction mixture saturated aqueous sodium hydrogencarbonate and ethyl acetate were added, and the product was extracted into the organic layer. The extract was washed with saturated aqueous sodium chloride, then dried over anhydrous magnesium sulfate and filtered, followed by concentration. The concentrate was subjected to silica gel chromatography to give 0.93 g (yield 85%) of 2-methylthio-5-(6-methoxycarbonylhexylidene)-4-(3-hydroxy-1-octenyl)-2-cyclopentenone.
