[S:1]1[CH:5]=[CH:4][CH:3]=[C:2]1[C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7].CN(C)CCN(C)C.[C:21](=O)=[O:22].CC(C)=O.C([Li])(C)(C)C>CCCCC.CN(C)C=O>[CH:21]([C:5]1[S:1][C:2]([C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7])=[CH:3][CH:4]=1)=[O:22]
A solution of t-butyl 2-thiophenecarboxylate (1.84 g, 10 mmol) and N,N,N',N'-tetramethylethylenediamine (1.74 g, 15 mmol) in anhydrous tatrahydrofuran was stirred in a nitrogen stream under cooling with dry ice/acetone, followed by the dropwise addition of a 1.7M solution (8.0 ml) of t-butyllithium (13.6 mmol) in pentane. The obtained mixture was stirred as such for about 50 minutes. Anhydrous dimethylformamide (15 ml) was gradually dropped into the resulting mixture to conduct a reaction. The dry ice/acetone was removed to raise the temperature of the mixture to room one. The resulting mixture was stirred for 40 minutes and poured into 300 ml of a diethyl ether/0.3 N HCl (3:1) mixture. The obtained mixture was stirred for a while. The organic layer was recovered, washed with a phosphate buffer solution having a pH of 7 and an aqueous solution of common salt, dehydrated and distilled to remove the solvent. The residue was purified by silica gel column chromatography (developer: n-hexane/ethyl acetate=8:1) to give t-butyl 5-formyl-2-thiophenecarboxylate. yield: 1.7 g
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