P(Cl)(Cl)(Cl)=O.[Cl:6][C:7]([Cl:23])([C:19]([F:22])([F:21])[F:20])[CH:8](O)[CH2:9][C:10]([CH3:17])([CH3:16])[CH2:11][C:12]([O:14][CH3:15])=[O:13].O>N1C=C(C)C=C(C)C=1>[Cl:6][C:7]([Cl:23])([C:19]([F:20])([F:21])[F:22])[CH:8]=[CH:9][C:10]([CH3:16])([CH3:17])[CH2:11][C:12]([O:14][CH3:15])=[O:13]Phosphorus oxychloride (10 cm3) was added dropwise to a stirred solution of methyl 6,6-dichloro-3,3-dimethyl-5-hydroxy-7,7,7-trifluoroheptanoate (5.49 g) in 3,5-lutidine (50 cm3) maintained at 0° C. The resultant mixture was heated at 100° C. for 30 minutes, and then cooled to the ambient temperature under a nitrogen atmosphere, and poured into a stirred mixture of ice and water (300 cm3). The mixture was extracted with ethyl acetate (2×150 cm3), diethyl ether (3×150 cm3) and finally with ethyl acetate (150 cm3). The volume of the combined extracts was reduced to about 400 cm3 by evaporation of some of the solvents under reduced pressure, and then washed with dilute (3.5M) hydrochloric acid. The aqueous washings were extracted with diethyl ether (3×50 cm3) and the extracts combined with the organic phase. After washing the combined organic phase with brine and drying over anhydrous magnesium sulphate, the solvents were removed by evapoation under reduced pressure and the residual oil purified by Kugelrohr distillation (128° C./1 mm Hg) to give methyl 6,6-dichloro-3,3-dimethyl-7,7,7-trifluorohept-4-enoate as a pale yellow oil (2.86 g, 52% yield), together with a quantity of the allylically rearranged isomer methyl 4,6-dichloro-3,3-dimethyl-7,7,7-trifluorohept-5-enoate.
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