BrCBr.O1CCC[CH2:5]1.[OH:9][C@H:10]1[CH2:14][C:13](=O)[C:12]([CH2:16][C:17]#[CH:18])=[C:11]1[CH3:19].C(=O)(O)[O-].[Na+]>ClCCl.[Zn].[Ti](Cl)(Cl)(Cl)Cl.O.CCCCCC>[CH3:19][C:11]1[C@@H:10]([OH:9])[CH2:14][C:13](=[CH2:5])[C:12]=1[CH2:16][C:17]#[CH:18]Dibromomethane (1.3 g) and zinc dust (1.5 g) were added to dry tetrahydrofuran (20ml), and the resulting mixture was cooled to 0°~5° C. A dichloromethane solution (5 ml) of 1M titanium tetrachloride was added to the tetrahydrofuran solution over about 10 min, and the resulting mixture was allowed to react for 3 days at 0°5° C. Then a solution of (S)-4-hydroxy-3-methyl-2-(2-propynyl)cyclopent-2-ene-1-one (675 mg) in dichloromethane (10 ml) was added at 0°~5° C. over about 10 min. After the resulting mixture was allowed to react for 2 hours at the same temperature, hexane (40 ml) and then a slurry consisting of sodium bicarbonate (8 g) and water (4 ml) were added. After stirring for 2 hours at 0°~5° C., the organic layer was separated by decantation. The obtained residue was extracted three times with n-hexane (20 ml). The combined organic layer was washed with saturated aqueous sodium bicarbonate solution, and dried over anhydrous magnesium sulfate. Then the solvent was evaporated under reduced pressure, and the resultant residue was subjected to silica gel column chromatography (eluent; n-hexane: ethyl acetate=3:1) to afford the desired product, (S)-2-methyl-4-methylidene-3-(2-propynyl)cyclopent-2-ene-1-ol (17 mg, yield 2.6% as a pale yellow oil.
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