C[O:2][C:3]([C:5]1[S:6][CH:7]=[C:8]([CH2:11][O:12]C(=O)C)[C:9]=1[Cl:10])=[O:4].[OH-].[Na+]>O1CCOCC1.O>[C:3]([C:5]1[S:6][CH:7]=[C:8]([CH2:11][OH:12])[C:9]=1[Cl:10])([OH:4])=[O:2]To a solution of 2-methoxycarbonyl-3-chloro-4-(acetoxymethyl)thiophene (83 g, 0.33 mol) in 1,4-dioxane (350 mL) was added a solution of sodium hydroxide (26.5 g, 0.66 mol) in water (200 mL) and the mixture stirred at ambient temperature. After 1 hour the dioxane was removed in vacuo and the aqueous solution washed with ethyl acetate (2×1 00 mL). The aqueous layer was brought to pH 2 by addition of concentrated HCl, then extracted with n-butanol (4×200 mL). The combined extracts were concentrated and the resulting solid dried in vacuo to afford 63 g (90% yield) of 2-carboxy-3-chloro-4-(hydroxymethyl)thiophene as a tan powder; NMR (DMSO-d6) 7.7 (s, 1), 4.4 (s, 2) ppm.
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