Scheme 1. Synthesis of phthalazine derivatives 6a–6g. Reagents and conditions: (a) K₂CO₃, DMF, 90 °C, overnight, yield: 48%; (b) bis(pinacolate)diboron, KOAc, PdCl₂(dppf), dioxane, reflux, overnight; (c) Na₂CO₃, ethanol/water/toluene, Pd(PPh₃)₄, 80 °C, 8 h, yield: 13–40%.