[C:1]([C:4]1[S:8][C:7]([C:9]([OH:11])=[O:10])=[CH:6][CH:5]=1)(=[O:3])[CH3:2].[CH3:12][C:13](O)([CH3:15])[CH3:14].CCN=C=NCCCN(C)C.O>CC(N(C)C)=O.CN(C1C=CN=CC=1)C>[C:1]([C:4]1[S:8][C:7]([C:9]([O:11][C:13]([CH3:15])([CH3:14])[CH3:12])=[O:10])=[CH:6][CH:5]=1)(=[O:3])[CH3:2]A solution of 5-acetylthiophene-2-carboxylic acid (7 g, 41 mmol) in DMA (100 mL) was treated with 2-methyl-2-propanol (54 mL, 576 mmol), DMAP (3 g, 25 mmol), and EDCI (9.9 g, 51.5 mmol). The resulting mixture was stirred at 25° C. for 16 h. Water (200 mL) was added and the mixture was extracted with ethyl ether (350 mL). The organic phase was washed with 1 N HCl (100 mL), water (3×100 mL), saturated aqueous NaHCO3 (100 mL), and brine (100 mL); dried (Na2SO4); filtered; and evaporated to afford 6.7 g (72%) of the title compound as a tan solid. 1H NMR (300 MHz, DMSO-D6) δ ppm 1.53 (s, 9H) 2.58 (s, 3H) 7.75 (d, J=3.68 Hz, 1H) 7.92 (d, J=3.68 Hz, 1H); MS (DCI) 227 m/z (M+H)+.
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