Acetic Anhydride → ethyl 5-cyano-4-(nitrophenyl)-1H-pyrrole-3-carboxylate

To a solution of ethyl 5-formyl-4-(nitrophenyl)-1H-pyrrole-3-carboxylate (24.55 g, 85.17 mmol) in pyridine (400 mL) was added hydroxylamine hydrochloride (6.51 g, 93.7 mmol). The solution was stirred at rt for 2 h, and then acetic anhydride (17.68 mL, 187.4 mmol) was added. The solution was heated (80° C.) for 17 h and then cooled to rt. The reaction mixture was partially concentrated in vacuo and then diluted with ethyl acetate (300 mL) and water (300 mL). The layers were separated and the aqueous layer was back extracted with ethyl acetate (2×100 mL). The combined organic layers were dried over sodium sulfate and concentrated to dryness. The crude material was then triturated with dichloromethane-diethyl ether (1:1 v/v, 300 mL). The solid was collected, washed with diethyl ether (150 mL), and dried under vacuum to afford the desired product (18.94 g, 78%). 1H-NMR (300 MHz, DMSO-d6) 13.24 (br s, 1H), 8.25-8.32 (m, 2H), 7.92 (s, 1H), 7.69-7.76 (m, 2H), 4.13 (q, J=7.2 Hz, 2H), 1.16 (t, J=7.0 Hz, 3H); HPLC RT (Method A) 2.97 min; TLC Rf=0.20 (95:5 v/v CH2Cl2-EtOAc).