C(NC(C)C)(C)C.C([Li])CCC.CCCCCC.[S:19]1[CH:23]=[CH:22][CH:21]=[C:20]1[C:24]([OH:26])=[O:25].Cl[C:28]([O:30][CH2:31][CH3:32])=[O:29].C([O-])(O)=O.[Na+]>C1COCC1>[C:28]([C:23]1[S:19][C:20]([C:24]([OH:26])=[O:25])=[CH:21][CH:22]=1)([O:30][CH2:31][CH3:32])=[O:29]To a solution of diisopropylamine (3.6 mL, 25.75 mmol) in 10 mL of THF at -78° C. under argon was added a 1.6M solution of n-butyllithium in hexane (16.1 mL, 25.75 mmol). The mixture was stirred for 15 min, and a solution of 2-thiophenecarboxylic acid 34 (1.5 g, 11.705 mmol) (2-thiophenecarboxylic acid 34 is readily available from Aldrich) in 5 mL of THF was added slowly. The mixture was stirred for 15 min, and ethyl chloroformate (2.7 mL, 28.33 mmol) was added. The mixture was stirred for 30 min at -78° C., and warmed to 0° C. for another 30 min. The reaction mixture was poured into saturated aqueous NaHCO3, and washed with 80% ethyl acetate/hexane. The aqueous layer was acidified with acetic acid and extracted with 80% ethyl acetate/hexane. The combined organic layers were dried over anhydrous MgSO4, filtered, and concentrated to afford a yellow solid. Flash chromatography yielded the desired acid 35 (1.76 g, 75%) as a white solid: m.p. >300° C. The structure of the product was also confirmed using IR, 1H NMR and mass spectroscopy.
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