[Al+3].[Cl-].[Cl-].[Cl-].[CH3:5][CH:6]1[C:18](=[O:19])[C:9]2=[CH:10][C:11]3[CH2:12][CH2:13][CH2:14][CH2:15][C:16]=3[CH:17]=[C:8]2[CH2:7]1.[Br:20]Br.O>ClCCl>[Br:20][C:17]1[C:16]2[CH2:15][CH2:14][CH2:13][CH2:12][C:11]=2[CH:10]=[C:9]2[C:18](=[O:19])[CH:6]([CH3:5])[CH2:7][C:8]=12
To a mixture of 43.0 g (322 mmol) of AlCl3 in 50 ml of dichloromethane, a solution of 26.4 g (132 mmol) of 2-methyl-2,3,5,6,7,8-hexahydro-1H-cyclopenta[b]naphthalen-1-one in 25 ml of dichloromethane was added dropwise, while vigorously stirring, over 10 min at 0° C. Then, 6.8 ml (21.1 g, 132 mmol) of bromine was added dropwise over 1 h at this temperature. The resulting mixture was stirred overnight at this temperature and then added to 400 ml of cold water. The organic layer was separated, and the aqueous layer was extracted with 3×150 ml of methyl-tert-butyl ether. The combined organic fractions were washed with aqueous Na2CO3, dried over K2CO3, and evaporated to dryness. Fractional distillation gave the title product, b.p. 165-175° C./1 mm Hg. Yield 19.3 g (53%) of yellowish oil.
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