C(N[CH:5]([CH3:7])[CH3:6])(C)C.[Li].[CH2:9]([CH:16]1N[C:19](=[O:21])[CH2:18][CH2:17]1)[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1.C(Br)CC.C(O)(=[O:28])C>C1COCC1>[CH2:9]([CH:16]1[O:28][C:19](=[O:21])[CH:18]([CH2:7][CH2:5][CH3:6])[CH2:17]1)[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1To a 2 M lithium diisopropylamine solution in THF of −78° C. is added 5-benzylpyrrolidin-2-one and the mixture is stirred for 1.5 hours at −78° C. Then 1-propyl bromide is added and the reaction is stirred for another 1.5 hours at −78° C. The reaction mixture is allowed to warm up to 0° C. before ice-cold water with acetic acid is added and subsequently extracted 3 times with dichloromethane. The dichloromethane is concentrated in vacuo and the residue is dissolved in dichloromethane, washed with saturated NaHCO3 and brine. Crude 5-benzyl-3-propyldihydrofuran-2(3H)-one is obtained after removal of the solvents in vacuo. The product is purified by column chromatography.
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