[OH:1][CH:2]([CH3:11])/[CH:3]=[C:4](\[CH3:10])/[C:5]([O:7][CH2:8][CH3:9])=[O:6].[CH2:12]([O:14][P:15](Cl)([O:17][CH2:18][CH3:19])=[O:16])[CH3:13]>N1C=CC=CC=1>[CH2:12]([O:14][P:15]([O:17][CH2:18][CH3:19])([O:1][CH:2]([CH3:11])/[CH:3]=[C:4](\[CH3:10])/[C:5]([O:7][CH2:8][CH3:9])=[O:6])=[O:16])[CH3:13]29 (rac-Ethyl (2E)-4-hydroxy-2-methylpent-2-enoate) (0.99 g, 6.0 mmol) is dissolved in pyridine (1.6 ml) and cooled to 0° C. Diethylchlorophosphate (1.1 ml, 7.5 mmol) is added under stirring over 20 min at ≧3° C. After 4.5 hours of additional stirring at 0° C., the reaction mixture is quenched with 1 M H2SO4 (100 ml) and extracted with tBuOMe (300 ml) successively. The organic phase is washed with brine (50 ml), saturated NaHCO3 (50 ml) and brine (50 ml). The organic phase is dried with Na2SO4 and evaporated under reduced pressure at 40° C. The residue is purified by flash chromatography (AcOiPr:heptane fraction 50:50 to 60:40) to yield 17 (rac-Ethyl (2E)-4-(diethoxyphosphinyloxy)-2-methylpent-2-enoate) (1.56 g, 88%) as a yellowish oil.
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