[CH3:1][O:2][C:3](=[O:18])[CH:4]([C:9]([CH3:17])([C:11]1[O:12][C:13]([CH3:16])=[CH:14][CH:15]=1)[CH3:10])C(OC)=O.[Li+].[Cl-].O>CS(C)=O>[CH3:1][O:2][C:3](=[O:18])[CH2:4][C:9]([CH3:10])([C:11]1[O:12][C:13]([CH3:16])=[CH:14][CH:15]=1)[CH3:17]Step C To a solution of 2-[1-methyl-1-(5-methyl-furan-2-yl)-ethyl]-malonic acid dimethyl ester (2.5 g, 9.8 mmol) in DMSO (30 mL) was added LiCl (1 g, 23.7 mmol) and H2O (0.17 mL, 9.8 mmol). The reaction mixture was heated at 170° C. for 3 h, then poured into a ice-water, extracted with ethyl acetate. The organic layer were separated, washed with water, brine, dried over MgSO4, and concentrated. The residue was purified by chromatography (EtOAc:hexanes=1:20, 1:20) to give 3-methyl-3-(5-methyl-furan-2-yl)-butyric acid methyl ester as a colorless oil (1.5 g, 78%).
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