Scheme 1

Synthesis of compounds 8a, 8b, and 8c. Reagents and conditions: (i) 1-fluoro-2-nitrobenzene, NaH, THF, rt, 20 h, 60%; (ii) SnCl₂, EtOH, 80°C, 1 h, 80%; (iiia) N-methylhomopiperazine (5 equiv), no solvent, microwave heating, 80°C, 4 h,65%; (iiib) N-methylhomopiperazine (5 equiv), no solvent, microwave heating, 120°C, 3 h, 55%; (iiic) N-methylpiperazine (10 equiv), N-methylpiperazine hydrochloride (10 equiv), DMSO, 110–120°C, 20 h, 56%.