[CH3:1][C:2]1[C:10]2[C:5](=[CH:6][CH:7]=[CH:8][CH:9]=2)[C:4]([CH3:12])([CH3:11])[CH:3]=1.[C:13](Cl)(=[O:15])[CH3:14].[Cl-].[Cl-].[Cl-].[Al+3]>ClCCCl>[C:13]([C:3]1[C:4]([CH3:12])([CH3:11])[C:5]2[C:10](=[CH:9][CH:8]=[CH:7][CH:6]=2)[C:2]=1[CH3:1])(=[O:15])[CH3:14]To a mixture of 20 g 1,3,3-trimethylindene (see e.g. J. Am. Chem. Soc. 76, 5430 (1954) ) 13 g acetyl chloride and 55 ml 1,2-dichloroethane in a nitrogen atmosphere was dosed with stirring 21.5 g aluminum trichloride over a period of one and a half hour and at a temperature of 20-25° C. After an additional stirring period of 30 minutes at 20° C. the mixture was poured on ice and stirred for another hour. The organic layer was washed with subsequently 5%-sodium carbonate solution, saturated sodium chloride solution and concentrated by means of a rotatory evaporator. Vacuum distillation of the residue yielded a 15.3 g of a fraction boiling up to 145° C. at 3 mm Hg. Recrystallization from methanol yielded 10 g 2-acetyl-1,3,3-trimethylindene of 99.8% purity, mp 104.5-105.0° C.
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