[CH3:1][O:2][C:3]([C:5]1[S:6][C:7]([CH:11](OCC)[O:12]CC)=[CH:8][C:9]=1[CH3:10])=[O:4].C(O)=O>O1CCOCC1>[CH3:1][O:2][C:3]([C:5]1[S:6][C:7]([CH:11]=[O:12])=[CH:8][C:9]=1[CH3:10])=[O:4]A solution of 5-diethoxymethyl-3-methyl-thiophene-2-carboxylic acid methyl ester (4.41 g, 17.1 mmol) in dioxane (20 ml) was cooled to 0° C. (ice bath). 88% formic acid (40 ml) was added in one portion and the mixture was stirred at 0° C. for 5 min and then at rt for 30 min. The mixture was concentrated under reduced pressure to afford the desired product which was not further purified (3.2 g, 100% yield).
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