Scheme 4 Reagents and conditions: (i) (pyridin-2-ylmethyl)amine, (3-bromopropyl)amine, or N-(pyridin-2-yl)propane-1,3-diamine, Et₂O/EtOH (3:1)rt; (ii) K₂CO₃, dry DMF rt, 80°C; (iii) 1-(2-pyridinyl)piperazine, dry DMF, K₂CO₃, 80°C; (iv) piperazine, DIPEA, dry DMF, 80°C; (v) H₂, Raney Ni, DMF; (vi) 4% NaOH, reflux.