[Br:1]Br.[Cl:3][C:4]1[CH:5]=[C:6]([C:11]2([C:15](=[O:17])[CH3:16])[CH2:14][CH2:13][CH2:12]2)[CH:7]=[CH:8][C:9]=1[Cl:10]>ClCCl.CO>[Br:1][CH2:16][C:15]([C:11]1([C:6]2[CH:7]=[CH:8][C:9]([Cl:10])=[C:4]([Cl:3])[CH:5]=2)[CH2:14][CH2:13][CH2:12]1)=[O:17]A solution of bromine (10.2 ml) in dichloromethane (50 ml) was added dropwise over 3.5 hours at 10-15° C. under nitrogen to a stirred solution of 1-[1-(3,4-dichlorophenyl)cyclobutyl]ethanone (47 g) in a mixture of methanol (75 ml) and dichloromethane (15 ml). After the addition was complete, the mixture was stirred at ambient temperature for 2.5 hours, then poured onto ice-water (500 ml). The aqueous layer was separated and washed with dichloromethane (3×100 ml), then the combined organic solutions were washed with saturated aqueous sodium hydrogen carbonate solution (2×100 ml) and water (100 ml), dried (CaCl2), and the solvents removed in vacua. The residue was distilled to give 2-bromo-1-[1-(3,4-dichlorophenyl)cyclobutyl]ethanone as a pale yellow oil (40.2 g), b.p. 156-164° C. at 0.8 mbar.
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