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Step 1. 5-formyl-2-thiophenecarboxylic acid (2.34 g, 15 mmol) was dissolved in DMF (25 ml) with sodium carbonate (5.57 g, 52.5 mmol) at 25 °C and iodomethane (1.15 ml, 18 mmol) was added slowly. The reaction mixture was stirred at room temperature for 20 h before the reaction was terminated by addition of water and saturated aqueous NH4Cl solution. The reaction mixture was filtered to collect the solid precipitate to give the crude methyl 5-formylthiophene-2-carboxylate. The filtrate was extracted with EtOAc (3 x 30 ml), the organic phases were combined and washed sequentially with water and brine, dried over anhydrous Na2SO4 and concentrated under reduced pressure. The crude product was purified by fast column chromatography and combined with the previously collected solids to give the final methyl 5-formylthiophene-2-carboxylate as a white solid (1.60 g, 62% yield).ESI-MS (m/z): 171.2 (M+H+).