Scheme 1.

Synthesis of piperazine-linked aminopyridine derivatives. Reagents and conditions: (a) K₂S₂O₈, H₂SO₄, 90 °C, 24 h, 45%; (b) 1-Boc-piperazine, K₂CO₃, toluene, 50 °C, 15 h, 42%; (c) trifluoroacetic acid (TFA), dichloromethane (DCM), rt, 4 h, 79%; (d) R₁X, K₂CO₃, dimethylformamide (DMF), rt, 5 h, 40–93%; (e) resorcinol, Cs₂CO₃, DMF, 70 °C, 24 h, 20–79%; (f) acryloyl chloride, triethylamine (TEA), DCM, 0 °C, 3 h, 6–67%; (g) SnCl₂∙2H₂O, EtOH, 0 °C, 1 h, 4–23%.