[O:1]1CCC[CH2:3][CH:2]1[O:7][C@@H:8]1[CH2:12][C@H:11]([O:13]C(=O)C)[CH:10]=[CH:9]1.C1(C)C=CC(S(O)(=O)=O)=CC=1.C(=O)([O-])[O-].C(=O)(O)[O-]>C(O)C.C(Cl)(Cl)Cl>[C:2]([O:7][C@@H:8]1[CH2:12][C@H:11]([OH:13])[CH:10]=[CH:9]1)(=[O:1])[CH3:3]Dissolve (-)-acetic acid cis-4-(tetrahydro-pyran-2-yloxy)-cyclopent-2-enyl ester (192 mg, 0.85 mmol, prepared in example 11) in ethanol (1.5 mL) and treat with p-toluenesulfonic acid (11.7 mg). Stir the reaction at room temperature for 2 hours. Add carbonate or bicarbonate to neutralize the reaction mixture and concentrate under vacuum. Purify the residue by chromatography (silica gel, 3 g, 1.5×3 cm column, 33% ethyl acetate/hexane, 80 mL), to provide the title compound (90 mg, 75% yield, 91% ee), [α]20D =-66.1°, (c=0.63, chloroform).
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