[Br:1][C:2]([Br:13])([Br:12])[CH2:3][C:4]1(Cl)[C:7]([CH3:9])([CH3:8])[CH2:6][C:5]1=[O:10].[ClH:14]>C(O)C>[Br:1][C:2]([Br:13])([Br:12])[CH2:3][CH:4]1[C:7]([CH3:9])([CH3:8])[CH:6]([Cl:14])[C:5]1=[O:10]22.8 g (0.054 mole) of 2-(2',2',2'-tribromoethyl)-2-chloro-3,3-dimethylcyclobutan-1-on is dissolved in 220 ml of absolute ethanol saturated with hydrogen chloride and the solution is stirred for 5 hours at 80° C. Then solvent is evaporated until the volume of the reaction mixture is reduced to one third of the starting volume and, after addition of water, the mixture is extracted with ether. The etheral extract is washed at first with saturated sodium chloride solution and subsequently with sodium bicarbonate solution and thereafter dried over sodium sulphate. The residue obtained after evaporation of the ether is purified by chromatography on silica gel using toluene as eluent. After combination of the pure fractions and evaporation of the solvent there is obtained 17.1 g (75% of theory) of 2-(2',2',2'-tribromoethyl)-3,3-dimethyl-4-chloro-cyclobutane-1-one, melting point 87°-89° C.
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