C(OCC)(=O)CC(OCC)=O.[H-].[Na+].C1(CBr)CC1.[CH2:19]([O:21][C:22](=[O:33])[CH:23]([CH2:29][CH2:30][CH:31]=[CH2:32])[C:24]([O:26][CH2:27][CH3:28])=[O:25])[CH3:20]>C1COCC1>[CH2:19]([O:21][C:22](=[O:33])[CH:23]([CH2:29][CH:30]1[CH2:32][CH2:31]1)[C:24]([O:26][CH2:27][CH3:28])=[O:25])[CH3:20]To an ice-cooled solution of diethyl malonate (3.0 g, 18.7 mmol) in THF (30 mL) was added, portionwise over 15 min, sodium hydride (0.824 g, 60% in oil, 20.6 mmol). The mixture was stirred at RT for 30 min, and then cooled in an ice bath. Cyclopropylmethyl bromide (2.36 mL, 24.3 mmol) was added and the reaction mixture stirred at RT for 1 h and then refluxed for 6 h. The cooled mixture was concentrated in vacuo, the residue was partitioned between diethyl ether and dilute aqueous NH4Cl; and the aqueous phase was extracted with diethyl ether. The combined organic phases were washed with brine, then dried (Na2SO4) and concentrated in vacuo. The resulting residue was purified by column chromatography (Si-PCC, gradient 2-8% EtOAc in cyclohexane) affording a mixture of the title compound and 2-but-3-enylmalonic acid diethyl ester (3.24 g, 10:1 ratio respectively). This mixture was dissolved in DCM (150 mL) and a solution of mCPBA (0.77 g, 4.46 mmol) in DCM (5 mL) added. The reaction mixture was stirred at RT for 16 h, and then washed with a saturated solution of NaHCO3, dried (Na2SO4) and concentrated in vacuo. The resulting residue was purified by column chromatography (Si-PCC, gradient 2-8% EtOAc in cyclohexane) affording the title compound as a colourless oil (2.68 g, 67%). 1H NMR (CDCl3, 300 MHz): δ 4.20 (4H, q, J=7.1 Hz), 3.44 (1H, t, J=7.5 Hz), 1.81 (2H, t, J=7.3 Hz), 1.27 (6H, t, J=7.1 Hz), 0.80-0.67 (1H, m), 0.48-0.42 (2H, m), 0.12-0.07 (2H, m).
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