4H-Thiopheno[3,2-b]pyrrole-5-carboxylic acid (3.0 g, 17.9 mmol) was dissolved in anhydrous methanol (50.0 mL) and the solution was cooled to 0°C. A hexane solution of trimethylsilylated diazomethane (45.0 mL, 2 M) was added slowly and dropwise with stirring, keeping the yellow color of the reaction solution from fading. The reaction continued to be stirred for 10 minutes before acetic acid (5.0 mL) was added to quench the excess trimethylsilylated diazomethane. Subsequently, the solvent was removed by a stream of nitrogen and the residue was purified by silica gel column chromatography (elution gradient: 5%-40% ethyl acetate in heptane solution, 30 min) to afford methyl 4H-thieno[3,2-b]pyrrole-5-carboxylate (2.8 g, 86% yield). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ 3.90 (s, 3H), 6.95 (dd, J = 5.32, 0.78 Hz, 1H), 7.13 (dd, J = 1.88, 0.76 Hz, 1H), 7.33 (d, J = 5.37 Hz, 1H), 9.02 (br.s, 1H).
![4H-THIENO[3,2-B]PYRROLE-5-CARBOXYLIC ACID](/CAS/GIF/39793-31-2.gif)
