General procedure for the synthesis of methyl 5-cyano-1H-pyrrole-2-carboxylate from methyl 5-formyl-1H-pyrrole-2-carboxylate: NH2OH-HCl (0.58 g, 8.4 mmol) and NaOAc (0.63 g, 7.6 mmol) were added to an 5-formyl-1H-pyrrole-2-carboxylic acid methyl ester (1.14 g, 7.6 mmol) in an anhydrous MeOH solution (8 mL). The reaction mixture was heated at reflux temperature for 1 hour. Upon completion of the reaction, the reaction was quenched with aqueous NaHCO3 and the aqueous layer was extracted three times with CH2Cl2. The organic layers were combined, dried with anhydrous MgSO4 and concentrated in vacuum to give the corresponding aldoxime (1.11 g, 87% yield). The crude aldoxime (5.8 g, 34 mmol) was dissolved in anhydrous N,N-dimethylformamide (DMF, 28 mL) and POCl3 (8.4 g, 55 mmol) was added dropwise to the solution at -20 °C. After stirring for 30 minutes at -20°C, the solution was brought to room temperature and continued to stir for 2 hours. After completion of the reaction, the reaction was quenched with water and the aqueous layer was extracted three times with CH2Cl2. The organic layers were combined, washed five times with water, dried over anhydrous MgSO4, and concentrated in vacuum to afford methyl 5-cyano-1H-pyrrole-2-carboxylate (4.2 g, 71% yield) as a colorless solid (mp = 173.7-174.8 °C) with an Rf of 0.23 (hexane/ethyl acetate = 3:1).1H NMR (400 MHz, CDCl3) δ 9.92 ( br, 1H), 6.89 (dd, J = 3.9,2.5 Hz, 1H), 6.84 (dd, J = 4.0,2.6 Hz, 1H), 3.94 (s, 3H); 13C NMR (101 MHz, CDCl3) δ160.9,126.7,120.1,115.2,112.8,105.7,52.7; HRMS (EI) calculated value C7H6N2O2: [M]+, 150.0429. measured value: m/z 150.0430.
