Ethanol → 1-(Thieno[2,3-b]pyridin-5-yl)ethanone

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To a vigorously stirred mixture of 2-nitrothiophene (Aldrich, 12.9 g, 0.1 mol) in concentrated HCl (Aldrich, 36.5%, 195 mL) was carefully added tin (Aldrich, 100 mesh, 25 g, 0.21 mol) at 20-30° C. After most of tin metal had been dissolved, EtOH (Aldrich, 70 mL) and ZnCl2 (Aldrich, 6.0 g, 0.044 mol) were added and the mixture was then heated to 75° C. for 1 h. The brown solution was cooled down to ambient temperature and 4,4-dimethoxybutan-2-one (Aldrich, 39.6 g, 0.3 mol) in EtOH (50 mL) was added. The reaction mixture was stirred at 70° C. for 10 h. The cooled brown reaction mixture was poured into NaOH aqueous solution (50%. 160 mL) and extrated with EtOAc (3×500 mL). The combined extracts were washed with brine (2×50 mL) and concentrated. The residue was purified with chromatography (SiO2, EtOAc/hexane, v. 20/80, Rf=0.30) to give the title compound (4.20 g, yield, 23%). 1H NMR (300 MHz, CDCl3) δ ppm 2.72 (s, 3 H), 7.38 (d, J=6.10 Hz, 1 H), 7.64 (d, J=6.10 Hz, 1 H), 8.63 (d, J=2.03 Hz, 1 H), 9.14 (d, J=2.03 Hz, 1 H); MS (DCI/NH3) M/z 178 (M+1)+, 195 (M+NH4).

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