[CH3:1][CH2:2][O:3][C:4](/[CH:6]=[C:7](/[CH2:9]P(OCC)(OCC)=O)\[CH3:8])=[O:5].[Li]CCCC.[Cl:23][C:24]1[CH:31]=[C:30]([Cl:32])[CH:29]=[CH:28][C:25]=1[CH:26]=O>C1COCC1.CN1C(=O)N(C)CCC1>[CH2:2]([O:3][C:4](=[O:5])[CH:6]=[C:7]([CH3:8])[CH:9]=[CH:26][C:25]1[CH:28]=[CH:29][C:30]([Cl:32])=[CH:31][C:24]=1[Cl:23])[CH3:1]Triethyl 3-methyl-4-phosphonocrotonate (34.24 g, 0.129 mol, 1.3 eq) was dissolved in THF/DMPU (100 mL/200 mL) and the mixture was cooled to −78° C. BuLi (51.8 mL of a 2.5M solution in hexanes, 1.3 eq) was added dropwise. The mixture was stirred for 20 min and then a solution of 2,4-dichlorobenzaldehyde (17.6 g, 0.1 mol) in THF/DMPU (20 mL/40 mL) was added dropwise. The resulting mixture was stirred for 1 hour and then allowed to warm to room temperature. NH4Cl(sat) was added and the mixture extracted with EtOAc. The organic layers were washed with, water, brine, and dried (MgSO4). Removal of solvent under reduced pressure followed by silica gel chromatography (0-1-2-3% EtOAc in hexanes) gave 23.3 g of 5-(2,4-dichlorophenyl)-3-methylpenta-2,4-dienoic acid ethyl ester.
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