4.4 At room temperature, 5-methoxyquinoline azide (Compound 2, 4.09 g, 23.3 mmol) was dissolved in a solvent mixture of 10% aqueous K2CO3 (60 mL) and dichloromethane (60 mL). Subsequently, p-toluenesulfonyl chloride (5.55 g, 29.1 mmol) was added in batches and the reaction mixture was stirred at the same temperature for 18 hours. Upon completion of the reaction, ether was added to precipitate the product, and the precipitate was collected by filtration and washed with ether. The resulting solid was dried in an oven at 65 °C for 2 h to give 5-methoxyquinolin-2(1H)-one as a pale yellow solid, yield: 2.651 g (65%). The product was characterized by 1H NMR (400 MHz, CDCl3) and 13C NMR (100 MHz, CDCl3) with the following data: 1H NMR δ 12.15 (br.s, 1H), 8.25 (d, J = 9.6 Hz, 1H), 7.45 (t, J = 8.4 Hz, 1H), 7.04 (d, J = 8.4 Hz, 1H) 6.67 (t, J = 9.2 Hz, 2H), 3.97 (s, 3H); 13C NMR δ 164.61, 156.09, 139.72, 135.74, 131.40, 119.67, 110.91, 108.66, 102.78, 55.73.
