2,3-Dibromothiophene → 3-Bromo-2-(2-methoxy-ethyl)-thiophene
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Br[C:2]1[S:3][CH:4]=[CH:5][C:6]=1[Br:7].[Li]CCCC.[CH3:13][O:14][CH2:15][CH2:16]OS(C1C=CC(C)=CC=1)(=O)=O>C1COCC1>[Br:7][C:6]1[CH:5]=[CH:4][S:3][C:2]=1[CH2:16][CH2:15][O:14][CH3:13]Br[C:2]1[S:3][CH:4]=[CH:5][C:6]=1[Br:7].[Li]CCCC.[CH3:13][O:14][CH2:15][CH2:16]OS(C1C=CC(C)=CC=1)(=O)=O>C1COCC1>[Br:7][C:6]1[CH:5]=[CH:4][S:3][C:2]=1[CH2:16][CH2:15][O:14][CH3:13]To a solution of 2,3-dibromothiophene (12.6 g, 50 mmol) in THF abs. (125 mL) was added at −75° C. n-BuLi (1.6M/hexane, 31 mL) over 30 minutes. The reaction mixture was further stirred at −75° C. for 30 minutes, and p-toluenesulfonic acid-2-methoxyethylester (11.8 g, 50 mmol) was added dropwise over 1 h. The mixture stirred for 2 h without cooling, quenched with brine, and extracted with ether. The organics were washed, dried, and concentrated. The residue was chromatographed on silica gel using heptane/ethyl acetate as eluent to obtain 3-bromo-2-(2-methoxy-ethyl)-thiophene (1.8 g) as a colorless liquid. MS (EI): 221.1 (M)
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