[C:1]1([C:7]2[S:11][C:10]([CH:12]=[O:13])=[CH:9][CH:8]=2)[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[OH:14]P([O-])(O)=O.[K+].[O-]Cl=O.[Na+].[OH-].[Na+]>C1COCC1.CC(O)(C)C.O>[C:1]1([C:7]2[S:11][C:10]([C:12]([OH:14])=[O:13])=[CH:9][CH:8]=2)[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=1The product of Step 3a (750 mg, 4 mmol) is dissolved in a mixture of THF, t-BuOH, and water (2:1:1, 60 mL). KH2PO4 (1.36 g, 10 mmol) is added followed by NaClO2 (900 mg, 10 mmol). The mixture is stirred at rt for 5 days. Aqueous NaOH (2M, 10 mL) is added, and a majority of the organic solvents are removed in vacuo yielding an aqueous suspension. This suspension is diluted with water and washed three times with CH2Cl2. The aqueous layer is acidified to pH<6 with 25% H2SO4 and the product is extracted three times with CH2Cl2. The combined organic washes are dried over Na2SO4, filtered and concentrated in vacuo to yield 5-phenylthiophene-2-carboxylic acid (417 mg, 51%). MS for C11H8O2S (ESI) (M−H)− m/z 203.
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