[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([Cl:8])=[CH:4][C:3]=1[C:9]1([CH2:14][OH:15])[CH2:13][CH2:12][CH2:11][CH2:10]1.C(N(CC)CC)C.[S:23](Cl)([CH3:26])(=[O:25])=[O:24].C(OCC)(=O)C>ClCCl.CCCCCC.O>[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([Cl:8])=[CH:4][C:3]=1[C:9]1([CH2:14][O:15][S:23]([CH3:26])(=[O:25])=[O:24])[CH2:13][CH2:12][CH2:11][CH2:10]1
To a stirred solution of [1-(2,5-dichlorophenyl)-cyclopentyl]-methanol (200) (23 g, 95.04 mmol) in dry dichloromethane (250 mL) was added dry triethylamine (26.42 mL, 190.083 mmol) slowly, then mesyl chloride (8.785 mL, 114.05 mmol) was added and the mixture was stirred for 16 h at room temperature. Silica thin layer chromatography was performed (10% ethyl acetate in hexane, Rf=0.5) After completion of the reaction, the mixture was diluted with water, and extracted with dichloromethane. The combined organic layer was washed with brine, and dried over Na2SO4 and concentrated under reduced pressure. The resulting crude product was purified using normal silica gel (100-200 mesh) column chromatography using a gradient eluent of 2 to 10% ethyl acetate in hexane to get pure methanesulfonic acid 1-(2,5-dichlorophenyl)-cyclopentylmethyl ester (201) (24 g, 78.12%) as a white solid.
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