[CH3:1][O:2][C:3]1[CH:11]=[C:10]2[C:6]([CH2:7][CH2:8][C:9]2=[O:12])=[CH:5][CH:4]=1.[CH3:13][CH:14](O)[CH:15]=[CH2:16].COC(OC)(C)C.C1(C)C=CC(S(O)(=O)=O)=CC=1>C1(C)C=CC=CC=1>[CH2:13]([CH:8]1[CH2:7][C:6]2[C:10](=[CH:11][C:3]([O:2][CH3:1])=[CH:4][CH:5]=2)[C:9]1=[O:12])[CH:14]=[CH:15][CH3:16]A solution of 20.0 g of 6-methoxy-1-indanone, 31.3 ml of 3-buten-2-ol, 53.5 ml of 2,2-dimethoxypropane and 200 mg of p-toluenesulfonic acid in 200 ml of toluene was brought to boiling. The resulting methanol/acetone mixture was distilled off and the reaction solution was subsequently boiled under reflux overnight. After cooling, the solution was washed with 50 ml of saturated sodium hydrogen carbonate solution. The aqueous washing was extracted with 50 ml of ethyl acetate, the organic phases were combined, dried with magnesium sulfate and evaporated in a vacuum. Purification on silica gel (hexane/diethyl ether 5:1) yielded 13.6 g (55%) of (RS)-2-(2-buten-1-yl)-6-methoxy-1-indanone as a pale yellow oil.
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