General procedure for the synthesis of 1H-cinnolin-4-one from o-aminoacetophenone:
Preparation of Intermediate 1: 1,4-dihydro-4-quinolinone: An aqueous solution (10 mL) of sodium nitrite (4.0 g, 59 mmol) was slowly added dropwise over 20 min to a stirred mixture of 2-aminoacetophenone (5.0 g, 37.03 mmol) with concentrated hydrochloric acid (31 mL) under ice bath cooling conditions. The reaction mixture was continued to be stirred at the same temperature for 2 hours, then brought to room temperature and stirred overnight. After completion of the reaction, the mixture was concentrated under reduced pressure. The residue was neutralized with aqueous sodium acetate and then subjected to post-extraction treatment (ethyl acetate/brine) to give the final 1H-cinnolin-4-one (1.25 g, 23% yield).
1H-NMR (δ ppm, DMSO-d6, 300 MHz): 13.48 (br.s, 1H); 8.01 (d, J = 8.1 Hz, 1H); 7.82-7.73 (m, 2H); 7.57 (d, J = 8.1 Hz, 1H); 7.41 (t, J = 7.8 Hz, 1H).
