To a solution of 5-(2-oxo-2-(o-tolyl)ethyl)-5H-benzo[e]pyrido[3,2-b][1,4]diazepin-6(11H)-one (0.6 g, 1 eq.) in acetic acid (10 mL) was added ammonium acetate (2.7 g, 20 eq.). The reaction was stirred at 120° C. for 48 hours. The reaction was poured onto water (50 mL) and ethyl acetate (150 mL). The pH was adjusted to 9 by the addition of NaOH 1N. The phases were separated and washed with water (1×50 mL), brine (1×50 mL), dried over sodium sulfate, filtered and concentrated under reduced pressure. Purification by column chromatography (10% ethyl acetate in dichloromethane) gave the 2-(o-tolyl)-9H-benzo[f]imidazo[1,2-d]pyrido[2,3-b][1,4]diazepine (0.3 g, 53%). M.p.: 215-217° C.; 1H NMR (DMSO-d6) 400 MHz δ 8.60 (s, 1H), 8.18 (dd, JA=4.4 Hz, JB=1.2 Hz, 1H), 7.99 (dd, JA=8.0 Hz, JB=1.2 Hz, 1H), 7.91-7.85 (m, 2H), 7.82 (s, 1H), 7.34-7.20 (m, 5H), 7.14 (dd, JA=8.0 Hz, JB=4.8 Hz, 1H), 7.05 (t, J=8.4 Hz, 1H), 2.56 (s, 3H); LCMS: 325 [M+H].
