Synthesis of Intermediates 7a–ab. Reagents and conditions: (a) alkyl bromide, TEA, MeOH, reflux, 2 h; (b) fuming nitric acid, AcOH, 25–45 °C, 1 h; (c) POCl3, DMA, reflux, 2 h; (d) Fe, AcOH, MeOH, reflux; (e) appropriate amines, TEA, EtOH, reflux, 48 h; (f) NaNO2, AcOH, H2O, 10 °C, 1 h.