[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[S:12][C:11]([CH2:13][CH3:14])=[C:10]([CH:15]([C:17]3[O:18][CH:19]=[CH:20][CH:21]=3)O)[CH:9]=2)=[CH:4][CH:3]=1.CC(C)=[O:24]>O>[Cl:1][C:2]1[CH:3]=[CH:4][C:5]([C:8]2[S:12][C:11]([CH2:13][CH3:14])=[C:10]([CH:15]3[C:17](=[O:24])[CH:21]=[CH:20][CH:19]3[OH:18])[CH:9]=2)=[CH:6][CH:7]=1To a solution of [5-(4-chloro-phenyl)-2-ethyl-thiophen-3-yl]-furan-2-yl-methanol (2.52 g, 7.9 mmol) in acetone (30 ml) and water (5 ml) is added polyphosphoric acid (0.5 ml) and the resulting solution heated at 60° C. for 5 hours. The resulting black solution is concentrated in vacuo and purified by flash chromatography on silica gel to give 5-[5-(4-chloro-phenyl)-2-ethyl-thiophen-3-yl]-4-hydroxy-cyclopent-2-enone as a clear gum (320 mg)
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