[F:1][C:2]1[CH:3]=[C:4]([O:9][CH:10]2[CH2:12][CH2:11]2)[CH:5]=[C:6]([F:8])[CH:7]=1.O1CCCC1.C([Li])CCC.[CH2:23]([O:25][C:26](Cl)=[O:27])[CH3:24]>CCOCC.[Cl-].[Na+].O>[CH:10]1([O:9][C:4]2[CH:3]=[C:2]([F:1])[C:7]([C:26]([O:25][CH2:23][CH3:24])=[O:27])=[C:6]([F:8])[CH:5]=2)[CH2:12][CH2:11]1
To a 250 ml round bottom flask was added cyclopropyl 3,5-difluorophenyl ether (3.6 g, 21.2 mmol) and 60 ml tetrahydrofuran. n-Butyllithium (nBuLi) (2.5 M, 8.9 ml, 22.2 mmol) was added via a syringe at −78° C. The resulting solution was stirred at −78° C. for 20 minutes. Ethylchloroformate (3.05 ml, 31.7 mmol) was added by a syringe. The resulting solution was left stirring for 5 more minutes. The reaction mixture was diluted with 100 ml ether and 60 ml brine. The layers were separated, and the organic portion was dried over sodium sulfate, filtered and concentrated. The crude product was purified on silica gel column eluted with hexane to 1:9 ethyl acetate/hexane gradient solvent to give 4.5 g desired product as yellow liquid.
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