Example 4: Preparation of Compound 4 (7-nitro-1H-indole); Compound 3 (7-nitroindole-2-carboxylic acid, 1.63 g, 7.91 mmol) was dissolved in quinoline (13 mL) followed by addition of copper oxide (CuO, 0.19 g). The reaction mixture was stirred and heated to 194 °C. During heating, gas was observed to escape. After 2 hours of reaction, gas production stopped and the completion of the reaction was confirmed by thin layer chromatography (TLC). The reaction solution was slowly poured into a dilute hydrochloric acid solution prepared from concentrated hydrochloric acid (21.3 mL) and cold water (42.6 mL) and stirred to produce a black precipitate. The reaction mixture was filtered to separate the black precipitate and the filtrate was extracted with ether. The organic phases were combined and washed sequentially with saturated sodium bicarbonate (NaHCO3) solution and deionized water. The organic layer was dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated to give a yellow solid. The solid was recrystallized in ethanol (EtOH) to give an acicular light yellow solid, compound 4 (7-nitro-1H-indole, 0.87 g, 69% yield). Melting point 96-97 °C (literature value 95-96 °C); 1H NMR (200 MHz, CDCl3) δ 6.63 (dd, J = 2.2, 1.0 Hz, 1H, ArH), 7.08-7.18 (m, 1H, ArH), 7.32 (t, J = 3.0 Hz, 1H, ArH), 7.90 (d, J = 7.8 Hz, 1H, ArH), 8.08 (d, J = 8.1 Hz, 1H, ArH), 9.88 (s, 1H, NH); 13C NMR (50 MHz, acetone-d6) δ 103.7, 118.9, 119.2, 128.4, 129.1, 129.3, 132.9, 133.5; mass spectrometry (EI) m/z 162 (M+, 100%), 116 (M-46 ), 116 (M-46, 87%), 104 (M-58, 41%), 89 (M-73, 53%).
