[CH3:1][C:2](C)([O-])[CH3:3].[K+].[OH:7][C:8]1[CH:12]=[C:11]([CH3:13])[O:10][C:9]=1[C:14]([O:16][CH2:17][CH3:18])=[O:15].BrC(C)C.O>CS(C)=O>[CH3:13][C:11]1[O:10][C:9]([C:14]([O:16][CH2:17][CH3:18])=[O:15])=[C:8]([O:7][CH:2]([CH3:3])[CH3:1])[CH:12]=1A solution of 1.6 g (14.3 mmol, 1.2 equiv) of potassium tert-butoxide in 11 mL of dimethyl sulfoxide is added to a solution of 2.0 g (11.8 mmol) of ethyl 3-hydroxy-5-methyl-2-furancarboxylate (Takei, H. and Mukaiyama, T., Bull. Soc. Chem. Jpn., 43, 3607 (1970)) in 40 mL of dimethyl sulfoxide under a nitrogen atmosphere. The resulting solution is stirred at room temperature for 1 hour and treated with 5.9 g (47.9 mmol, 4.1 equiv) of 2-bromopropane. The reaction is stirred at room temperature for 7.5 hours under nitrogen and poured onto 100 mL of water. The aqueous solution is extracted with ethyl acetate (4x). The combined extracts are washed with water (2x) and saturated aqueous sodium chloride, dried over sodium sulfate and concentrated in vacuo to give 1.7 g (2.5 g theo., 68%) of ethyl 5-methyl-3-isopropoxy-2-furancarboxylate as a pale, yellow oil.
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