[CH2:1]([C:3]1[CH:11]=[C:10]2[C:6]([CH2:7][CH2:8][C:9]2=[O:12])=[CH:5][CH:4]=1)[CH3:2].[CH3:13][CH:14](O)[CH:15]=[CH2:16].C1(C)C=CC(S(O)(=O)=O)=CC=1.O>COC(OC)(C)C>[CH2:13]([CH:8]1[CH2:7][C:6]2[C:10](=[CH:11][C:3]([CH2:1][CH3:2])=[CH:4][CH:5]=2)[C:9]1=[O:12])[CH:14]=[CH:15][CH3:16]A solution of 11.8 g of 6-ethyl-1-indanone, 15.4 ml of 3-buten-2-ol and 110 mg of p-toluenesulfonic acid in 110 ml of 2,2-dimethoxy-propane was boiled under reflux for 46 hours on a water separator filled with molecular sieve (0.4 nm, 2 mm pearl shaped). The reaction mixture was subsequently concentrated in a vacuum and purified by column chromatography on silica gel (hexane/diethyl ether 5:1). 7.92 g (50%) of (RS)-2-(2-buten-1-yl)-6-ethyl-1-indanone were obtained as a yellow oil.
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