P(N(C)C)(N(C)C)N(C)C.[C:11](Br)(Br)([F:13])[F:12].[CH3:16][O:17][C:18]1[CH:32]=[CH:31][C:21]([CH2:22][N:23]2[C:27](=[O:28])[CH2:26][CH:25]([CH:29]=O)[CH2:24]2)=[CH:20][CH:19]=1.[PH4+]>C1COCC1>[F:12][C:11]([F:13])=[CH:29][CH:25]1[CH2:24][N:23]([CH2:22][C:21]2[CH:31]=[CH:32][C:18]([O:17][CH3:16])=[CH:19][CH:20]=2)[C:27](=[O:28])[CH2:26]1
In a three necked flask under argon, (Me2N)3P (11.53 ml, 0.063 mol) is added to a solution of CF2Br2 (6.6 g, 0.031 mol) in THF (30 ml) at −78° C. (appearance of a white precipitate) and warmed to room temperature. A solution of the 1-(4-methoxy-benzyl)-5-oxo-pyrrolidine-3-carbaldehyde a3 (3.7 g, 0.016 mol) in THF (30 ml) is added dropwise to the pre-formed phosphonium salt. After 1 h, the reaction mixture is filtered through celite and concentrated in vacuo. The reaction mixture is diluted with hexane, washed with brine, dried over MgSO4 and concentrated in vacuo to afford the crude olefin which is purified by column chromatography on silicagel (CH2Cl2/MeOH: 99/01 (v/v)) to afford 2.45 g of the difluorovinyl derivative a4 (58%).
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