Synthesis of pyrido[2,3-d]pyrimidines. Reagents and conditions: (i) X-NH2, Et3N, THF; rt, 1–3 h, 80–95%; (ii) LiAlH4, THF, −10 °C–rt, 1 h, 80–86%; (iii) MnO2, CHCl3, rt, 24 h, 70–90%; (iv) active methylene compounds, BnNH2, AcOH, 100 °C, 6 h, 32–67%; (v) m-CPBA, CH2Cl2, rt, 3 h, 54–86%; (vi) Z, DMSO or toluene, 100 °C, 3–8 h, 45–65%.