1. Oxidation: 1,8-Naphthalenedicarboxylic anhydride (2.31 g, 15.0 mmol) was dissolved in acetic acid (60 mL) and sodium dichromate (11.17 g, 40.0 mmol) was added under stirring conditions at room temperature. The suspension was heated to 75 °C and the reaction was carried out for 8 hours. After the reaction was completed, cold water was added to precipitate the product, which was filtered and washed with water to obtain white 1,8-naphthalenedicarboxylic anhydride (2.6 g, 80%, melting point 266-268 °C).
2. Bromination: 1,8-naphthalenedicarboxylic anhydride (1.98 g, 10.0 mmol) was dissolved in aqueous KOH (2.8 g KOH in 12 mL of water), cooled, and bromine was added dropwise. The reaction mixture was heated to 60 °C and kept for 6 h, then acidified with HCl solution. The crude product was obtained by filtration, the solid was dissolved by heating with 5% NaOH solution, filtered and neutralized with HCl solution, filtered again and washed with cold water, and dried to obtain yellow 4-bromo-1,8-naphthalenedicarboxylic anhydride (2.05 g, 82%, melting point 117-119 °C).
3. Condensation: 4-bromo-1,8-naphthalenedicarboxylic anhydride (2.00 g, 5.0 mmol) was refluxed with o-phenylenediamine (0.618 g, 5.0 mmol) in THF for 6 hours. After completion of the reaction (monitored by TLC), the reaction mixture was cooled, filtered and washed with THF to afford brown 3-bromo-benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (2.51 g, 63%, melting point 190-192 °C).
Product characterization: 1H NMR (CDCl3 + TFA) δ 8.90 (dd, J=8.48, 0.68 Hz, 1H, ArH), 8.79 (dd, J=7.36, 0.84 Hz, 1H, ArH), 8.53 (d, J=7.92 Hz, 1H, ArH), 8.24 (d, J=7.92 Hz, 1H, ArH), 8.04 (dd, J=7.92 Hz, 1H, ArH), 8.04 (dd, J=7.92 Hz, 1H, ArH), 8.05 (dd, J=7.92 Hz, 1H, ArH). 8.04 (dd, J=8.48, 7.48 Hz, 1H, ArH), 7.74 (m, 3H, ArH), 7.56 (m, 1H, ArH); 13C NMR (CDCl3 + TFA) δ 165.76, 136.55, 134.50, 134.42, 133.44, 131.92, 131.75, 131.68, 131.15, 130.90, 129.30, 128.64, 128.20, 127.26, 124.97, 121.02, 119.98; EIMS m/z: 350 (M+ + 1). Calculated elemental analysis (C18H9BrN2O): C, 61.91; H, 2.60; N, 8.08. Measured values: C, 61.76; H, 2.81; N, 8.45.
