Cesium carbonate → methyl 5-(1H-pyrazol-4-yl)thiophene-3-carboxylate

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5-Bromo-thiophene-3-carboxylic acid methyl ester (6 g, 27 mmol) was dissolved in a mixture of DME (75 mL), IMS (25 mL) and water (12.5 mL). Caesium carbonate (13.2 g, 40 mmol) and 4-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-pyrazole-1-carboxylic acid tert-butyl ester (9.2 g, 31 mmol) were added and the mixture stirred under argon. Palladium tetrakis-(triphenylphosphine) (3.1 g, 2.7 mmol) was then added and the mixture heated at 110° C. for 6 hours. The mixture was allowed to cool to room temperature and then diluted with water. The product was extracted into DCM and washed with brine, then dried over sodium sulphate, filtered and the solvent removed by evaporation under vacuum. The residue was triturated with diethyl ether to give the title compound as a pale yellow solid (3.01 g). LCMS m/z 209.1 [M+H]+. R.T.=3.72 min (Analytical Method 4). 1H NMR (400 MHz, d6-DMSO): δ 8.2 (s, 1H), 8.15 (s, 1H), 7.85 (s, 1H), 7.5 (s, 1H), 3.8 (s, 3H).

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