Preparation of 6,7-dihydro-5H-quinolin-8-one: 8-hydroxy-5,6,7,8-tetrahydroquinoline (13.96 g, 93.6 mmol) was dissolved in anhydrous dichloromethane (400 mL) under stirring conditions. Subsequently, activated manganese dioxide (85% pure, 82.22 g, 804 mmol) was added to this solution. The resulting non-homogeneous mixture was stirred for 18 hours. Upon completion of the reaction, the black slurry was filtered through a diatomaceous earth filter cake and the cake was washed with dichloromethane (3 x 50 mL). The washes were combined and concentrated to afford 11.27 g (82% yield) of the target product, 6,7-dihydro-5H-quinolin-8-one, as a light yellow solid, which could be used in subsequent reactions without further purification. The structure of the product was characterized by 1H NMR (CDCl3) δ 2.17-2.25 (m, 2H), 2.82 (t, 2H, J = 7 Hz), 3.04 (t, 2H, J = 6 Hz), 7.37 (dd, 1H, J = 9,6 Hz), 7.66 (dd, 1H, J = 9,1 Hz), 8.71 (dd, 1H, J = 6,1 Hz); 13C NMR (CDCl3) δ 22.2, 28.6, 39.2, 126.6, 137.3, 140.5, 147.6, 148.6, 196.5 confirmed.ES-MS m/z 148 (M + H) further validated the product structure.
