C[Si](C)(C)[C:3]#[C:4][C:5]1[S:9][C:8]([C:10]([O:12]CC)=[O:11])=[CH:7][CH:6]=1.[Li+].[OH-].O.Cl>C1COCC1>[C:4]([C:5]1[S:9][C:8]([C:10]([OH:12])=[O:11])=[CH:7][CH:6]=1)#[CH:3]To a solution of ethyl 5-(2-trimethylsilyl-ethyn-1-yl)-thiophene-2-carboxylate prepared above (529 mg, 2.10 mmol) in THF (20 mL), 1N aq. LiOH (7.0 mL, 7.0 mmol) was added. After the mixture was stirred at 40° C. overnight, it was poured into water. The aqueous solution was acidified with 1N HCl to pH 1. The product was extracted with EtOAc. The EtOAc solution was washed with brine, dried over MgSO4, concentrated in vacuo to give 5-ethynyl-thiophene-2-carboxylic acid (316 mg). MS 153 (M+H).
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