Ethyl 7-nitroindole-2-carboxylate

292853-66-8

6960-46-9

Example 2: Synthesis of ethyl 7-nitro-1H-indole-2-carboxylate In a 250 mL three-neck flask, dry Compounds 1a and 1b (12.00 g, 47.76 mmol) and polyphosphoric acid (64.56 g, 191.05 mmol) were added. The mixture was heated to 70 °C with thorough stirring, followed by warming to 80 °C for 12 h of reaction. The reaction progress was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the viscous black reaction solution was slowly poured into cold water (400 g) while it was still hot and stirred until the polyphosphoric acid was completely hydrolyzed. At this point, the solution was black in color and a brown-black solid precipitated. The solid was collected by filtration and dried. The dried brown-black solid was extracted continuously for 12 h using Soxhlet extraction method with petroleum ether (boiling point 60-90 °C) as solvent. After completion of extraction, the petroleum ether solution was concentrated to give a yellow solid. Further by ethanol recrystallization, needle-like yellow crystals were obtained, i.e., the target product ethyl 7-nitro-1H-indole-2-carboxylate (10.5 g, 94% yield). Product characterization: Melting point: 92-93°C (literature value: 91-93°C); 1H NMR (200 MHz, CDCl3) δ: 1.41 (t, J = 7.2 Hz, 3H, CH3), 4.42 (q, J = 7.2 Hz, 2H, CH2), 7.20 (t, J = 7.9 Hz, 1H, ArH), 7.28 (d, J = 2.1 Hz, 1H, ArH), 7.97 (d, J = 7.8 Hz, 1H , ArH), 8.21 (d, J = 8.0 Hz, 1H, ArH), 10.25 (s, 1H, NH). 13C NMR (50 MHz, CDCl3) δ: 14.8, 62.0, 109.7, 120.5, 122.6, 130.0, 130.6, 131.1, 131.3, 133.8, 161.1; MS (EI) m/z. MS (EI) m/z: 235 (M+1, 100%), 234 (M+, 69%), 189 (M-45, 38%).