Bromine → ethyl 4-bromo-3,5-dimethyl-1H-pyrrole-2-carboxylate

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To a solution of ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate (3.42 g, 20 mmol) in carbon tetrachloride (40 mL) was added a solution of bromine in carbon tetrachloride (10 mL) dropwise at 20° C. After the addition was complete, stirring was continued for 2 h. The reaction mixture was diluted with DCM, washed with aqueous NaHCO3 and water, and then dried over Na2SO4. Evaporation of solvent gave ethyl 4-bromo-3,5-dimethyl-1H-pyrrole-2-carboxylate as a solid (4.8 g), which was used in the next step without purification. 1H-NMR (CDCl3): δ 9.36 (1H, s), 4.30 (2H, q), 228 (3H, s), 2.26 (3H, s), 1.36 (3H, t). To a solution of ethyl 4-bromo-3,5-dimethyl-1H-pyrrole-2-carboxylate (2.4 g, 10 mmol) in DMF (25 mL) was added tetrakis(triphenylphosphine)palladium (2.3 g, 1 mmol). After stirring 15 min, the reaction mixture was charged with 2-(trifluoromethyl)-benzeneboronic acid (2.4 g, 12.5 mmol) and sodium carbonate (in 5 mL of water). The reaction mixture was heated to reflux overnight with stirring. After cooling, the reaction mixture was then diluted with water and extracted with DCM. The combined extracts were washed with water and dried over Na2SO4. Evaporation of solvent gave a crude material, which was purified by chromatography on silica gel column eluting with EtOAc-hexane (1:1) to give the title compound (1.5 g). MS (ES): 312 (MH+);

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