[C:1]([C:4]1[CH:9]=[CH:8][C:7]([C:10]2[CH:15]=[CH:14][C:13]([F:16])=[CH:12][C:11]=2[F:17])=[CH:6][CH:5]=1)(=O)[CH3:2].[CH2:18]([O:20][C:21]#[C:22][Mg]Br)[CH3:19].C([O:27]C#C)C.C([Mg]Br)C>CCOCC.C1COCC1>[CH2:18]([O:20][C:21](=[O:27])[CH:22]=[C:1]([C:4]1[CH:9]=[CH:8][C:7]([C:10]2[CH:15]=[CH:14][C:13]([F:16])=[CH:12][C:11]=2[F:17])=[CH:6][CH:5]=1)[CH3:2])[CH3:19]A solution of 23.2 g. of 4-acetyl-2',4'-difluorobiphenyl in 50 ml. of THF and 50 ml. of ether is added slowly dropwise to a solution of 17.5 g. of ethoxyethinylmagnesium bromide in 200 ml. of ether, prepared by reacting ethoxyacetylene with ethyl magnesium bromide. The mixture is stirred for 1 hour at 20°. The reaction product is hydrolyzed with ice water/ammonium chloride and extracted with ether. The combined ether extracts are dried over MgSO4 and evaporated. Residual 1-ethoxy-3-(2',4'-difluoro-4-biphenylyl)-butyn-3-ol is dissolved in 200 ml. of 95% ethanol and 0.05 g. of solid CO2 is added to the solution and the mixture is left to stand for 12 hours at 20°. The customary work up gives 3-(2',4'-difluoro-4-biphenylyl)-2-butenoic acid ethyl ester, m.p. 54°-56°.
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