[CH3:1][O:2][C:3]([C:5]1[S:6][C:7]([CH:14](OCC)[O:15]CC)=[CH:8][C:9]=1[C:10]([CH3:13])([CH3:12])[CH3:11])=[O:4].C(O)=O>O1CCOCC1>[CH3:1][O:2][C:3]([C:5]1[S:6][C:7]([CH:14]=[O:15])=[CH:8][C:9]=1[C:10]([CH3:11])([CH3:12])[CH3:13])=[O:4]A solution of 5-diethoxymethyl-3-tert-butyl-thiophene-2-carboxylic acid methyl ester (1.84 g, 6.1 mmol) in dioxane (10 ml) was cooled to 0° C. (ice bath). 88% formic acid (20 ml) was added in one portion and the mixture was stirred at 0° C. for 5 min and then at rt for 2 h. The mixture was concentrated under reduced pressure to afford the desired product which was not further purified (1.57 g, 100% yield).
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