[CH2:1]([CH:4]1[C:8]([OH:10])([CH3:9])[CH:7]=[CH:6][C:5]1=[O:11])[CH:2]=[CH2:3].N1C=CC=CC=1.ClCCl.[C:21](Cl)(=[O:23])[CH3:22]>O>[C:21]([O:10][C:8]1([CH3:9])[CH:7]=[CH:6][C:5](=[O:11])[CH:4]1[CH2:1][CH:2]=[CH2:3])(=[O:23])[CH3:22]Into a flask equipped with a stirrer and a thermometer, dl-2-allyl-3-hydroxy-3-methyl-4-cyclopentenone (30.4 g), pyridine (30 g) and dichloromethane (300 g) were charged, and acetyl chloride (30 g) was dropwise added thereto at a temperature from 10° to 20° C. in 2 hours. Then, stirring was continued at a room temperature for 24 hours. To the reaction mixture kept below 10° C., water (100 ml) was added to decompose excess of acetyl chloride. From the resultant mixture, the organic layer was separated and washed with 1% hydrochloric acid, 1% sodium bicarbonate solution and water in order. Removal of the solvent by distillation gave dl-3-acetoxy-2-allyl-3-methyl-4-cyclopentenone (36.5 g). Yield, 94%.
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